RNA-binding Protein With Multiple Splicing Research Articles

Crystallin β-b2 promotes retinal ganglion cell protection in experimental autoimmune uveoretinitis.

Crystallin βb2 (crybb2) is upregulated in regenerating retinas and in various pathological conditions of the retina, including uveoretinitis. However, the role of crybb2 in this disease is largely unknown. Therefore, we used recombinant crybb2 (rcrybb2) as intravitreal treatment of B10.RIII mice prior to immunization with human interphotoreceptor retinoid-binding protein peptide 161-180 (hIRBPp161-180) in complete Freund's adjuvant (CFA) and concomitant injection of pertussis toxin (PTX) to induce experimental autoimmune uveoretinitis (EAU). In naïve mice, more beta III-tubulin (TUBB3) + and RNA-binding protein with multiple splicing (RBPMS) + cells were found in the ganglion cell layer of the retina than in EAU eyes, suggesting a loss of retinal ganglion cells (RGC) during the development of EAU. At the same time, the number of glial fibrillary acidic protein (GFAP) + cells increased in EAU eyes. RGCs were better protected in EAU eyes treated with rcrybb2, while the number of GFAP+ cells decreased. However, in retinal flatmounts, both retinal ganglion cells and retinal endothelial cells stained positive for TUBB3, indicating that TUBB3 is present in naïve B10.RIII mouse eyes not exclusive to RGCs. A significant decline in the number of RBPMS-positive retinal ganglion cells was observed in retinal flatmounts from EAU retinas in comparison to naïve retinas or EAU retinas with intravitreal rcrybb2 treatment. Whereas no significant decrease in TUBB3 levels was detected using Western blot and RT-qPCR, GFAP level, as a marker for astrocytes, increased in EAU mice compared to naïve mice. Level of Bax and Bcl2 in the retina was altered by treatment, suggesting better cell survival and inhibition of apoptosis. Furthermore, our histologic observations of the eyes showed no change in the incidence and severity of EAU, nor was the immune response affected by intravitreal rcrybb2 treatment. Taken together, these results suggest that intravitreal injection of rcrybb2 reduces retinal RGC death during the course of EAU, independent of local or systemic autoimmune responses. In the future, treating posterior uveitis with rcrybb2 to protect RGCs may offer a promising novel therapeutic strategy.

Induced Attenuation of Scleral TGF-β Signaling in Mutant Mice Increases Susceptibility to IOP-Induced Optic Nerve Damage.

Axonal optic nerve (ON) damage in glaucoma is characteristically associated with increased amounts of active transforming growth factor-beta 2 (TGF-β2) in the ON head. Here we investigated the functional role of scleral TGF-β signaling in glaucoma. A deficiency of Tgfbr2, which encodes for TGF-β receptor type II (TGF-βRII), the essential receptor for canonical TGF-β signaling, was induced in fibroblasts (including those of the sclera) of mutant mice. To this end, 5-week-old mice were treated with tamoxifen eye drops. Experimental glaucoma was induced in 8-week-old mice using a magnetic microbead (MB) model. After 6 weeks of high intraocular pressure (IOP), the ON axons and their somata in the retina were labeled by paraphenylenediamine (PPD) and RNA-binding protein with multiple splicing (RBPMS) immunohistochemistry, respectively, and quantified. Tamoxifen treatment resulted in a significant decrease of TGF-βRII and its mRNA in the sclera. After 6 weeks of high IOP, reduced numbers of PPD-stained ON axons were seen in MB-injected eyes in comparison with not-injected contralateral eyes. Moreover, MB injection also led to a decrease of retinal ganglion cell (RGC) somata as seen in RBPMS-stained retinal wholemounts. Axon loss and RGC loss were significantly higher in mice with a fibroblast specific deficiency of TGF-βRII in comparison with control animals. We conclude that the ablation of scleral TGF-β signaling increases the susceptibility to IOP-induced ON damage. Scleral TGF-β signaling in mutant mice appears to be beneficial for ON axon survival in experimentally induced glaucoma.

Abstract 13603: Inhibition of Exercise-Regulated Long Noncoding RNA SALTe1 Reverses Vascular Aging and Age-Related Cardiac Dysfunction

Rationale: Age is a major risk factor for cardiovascular disease. Recent work suggests vascular aging is an important determinant of longevity and end-organ function, although its role in age-related cardiac dysfunction and how exercise mitigates these phenotypes remain unclear. Objective: To identify exercise-regulated, cardiac long noncoding RNAs (lncRNAs) that modulate vascular aging. Methods and Results: Twenty-month-old mice underwent voluntary wheel running for eight weeks. RNAseq identified a novel set of lncRNAs altered in exercised aged hearts, termed S enescence A ssociated L ncRNA T ranscripts in E xercise (SALTes). SALTe1 was conserved and primarily expressed in endothelial cells (ECs). SALTe1 increased in aged hearts but decreased with exercise. Myocardial perfusion and CD31 positive cells were reduced in 20-month-old vs 10-week-old mice while EC senescence (CD31 and p16 or γH2AX double-positive cells) and cardiac diastolic dysfunction increased (p<0.05 for all). In 20-month-old mice, SALTe1 inhibition using antisense GapmeR or EC-specific knockdown in CAS9-mice reversed multiple hallmarks of vascular aging. Recovery from hindlimb ischemia improved (post-surgery day 28 perfusion ratio, Control: 0.58±0.03 vs GapmeR: 0.73±0.03, p=0.04, n=12/group) and aortic stiffness was reduced to levels seen in young animals. Myocardial perfusion (time-to-peak, Control: 2.585±0.08 vs GapmeR: 2.048±0.11 seconds, p=0.03, n=12/group) improved. Cardiac EC number increased, and EC senescence decreased (p<0.05 for all). Inhibition of SALTe1 reduced E/E’ (-20.16±1.60 vs -15.4±1.10, p=0.04, n=12/group) and increased global longitudinal strain (-15.88±0.84 vs 20.66±1.02, p=0.02, n=12/group). Mechanistic studies in vitro and in vivo revealed that SALTe1 works through regulation of Poly (ADP-Ribose) Polymerase Family Member 9 (PARP9) and RNA-binding protein with multiple splicing (RBPMS). Conclusions: SALTe1 regulates EC senescence through PARP9 and RBPMS. SALTe1 inhibition reverses multiple hallmarks of vascular aging and improves age-related cardiac dysfunction. These findings suggest a primary role for EC senescence in age-related cardiac dysfunction and identify SALTe1 as a potential new therapeutic target.

Pan-cancer tRNA-derived fragment CAT1 coordinates RBPMS to stabilize NOTCH2 mRNA to promote tumorigenesis

Transfer RNA-derived fragments (tRFs) are a class of small non-coding regulatory RNAs that are involved in the pathophysiology of many diseases. However, the role of tRFs in cancer progression remains largely elusive. Here, we demonstrate that a pan-cancer 3'-tRF, CAT1 (cancer associated tRF 1), is ubiquitously upregulated in tumors and associated with poor prognosis of a variety of cancers, including lung cancer. The upregulated CAT1 in cancer cells binds to RNA-binding protein with multiple splicing (RBPMS) and displaces NOTCH2 association from RBPMS, thereby inhibiting the subsequent CCR4-NOT deadenylation-complex-mediated NOTCH2 mRNA decay. The CAT1-enhanced NOTCH2 expression promotes lung cancer cell proliferation and metastasis invitro and invivo. In addition, plasma CAT1 levels are substantially increased in patients with lung cancer compared to non-cancer control subjects. Our findings reveal an intrinsic connection between cancer-specific upregulation of CAT1 and cancer progression, show the regulation of NOTCH signaling in cancer by a 3'-tRF, and highlight its great clinical potential.

RBPMS regulates cardiomyocyte contraction and cardiac function through RNA alternative splicing.

RNA binding proteins play essential roles in mediating RNA splicing and are key post-transcriptional regulators in the heart. Our recent study demonstrated that RBPMS (RNA binding protein with multiple splicing) is crucial for cardiac development through modulating mRNA splicing, but little is known about its functions in the adult heart. In this study, we aim to characterize the post-natal cardiac function of Rbpms and its mechanism of action. We generated a cardiac-specific knockout mouse line and found that cardiac-specific loss of Rbpms caused severe cardiomyocyte contractile defects, leading to dilated cardiomyopathy and early lethality in adult mice. We showed by proximity-dependent biotin identification assay and mass spectrometry that RBPMS associates with spliceosome factors and other RNA binding proteins, such as RBM20, that are important in cardiac function. We performed paired-end RNA sequencing and RT-PCR and found that RBPMS regulates mRNA alternative splicing of genes associated with sarcomere structure and function, such as Ttn, Pdlim5, and Nexn, generating new protein isoforms. Using a minigene splicing reporter assay, we determined that RBPMS regulates target gene splicing through recognizing tandem intronic CAC motifs. We also showed that RBPMS knockdown in human induced pluripotent stem cell-derived cardiomyocytes impaired cardiomyocyte contraction. This study identifies RBPMS as an important regulator of cardiomyocyte contraction and cardiac function by modulating sarcomeric gene alternative splicing.

The RBPMSCreERT2-tdTomato mouse line for studying retinal and vascular relevant diseases

RNA-binding protein with multiple splicing (RBPMS) plays a crucial role in cardiac mesoderm specification and cardiovascular development, as well as being a typical marker for whole retinal ganglion cells (RGCs). However, there is a lack of animal models to spatiotemporally trace the location and function of RBPMS-expressing cells invivo. In this study, we develop a tamoxifen-inducible RBPMS-tdTomato reporter mouse line to track RBPMS-expressing cells during embryogenesis and adulthood. This mouse line allows us to identify and locate RBPMS-tdTomato-positive cells among various tissues, especially in RGCs and smooth muscle cells, which assist to simulate related retinal degenerative diseases, model and examine choroidal neovascularization non-invasively invivo. Our results show that the RBPMSCreERT2-tdTomato mouse line is a valuable tool for lineage tracing, disease modeling, drug screening, as well as isolating specific target cells.

Abstract P3041: Stage-specific Alternative Rna Splicing Attunes Cardiomyocyte Proliferation And Contraction

During heart development, cardiomyocytes display reduced proliferation and enhanced contractility to support cardiac functional maturation, but the mechanistic basis is not fully understood. Alternative RNA splicing is an important mechanism of RNA posttranscriptional modification and gene regulation in the heart. In studying a cardiac RNA binding protein, RBPMS (RNA-binding protein with multiple splicing), we found that RBPMS mediates distinct RNA splicing profiles in adult hearts versus neonatal hearts, indicating its stage-specific modulation of alternative RNA splicing. We showed that RBPMS regulates the splicing of cytoskeletal genes to enable proliferation of neonatal cardiomyocytes. In adult hearts, RBPMS regulates the splicing of sarcomere genes to support cardiac contraction. Cardiac-specific loss of RBPMS causes severe dilated cardiomyopathy and early lethality in adult mice. Using both in vivo and in vitro approaches, we found that the absence of RBPMS caused aberrant splicing of some key sarcomeric components, including Titin and Nexilin, causing cardiomyocyte contractile defects. Intriguingly, we also showed that RBPMS interacts with other cardiac RNA binding proteins, such as RBM20, suggesting their synergistic effects on cardiomyocyte physiology. Our work provides novel insights into how RNA binding proteins regulate cardiomyocyte proliferation and contraction by mediating alternative RNA splicing.

Inducible Rbpms-CreERT2 Mouse Line for Studying Gene Function in Retinal Ganglion Cell Physiology and Disease.

Retinal ganglion cells (RGCs) are the sole output neurons conveying visual stimuli from the retina to the brain, and dysfunction or loss of RGCs is the primary determinant of visual loss in traumatic and degenerative ocular conditions. Currently, there is a lack of RGC-specific Cre mouse lines that serve as invaluable tools for manipulating genes in RGCs and studying the genetic basis of RGC diseases. The RNA-binding protein with multiple splicing (RBPMS) is identified as the specific marker of all RGCs. Here, we report the generation and characterization of a knock-in mouse line in which a P2A-CreERT2 coding sequence is fused in-frame to the C-terminus of endogenous RBPMS, allowing for the co-expression of RBPMS and CreERT2. The inducible Rbpms-CreERT2 mice exhibited a high recombination efficiency in activating the expression of the tdTomato reporter gene in nearly all adult RGCs as well as in differentiated RGCs starting at E13.5. Additionally, both heterozygous and homozygous Rbpms-CreERT2 knock-in mice showed no detectable defect in the retinal structure, visual function, and transcriptome. Together, these results demonstrated that the Rbpms-CreERT2 knock-in mouse can serve as a powerful and highly desired genetic tool for lineage tracing, genetic manipulation, retinal physiology study, and ocular disease modeling in RGCs.

Increased Expression of the RBPMS Splice Variants Inhibits Cell Proliferation in Ovarian Cancer Cells.

RNA-Binding Protein with Multiple Splicing (RBPMS) is a member of family proteins that bind to nascent RNA transcripts and regulate their splicing, localization, and stability. Evidence indicates that RBPMS controls the activity of transcription factors associated with cell growth and proliferation, including AP-1 and Smads. Three major RBPMS protein splice variants (RBPMSA, RBPMSB, and RBPMSC) have been described in the literature. We previously reported that reduced RBPMS levels decreased the sensitivity of ovarian cancer cells to cisplatin treatment. However, little is known about the biological role of the RBPMS splice variants in ovarian cancer cells. We performed RT-PCR and Western blots and observed that both RBPMSA and RBPMSC are reduced at the mRNA and protein levels in cisplatin resistant as compared with cisplatin sensitive ovarian cancer cells. The mRNA and protein levels of RBPMSB were not detectable in any of the ovarian cancer cells tested. To better understand the biological role of each RBPMSA and RBPMSC, we transfected these two splice variants in the A2780CP20 and OVCAR3CIS cisplatin resistant ovarian cancer cells and performed cell proliferation, cell migration, and invasion assays. Compared with control clones, a significant reduction in the number of colonies, colony size, cell migration, and invasion was observed with RBPMSA and RBPMSC overexpressed cells. Moreover, A2780CP20-RBPMSA and A2780CP20-RBPMSC clones showed reduced senescence-associated β-galactosidase (β-Gal)-levels when compared with control clones. A2780CP20-RBPMSA clones were more sensitive to cisplatin treatment as compared with A2780CP20-RBPMSC clones. The A2780CP20-RBPMSA and A2780CP20-RBPMSC clones subcutaneously injected into athymic nude mice formed smaller tumors as compared with A2780CP20-EV control group. Additionally, immunohistochemical analysis showed lower proliferation (Ki67) and angiogenesis (CD31) staining in tissue sections of A2780CP20-RBPMSA and A2780CP20-RBPMSC tumors compared with controls. RNAseq studies revealed many common RNA transcripts altered in A2780CP20-RBPMSA and A2780CP20-RBPMSC clones. Unique RNA transcripts deregulated by each RBPMS variant were also observed. Kaplan-Meier (KM) plotter database information identified clinically relevant RBPMSA and RBPMSC downstream effectors. These studies suggest that increased levels of RBPMSA and RBPMSC reduce cell proliferation in ovarian cancer cells. However, only RBPMSA expression levels were associated with the sensitivity of ovarian cancer cells to cisplatin treatment.

Isozyme-specific histone deacetylase 1/2 inhibitor K560 attenuates oxidative stress-induced retinal cell death

Oxidative stress-induced damage is an underlying mechanism in the pathogenesis of age-related retinal diseases. Here, we examined the effects of K560, a potential candidate drug for the treatment of these diseases, on oxidative stress-induced retinal cell death. K560 is a novel isozyme-specific inhibitor of histone deacetylase 1 and 2 (HDAC1/2). Histone acetylation in retinal lysates and dissociated retinal cells was detected with a western blot analysis and cell-based enzyme-linked immunosorbent assay (ELISA), respectively. The viability of mouse retinal cells was measured with an alamarBlue assay. We used immunohistochemistry for RNA binding protein with multiple splicing (RBPMS) to visualize the retinal ganglion cells (RGCs) of mice. An ELISA analysis indicated that histone acetylation was enhanced in dissociated mouse retinal cells treated with K560. The cell viability assay indicated that K560 attenuated both exogenous hydrogen peroxide–induced and endogenous oxidative stress–induced cell death in dissociated retinal cells. Western blot analysis indicated that intravitreal K560 administration enhanced the acetylation of histones H3 and H4 in mouse retinal lysates. To examine the effect of K560 on oxidative stress–induced RGC death, we performed whole-mount immunohistochemistry for RBPMS on retinas dissected from eyes treated with K560 or vehicle on day one, and K560 or vehicle and NMDA on day two. Quantification of RBPMS-immunopositive cells indicated that K560 attenuated NMDA-induced RGC death. Taken together, our findings suggest that administration of a HDAC1/2-specific inhibitor K560 may be effective in the treatment of oxidative stress–mediated retinal degeneration and have less cytotoxicity than other known HDAC inhibitors, which are known to target a wide range of HDAC family members.

Changes in glial cells and neurotrophic factors due to rotenone-induced oxidative stress in Nrf2 knockout mice

Glaucoma is one of the most common causes of blindness worldwide. It is thought to be a multifactorial disease with underlying mechanisms that include mitochondrial dysfunction and oxidative stress. Here, we used NF-E2 related factor 2 (Nrf2) knockout (KO) mice, which are vulnerable to oxidative stress, to examine a neuroprotective effect against oxidative stress due to rotenone, a mitochondrial complex I inhibitor. Wild-type (WT) and Nrf2 KO mice received an oral solution of rotenone for 30 days. We then extracted the retinas and performed immunohistochemistry and quantitative RT-PCR. We also prepared a primary Müller cell culture of samples from each mouse, added 30 μM rotenone, and then measured cell viability, cytotoxicity and CellRox absorbance. We also examined gene expression. We found a significant increase in the number of 8-OHdG-positive retinal ganglion cells (RGCs) after rotenone administration in both the WT and Nrf2 KO mice. There was no difference in the number of RNA-binding protein with multiple splicing (RBPMS)-positive RGCs in the WT and Nrf2 KO mice, but Nrf2 KO mice that were given rotenone had significantly less retinal gene expression of RBPMS than Nrf2 KO mice given a control. Moreover, there was significantly higher mRNA gene expression of vimentin and glial fibrillary acidic protein (GFAP) in Nrf2 KO mice that received rotenone than WT mice that received rotenone. A statistical analysis of the in vitro experiment showed that cell viability was lower, cytotoxicity was higher, and oxidative stress was higher in the Müller cells of the Nrf2 KO mice than the WT mice. Finally, brain-derived neurotrophic factor (BDNF) and basic fibroblast growth factor (bFGF) were significantly higher in the Müller cells of the Nrf2 KO mice than the WT mice. These findings suggest that in Nrf2 KO mice under oxidative stress caused by rotenone, temporary neurotrophic factors are secreted from the Müller cells, conferring neuroprotection in these cells.

Ambient particulate matter exposure causes visual dysfunction and retinal neuronal degeneration

PM2.5 pollution is related to neurotoxic and vascular effects in eye diseases such as glaucoma. This study investigates the adverse effects of PM2.5 exposure on visual function and retinal neurons. A versatile aerosol concentration enrichment system was used to expose mice to either control air or PM2.5 polluted air. Six months after PM2.5 exposure, visual function was measured by electroretinography (ERG). Hematoxylin and eosin staining and immunofluorescence staining were used for histopathological analysis. Protein markers of apoptosis, astrocytic reactivity, inflammatory cytokines, lipid peroxidation, protein nitration and DNA damage response were quantified with ELISA, western blot or detected using immunofluorescence and immunohistochemistry. After six months of exposure, PM2.5-exposed mice responded poorly to light stimuli compared with those exposed to the control air. PM2.5 exposure caused retinal thinning and reduction in the expression of retinal ganglion cell-selective marker RNA-binding protein with multiple splicing (RBPMS). Further, positive TUNEL staining was observed in the inner nucleus and outer nuclear layers of the retinae after exposure to PM2.5, which was accompanied by the activation of apoptosis signaling molecules p53, caspase-3 and Bax. PM2.5 induced the release of inflammatory cytokines including tumor necrosis factor-α and cleaved interleukin-1β. Furthermore, increased levels of 8-OHdG and γ-H2AX in the mouse retinea were indicative of DNA single and double strand breaks by PM2.5 exposure, which activated PARP-1 mediated DNA damage and repair. In conclusion, this study demonstrates sub-chronic systemic exposure to concentrated PM2.5 causes visual dysfunction and retinal neuronal degeneration. Data availabilityThe datasets during and/or analyzed during the current study available from the corresponding author on reasonable request.

219 (PB099) - The RNA-Binding Protein with Multiple Splicing (RBPMS) splice variants A and C, acts as a tumor suppressor gene in ovarian cancer

RNA-Binding Protein with Multiple Splicing (RBPMS) is a member of a family of proteins that bind to nascent RNA transcripts and regulate their processing, and stability of the RNA molecules. Evidence indicates that RBPMS also control de activity of transcription factors associated with cell proliferation including AP-1 and STATs. Three major RBPMS protein splice variants have been described in the literature: RBPMSA, RBPMSB, and RBPMSC. We previously reported that reduced RBPMS levels decreased the sensitivity of ovarian cancer (OC) cells to cisplatin treatment.

Role of RNA Binding Protein with Multiple Splicing (RBPMS) Variants in Cell Proliferation, Invasion and Angiogenesis in Ovarian Cancer

Worldwide, the number of cancer‐related deaths continues to increase due to the ability of cancer cells to become chemotherapy‐resistant and metastasize. For women with ovarian cancer, a staggering 70% will become resistant to the front‐line therapy, cisplatin. RNA binding protein with multiple splicing (RBPMS) is a member of family proteins that bind to the nascent RNA transcripts regulate their processing, which includes splicing, transport, localization and stability. Evidence indicates that RBPMS interact with c‐Fos, a member of the AP‐1 family that dimerizes with c‐Jun to stimulate AP‐1 transcriptional activity. Furthermore, RBPMS interacted with transcription factor Smad3, which bind to c‐Jun increasing AP‐1 transcriptional activity. Three major RBPMS isoforms have been described, RBPMS‐A (21.8 kDa), RBPMS‐B (22.4 kDa) and RBPMS‐C (24.2 kDa). Reports have shown that each RBPMS isoform interacts with proteins and/or RNAs responsible for cell growth, proliferation, and tumor progression. Previous reports of our laboratory have found that RBPMS expression decrease in cisplatin resistance compared with cisplatin sensitive cells. However, the specific RBPMS isoform responsible of this observation has not been elucidated and less is known about its role on invasiveness ability and angiogenesis capacity. We overexpressed each RBPMS variants (A, B and C) in the cisplatin resistant ovarian cancer cells, A2780CP20, and performed cell viability, cell proliferation and invasion assays. Significant reduction in the number of colonies and their area were observed in both isoform A and isoform C clones, compared with isoform B and control empty vector clones. However, clones of isoform A were more sensitive to cisplatin treatment in comparation with isoform B and C clones. In vivo experiments showed a significant reduction in tumor growth between RBPMS A and C when compared with the controls. Tumor tissues were subjected to immunohistochemical analysis for proliferation (Ki67) and angiogenesis (CD31). Elevated signals of both antibodies were detected in tissues from control groups when compared with RBPMS A and C overexpressing tumor tissues. These studies along with the RNAseq suggest that RBPMS, regulate transcripts involved in cell proliferation and invasion capacity of ovarian cancer cells. Moreover, RBPMS A and C represses uncontrolled proliferation, invasiveness, and angiogenesis in ovarian cancer cells. However, only the isoform A contributed to the cisplatin sensitivity of ovarian cancer cells. Future efforts on this project will be focused on determining the RBPMS isoform that represses AP‐1 (c‐Fos and c‐Jun) dependent gene regulation in cisplatin sensitive ovarian cancer cells.

Reduced RBPMS Levels Promote Cell Proliferation and Decrease Cisplatin Sensitivity in Ovarian Cancer Cells.

Worldwide, the number of cancer-related deaths continues to increase due to the ability of cancer cells to become chemotherapy-resistant and metastasize. For women with ovarian cancer, a staggering 70% will become resistant to the front-line therapy, cisplatin. Although many mechanisms of cisplatin resistance have been proposed, the key mechanisms of such resistance remain elusive. The RNA binding protein with multiple splicing (RBPMS) binds to nascent RNA transcripts and regulates splicing, transport, localization, and stability. Evidence indicates that RBPMS also binds to protein members of the AP-1 transcription factor complex repressing its activity. Until now, little has been known about the biological function of RBPMS in ovarian cancer. Accordingly, we interrogated available Internet databases and found that ovarian cancer patients with high RBPMS levels live longer compared to patients with low RBPMS levels. Similarly, immunohistochemical (IHC) analysis in a tissue array of ovarian cancer patient samples showed that serous ovarian cancer tissues showed weaker RBPMS staining when compared with normal ovarian tissues. We generated clustered regularly interspaced short palindromic repeats (CRISPR)-mediated RBPMS knockout vectors that were stably transfected in the high-grade serous ovarian cancer cell line, OVCAR3. The knockout of RBPMS in these cells was confirmed via bioinformatics analysis, real-time PCR, and Western blot analysis. We found that the RBPMS knockout clones grew faster and had increased invasiveness than the control CRISPR clones. RBPMS knockout also reduced the sensitivity of the OVCAR3 cells to cisplatin treatment. Moreover, β-galactosidase (β-Gal) measurements showed that RBPMS knockdown induced senescence in ovarian cancer cells. We performed RNAseq in the RBPMS knockout clones and identified several downstream-RBPMS transcripts, including non-coding RNAs (ncRNAs) and protein-coding genes associated with alteration of the tumor microenvironment as well as those with oncogenic or tumor suppressor capabilities. Moreover, proteomic studies confirmed that RBPMS regulates the expression of proteins involved in cell detoxification, RNA processing, and cytoskeleton network and cell integrity. Interrogation of the Kaplan–Meier (KM) plotter database identified multiple downstream-RBPMS effectors that could be used as prognostic and response-to-therapy biomarkers in ovarian cancer. These studies suggest that RBPMS acts as a tumor suppressor gene and that lower levels of RBPMS promote the cisplatin resistance of ovarian cancer cells.

Modulation of Sirt1-mTORC1 Pathway in Microglia Attenuates Retinal Ganglion Cell Loss After Optic Nerve Injury.

PurposeOptic nerve injury (ONI) causes neuroinflammation and neurodegeneration leading to visual deficits. The response of microglia has emerged as an impactful component of etiology in neurodegeneration. This study aimed to investigate the effect of SIRT1-mTORC1 signaling pathway in microglia regulation after ONI.MethodsCx3Cr1-CreERT2/RaptorF/F and Cx3Cr1-CreERT2/Sirt1F/F mice were used to delete Raptor and Sirt1 in microglia, respectively. Optic nerve crush (ONC) model was established to mimic ONI. PLX5622, a highly specific inhibitor of the colony-stimulating factor 1 receptor (CSF1R), is used to eliminate microglia in optic nerve. Ionized calcium binding adaptor molecule 1 (Iba1) immunostaining was used to detect microglial activation. Retinal ganglion cells (RGCs) were quantified by Nissl staining and retinal whole-mount immunostaining with RNA-binding protein with multiple splicing (RBPMS). Axonal damage was valued by transmission electron microscopy (TEM).ResultsMicroglial activation emerged on day 3 post ONC and was earlier than RGCs loss which occurred at day 5 after injury. Depleting microglia with PLX5622 could attenuate the loss of RGCs and axon damage after ONC. Gain- and loss-of-function studies revealed that SIRT1 determined the activation of microglia in optic nerve. In addition, microglia-specific deletion of Raptor resulted in decreased microglial activation. Interestingly, activating mTORC1 with CCT007093 could reverse the function of SIRT1 in regulating the process of microglial activation mediated RGCs loss.ConclusionOur study reveals a potential novel mechanism of SIRT1-mTORC1 pathway in microglia regulation, and indicates a therapeutic potential for the protection of RGCs in ONI.

Investigating the role of Ca2+/calmodulin-dependent protein kinase II in the survival of retinal ganglion cells.

Investigating the role of Ca2+/calmodulin-dependent protein kinase II in the survival of retinal ganglion cells.

Differential Retinal Protein Expression in Primary and Secondary Retinal Ganglion Cell Degeneration Identified by Integrated SWATH and Target-Based Proteomics.

To investigate the retinal proteins associated with primary and secondary retinal ganglion cell (RGC) degeneration and explore their molecular pathways, SWATH label-free and target-based mass spectrometry was employed to identify the proteomes in various retinal locations in response to localized optic nerve injury. Unilateral partial optic nerve transection (pONT) was performed on adult Wistar rats and their retinas were harvested 2 weeks later. To confirm the separation of primary and secondary RGC degeneration, immunohistochemistry of RNA binding protein with multiple splicing (RBPMS) and glial fibrillary acidic protein (GFAP) was performed on retinal whole-mounts. Retinal proteomes in the temporal and nasal quadrants were evaluated with high resolution hybrid quadrupole time-of-flight mass spectrometry (QTOF-MS), and SWATH-based acquisition, and their expression was compared to the corresponding retinal quadrant in contralateral control eyes and further validated by multiple reaction monitoring mass spectrometry (MRM-MS). A total of 3641 proteins (FDR < 1%) were identified using QTOF-MS. The raw data are available via ProteomeXchange with the identifier PXD026783. Bioinformatics data analysis showed that there were 37 upregulated and 25 downregulated proteins in the temporal quadrant, whereas 20 and five proteins were upregulated and downregulated, respectively, in the nasal quadrant, respectively (n = 4, p < 0.05; fold change ≥ 1.4-fold or ≤0.7). Six proteins were regulated in both the temporal and the nasal quadrants, including CLU, GFAP, GNG5, IRF2BPL, L1CAM, and CPLX1. Linear regression analysis indicated a strong association between the data obtained by means of SWATH-MS and MRM-MS (temporal, R2 = 0.97; nasal, R2 = 0.96). Gene ontology analysis revealed statistically significant changes in the biological processes and cellular components of primary RGC degeneration. The majority of the significant changes in structural, signaling, and cell death proteins were associated with the loss of RGCs in the area of primary RGC degeneration. The combined use of SWATH-MS and MRM-MS methods detects and quantifies regional changes of retinal protein expressions after localized injury. Future investigation with this integrated approach will significantly increase the understanding of diverse processes of progressive RGC degeneration from a proteomic prospective.

Inhibition of the Epigenetic Modifier EZH2 By Mir-138 Upregulates Tumor Suppressor Gene Rbpms and Contributes to Drug Susceptibility in Preclinical Model of Multiple Myeloma

Multiple myeloma (MM) is a plasma cell malignancy driven by numerous genetic and epigenetic alterations including miRNA aberration. Several studies have shown that enhancer of zeste homologue 2 (EZH2) is overexpressed in MM. However, the detailed oncogenic mechanism of EZH2 in drug resistance of MM is not clear. Our previous study showed that miR-138 is an EZH2 target gene, which was epigenetically silenced by histone methylation in its promoter region in drug resistant MM cell lines and primary patient samples. Moreover, luciferase reporter assay confirmed direct targeting of EZH2 by miR-138 in MM cells, suggesting a double negative feedback loop between miR-138 and EZH2 in MM. We also identified that EZH2 and miR-138 expression were negatively correlated in primary patient samples. Here, we investigated how unbalanced miR-138/EZH2 regulatory axis is involved in pathogenesis and drug resistance of MM.To examine the functional effect of miR-138 on cell proliferation and apoptosis in MM cells, two resistant cell lines (8226-R5 and MM.1R) were transduced with miR-138 precursor or scramble lentiviruses and treated with different anti-myeloma drugs including bortezomib (BTZ) , lenalidomide (Len), dexamethasone (Dex) and doxorubicin (Dox). Overexpression of miR-138 in drug resistant cells could re-sensitize the resistant cells to anti-myeloma drugs. Also, reduction of cell proliferation upon overexpression of miR-138 was associated with apoptosis of the resistant cells. In addition, we explored whether EZH2 could rescue the effect of miR-138 on MM cells growth. To this end, we performed functional rescue assay by overexpressing EZH2 in 8226-R5 and MM.1R cells and co-transfecting with miR-138 mimics or scramble. EZH2 overexpression partially abolished the anti-tumor effect induced by miR-138 and BTZ confirming that combination of miR-138 and BTZ induces an inhibitory effect in MM cells by targeting EZH2.Furthermore, to investigate the downstream mechanism of EZH2 targeting in MM drug resistance, H3K27me3 ChIP-seq and genome-wide profiling datasets were analyzed and revealed that the EZH2 target gene, RNA-binding protein with multiple splicing (RBPMS), was significantly silenced in MM in comparison to other types of cancers. It was also downregulated in ISS stage III of MM compared to stage I and II. Notably, we identified that RBPMS was downregulated in 8226-R5 and MM1.R resistant cell lines in comparison to 8226 and MM1.S cells, respectively. The ChIP-qPCR also showed that the histone H3K27 was significantly methylated in the promoter region of RBPMS in drug resistant cells and primary patient samples in comparison to parental lines and normal donor samples, respectively. Additionally, functional study on RBPMS silenced cells revealed that knockdown of RBPMS could confer drug resistance to parental MM cells, suggesting a tumor suppressor activity for RBPMS in MM. Remarkably, targeting of EZH2 by miR-138 overexpression could restore the RBPMS expression level in drug resistant cells.In order to translate our findings to a therapeutic model, we next stablished a mouse xenograft model and investigated the effect of miR-138 on tumorigenesis of MM resistant cells in vivo. Intratumoral injection of synthetic miR-138 significantly suppressed tumorigenesis in combination with BTZ. The miR-138 or BTZ alone moderately prolonged survival compared to control treatment. However, the combination treatment of miR-138 mimics and BTZ significantly extended the overall survival (p= 0.0395). In addition, EZH2 protein and mRNA level were decreased in miR-138 mimics treated groups compared with controls whereas the expression of RBPMS was induced, indicating in vivo targeting of EZH2 by miR-138. IHC analysis of xenograft tumor sections showed that combination treatment of miR-138 mimics and BTZ resulted in a decrease in the proliferation index (Ki67) and an increase in the apoptotic index (Tunnel), compared to either BTZ or miR-138 mimics alone. Collectively, these results support that miR-138 functions as a tumor suppressor miRNA and contributes to the effect of EZH2 on MM cell growth and drug resistance.Our findings indicate that targeting of EZH2 by miR-138 sensitizes MM cells to anti-myeloma drugs and contributes to induction of apoptosis of MM cells, as well as suppression of MM tumor growth in vivo and could be a potential candidate for clinical application to the treatment of MM. DisclosuresNo relevant conflicts of interest to declare.

Abstract PO049: Compartment-specific profiling for evaluation of disrupted signaling in early stage, low-grade endometrial cancer

Abstract Understanding tumor microenvironment is critical to improving conservative management (non-surgical) strategies for early stage, low grade endometrial cancer (EC). This remains an unmet clinical need for women who wish to maintain fertility and those who cannot undergo surgery due to medical co-morbidities. Current regimens rely on progestin treatment, but resistance and early relapse require improved therapeutic strategies. We sought to evaluate alterations in gene expression in the epithelial and stromal compartment of EC compared to normal endometrium to identify targets for combination therapies. RNA was extracted from microdissected epithelial and stromal compartments of formalin fixed paraffin embedded early stage, low grade EC and normal endometrium (NE). Comprehensive transcriptome profiling was performed with Affymetrix Clariom D assay and pathway analysis was performed. Immunohistochemistry (IHC) was used for validation. Functional studies of differentially expressed genes were performed in Hec1A EC cell lines. Among differentially expressed genes in EC vs NE, multiple altered signaling pathways were identified. EIF2 signaling, eIF4 and p70S6K signaling, and PI3K/AKT/mTOR were the most significant pathways activated in both epithelial and stromal compartments. In the epithelia compartment, the most significant gene expression changes included reduced expression of RBPMS (RNA Binding Protein with Multiple Splicing), SORD (Sorbitol Dehydrogenase), DDX17 (DEAD-Box Helicase 17), and TPT1 (Translationally-Controlled Tumor Protein) in EC, while MTDH (Metadherin) was significantly increased in EC. Similar changes were observed in the stroma compartment, but with lower fold changes than that observed in gland. Together with decreased RBPMS expression, decreased RBPMS-interacting molecules IGF2, TCF7L2 (Transcription Factor 7 Like 2), FOS (Proto-Oncogene C-Fos) and increased GPS2 (G protein Pathway Suppressor 2) were also observed. Differential expression of proteins in gland and stroma was also confirmed by IHC. An inverse correlation of RBPMS expression and EC proliferation was also observed in EC at the protein level. Enhanced AKT and S6 protein phosphorylation were observed by RBPMS silencing in Hec1A endometrial cells. Reverse Phase Protein Array demonstrated activation of Caveolin 1, FOXO3 (Forkhead Box O3), MT-CO1 (Mitochondrially Encoded Cytochrome C Oxidase I), L1CAM (L1 Cell Adhesion Molecule) with RBPMS silencing in Hec1A cell. These molecules are involved in pathways such as molecular mechanisms of cancer, estrogen receptor signaling, and senescence pathway. While estrogen-regulated changes were prominent in early stage low-grade EC, the identification of additional signaling changes provide support for an ongoing trial of levonorgestrel IUD + everolimus (mTOR inhibitor) and can be probed further to identify new targets for combination conservative management strategies. Additionally, biomarkers from these pathways, such as RBPMS, can be studied to guide the selection of progestin-only therapy versus combination therapy. Citation Format: Qian Zhang, Xiaoping Su, Joseph Celestino, Ying Yuan, Samuel C. Mok, Karen H. Lu, Melinda S. Yates. Compartment-specific profiling for evaluation of disrupted signaling in early stage, low-grade endometrial cancer [abstract]. In: Proceedings of the AACR Virtual Special Conference: Endometrial Cancer: New Biology Driving Research and Treatment; 2020 Nov 9-10. Philadelphia (PA): AACR; Clin Cancer Res 2021;27(3_Suppl):Abstract nr PO049.