StAR-related Lipid Transfer Research Articles

Phosphatidylcholine Transfer Protein OsPCTP Interacts with Ascorbate Peroxidase OsAPX8 to Regulate Bacterial Blight Resistance in Rice.

Rice phosphatidylcholine transfer protein (PCTP), which contains a steroidogenic acute regulatory protein-related lipid transfer (START) domain, responds to bacterial blight disease. Overexpression of OsPCTP quantitatively enhances resistance to pathogen in rice, whereas depletion of it has the opposite effect. Further analysis showed that OsPCTP physically interacts with OsAPX8, a ROS scavenging enzyme, and influences ascorbate peroxidase enzymatic activity in vivo. In addition, the expression of pathogenesis-related genes PR1a, PR1b and PR10 were significantly induced in OsPCTP-OE plants compared with that in wild-type plants ZH11. Taken together, these results suggested that OsPCTP mediates bacterial blight resistance in rice through regulating the ROS defense pathway.

Model Mechanism for Lipid Uptake by the Human STARD2/PC-TP Phosphatidylcholine Transfer Protein.

The human StAR-related lipid transfer domain protein 2 (STARD2), also known as phosphatidylcholine (PC) transfer protein, is a single-domain lipid transfer protein thought to transfer PC lipids between intracellular membranes. We performed extensive μs-long molecular dynamics simulations of STARD2 of its apo and holo forms in the presence or absence of complex lipid bilayers. The simulations in water reveal ligand-dependent conformational changes. In the 2 μs-long simulations of apo STARD2 in the presence of a lipid bilayer, we observed spontaneous reproducible PC lipid uptake into the protein hydrophobic cavity. We propose that the lipid extraction mechanism involves one to two metastable states stabilized by choline-tyrosine or choline-tryptophane cation-π interactions. Using free energy perturbation, we evaluate that PC-tyrosine cation-π interactions contribute 1.8 and 2.5 kcal/mol to the affinity of a PC-STARD2 metastable state, thus potentially providing a significant decrease of the energy barrier required for lipid desorption.

Arabidopsis PROTODERMAL FACTOR2 binds lysophosphatidylcholines and transcriptionally regulates phospholipid metabolism.

Plant homeodomain leucine zipper IV (HD-Zip IV) transcription factors (TFs) contain an evolutionarily conserved steroidogenic acute regulatory protein (StAR)-related lipid transfer (START) domain. While the START domain is required for TF activity, its presumed role as a lipid sensor is not clear. Here we used tandem affinity purification from Arabidopsis cell cultures to demonstrate that PROTODERMAL FACTOR2 (PDF2), a representative member that controls epidermal differentiation, recruits lysophosphatidylcholines (LysoPCs) in a START-dependent manner. Microscale thermophoresis assays confirmed that a missense mutation in a predicted ligand contact site reduces lysophospholipid binding. We additionally found that PDF2 acts as a transcriptional regulator of phospholipid- and phosphate (Pi) starvation-related genes and binds to a palindromic octamer with consensus to a Pi response element. Phospholipid homeostasis and elongation growth were altered in pdf2 mutants according to Pi availability. Cycloheximide chase experiments revealed a role for START in maintaining protein levels, and Pi starvation resulted in enhanced protein destabilization, suggesting a mechanism by which lipid binding controls TF activity. We propose that the START domain serves as a molecular sensor for membrane phospholipid status in the epidermis. Our data provide insights toward understanding how the lipid metabolome integrates Pi availability with gene expression.

Interspecies pregnancy between Ovis canadensis mexicana and Ovis aries with reduced placental P450scc expression and intrauterine growth restriction

The present study aimed to assess the steroidogenic process in the placenta of hybrids Ovis canadensis mexicana × Ovis aries, particularly, to determine the plasma lipid profile and the relative abundance of proteins related to the steroidogenesis, to elucidate in part the mechanism of progesterone deficiency in hybrids. Plasma lipoproteins and placental cholesterol were determined by dry chemical colorimetric assays. Steroidogenic acute regulatory protein (STARD1), StAR-related lipid transfer domain protein 3 (STARD3), cholesterol side-chain cleavage enzyme (P450ssc), and 3β-hydroxysteroid dehydrogenase (3β-HSD) were evaluated by Western blot. In addition, STARD3 was also investigated by immunohistochemical experiments in sheep placenta. Results indicated that cholesterol, low-density lipoprotein (LDL), high-density lipoprotein (HDL), and very low-density lipoprotein (VLDL) plasma levels were similar between hybrid and control pregnancy groups. Conversely, intracellular cholesterol was increased (P ˂ 0.05) in the placenta tissue of hybrids. No significant differences in the relative abundance of both STARD3, STARD1, and 3β-HSD enzyme were observed in the placenta of hybrids compared to control animals, while the relative abundance of cytochrome P450scc was lower in hybrids than in control animals (P = 0.0279). The presence of STARD3 was observed in the cytoplasmic and perinuclear regions of mononucleate and binucleate cells of the trophoblast in the sheep placenta. The significant decrease in the abundance of P450scc in hybrids’ placenta may explain the decrease in progesterone biosynthesis, which has been related to intrauterine growth restriction (IUGR) in these animals previously.

Abstract PO4-05-13: Expression of DLC1/STARD12 and variants in clinical breast cancer and implication in skeletal metastasis

Abstract Introduction: Deleted in Liver Cancer 1 Protein, DLC1, also known as StAR Related Lipid Transfer Domain Containing 12 (StarD12), is a known negative regulator of the Rho GTPases and at the cellular level regulates cell migration. DLC1 gene transcription produces multiple isoforms of the DLC1 protein. The present study examined the clinical and prognostic implications of DLC1 isoforms, DLC1/V1/V2/V3, in relationship with Rho GTPases in human breast cancer. Methods: Expression of three DLC1 isoforms was evaluated in a cohort of breast cancer tissues and against the clinical, pathological and clinical outcome of patients. DLC1 expression was also assessed and compared against Rho GTPases, including Rho and Rho GTP Dissociation Inhibitor (Rho GDI), in the same cohort. Results: DLC1/V3 had a significant impact on the overall survival of patients and high levels were linked to shorter survival (Hazard Ratio=3.551 (95%CI 1.332-9.471, p=0.011), a prediction that was independent of other factors in multivariate analysis. RUC analysis demonstrated a significant predictive value for bone metastasis with DLC1/V3 (RUC=0.714, p=0.020), showing a Hazard ratio of 9.0 (1.8-44.5, p=0.007). Similarly, high DLC1/V2 expression was also linked to a shorter overall survival (p=0.035). DLC1/V2 did not show a significant correlation with bone metastasis. In contrast to V3 and V2 variants, DLC1 had a marginal overall survival benefit for the patients, in that patients with high DLC1 had a longer survival (p=0.056). DLC1/V3 had a contrasting correlation with Rho-A (r=-0.203, p=0.015) and Rho-GDI-G (r=0.194, p=0.019) and the combined expression of DLC1/V3 and RhoA/Rho-GDI-G further identified patients with poorer clinical outcome. Conclusions: DLC1 and its variants have differing impacts on breast cancer; whereas DLC1 appears to be a tumour suppressive molecule, its variant isoform-3 was more oncogenic and a significant negative prognostic factor, together with its regulators Rho and Rho GDI. Citation Format: Binbin Cong, Jane Lane, Xiaoshan Cao, Tracey Martin, Robert E Mansel, Eleri Davies, Wen Jiang. Expression of DLC1/STARD12 and variants in clinical breast cancer and implication in skeletal metastasis [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO4-05-13.

Activity refinement of aryl amino acetamides that target the P. falciparum STAR-related lipid transfer 1 protein

Malaria is a devastating disease that causes significant morbidity worldwide. The development of new antimalarial chemotypes is urgently needed because of the emergence of resistance to frontline therapies. Independent phenotypic screening campaigns against the Plasmodium asexual parasite, including our own, identified the aryl amino acetamide hit scaffold. In a prior study, we identified the STAR-related lipid transfer protein (PfSTART1) as the molecular target of this antimalarial chemotype. In this study, we combined structural elements from the different aryl acetamide hit subtypes and explored the structure-activity relationship. It was shown that the inclusion of an endocyclic nitrogen, to generate the tool compound WJM-715, improved aqueous solubility and modestly improved metabolic stability in rat hepatocytes. Metabolic stability in human liver microsomes remains a challenge for future development of the aryl acetamide class, which was underscored by modest systemic exposure and a short half-life in mice. The optimized aryl acetamide analogs were cross resistant to parasites with mutations in PfSTART1, but not to other drug-resistant mutations, and showed potent binding to recombinant PfSTART1 by biophysical analysis, further supporting PfSTART1 as the likely molecular target. The optimized aryl acetamide analogue, WJM-715 will be a useful tool for further investigating the druggability of PfSTART1 across the lifecycle of the malaria parasite.

Protection of Membrane Contact Protein by the Methionine Sulfoxide Reductases.

In this News and Views, I discuss our recent publication that established how steroidogenic acute regulatory-related lipid transfer domain-3 (STARD3), a membrane contact protein situated at lysosomal membranes, plays a role in the detoxification of cholesterol hydroperoxide. STARD3's methionine residues can be oxidized to methionine sulfoxide by cholesterol hydroperoxide, after which methionine sulfoxide reductases reduce the methionine sulfoxide residues back to methionine. The reaction also results in the reduction of the cholesterol hydroperoxide to an alcohol. The cyclic oxidation and reduction of methionine residues in STARD3 at membrane contact sites creates a catalytically efficient mechanism for detoxification of cholesterol hydroperoxide during cholesterol transport, thus protecting membrane contact sites and the entire cell against the toxicity of cholesterol hydroperoxide.

Potential regulation of dietary lipophilic antioxidants by mitochondrial contact sites

BackgroundRecent evidence has brought the mitochondrial contact sites, in communication with other organelles, to the centre of interest in cellular metabolism because of their essential role in many events surrounding the homeostasis of the human organism, including mitohormesis. Scope and approachThese mitochondrial dynamic structures are particularly active in response to feeding, after which the complex metabolic processes that produce energy from macronutrients in the mitochondria are also the largest producers of reactive oxygen species. However, little is known about the potential role of the rich lipid-binding protein coat of the outer mitochondrial membrane and the membrane of other organelles at mitochondrial contact sites as a place for transient storage and mobilisation of lipophilic antioxidant micronutrients, where they could function to promote mitohormesis. This commentary aims to assess the extent to which some of these lipid-binding proteins at mitochondrial contact sites are able to regulate the disposition of some lipophilic dietary antioxidants, such as β-carotene. Key findingsIt is found that the mitochondrial lipid-binding protein steroidogenic acute regulatory (StAR)-related lipid transfer (START) domain 1 (STARD1), the endoplasmic reticulum lipid-binding protein ASTER (with a StAR-like domain), and the endosomal lipid-binding proteins stabilins (with multiple fasciclin-1 adhesion domains) could work together at mitochondrial contact sites to allow the compartmentalisation and distribution of β-carotene and other dietary lipophilic antioxidants, which could help maintain the state of mitochondrial resistance to oxidative distress in the context of a healthy diet. ConclusionsThe surface of the outer mitochondrial membrane at contact sites during mitochondrial dynamics may have the potential to act as a functional platform for lipophilic antioxidant micronutrients that can eventually be mobilised to cope with supraphysiological levels of reactive oxygen species.

Regional bias of tumor suppressor gene mutations of STARD8 and WNK2 in colon cancers

StAR-related lipid transfer domain protein 8 (STARD8), encoding a Rho-GTPase-activating protein, and WNK2, encoding a serine/threonine kinase are candidate tumor suppressor genes (TSGs) in human cancers. Inactivation of these genes that would promote cancer pathogenesis is largely unknown in colon cancer (CC). Our study addressed to address whether STARD8 and WNK2 genes are mutated in CC. STARD8 and WNK2 genes possess mononucleotide repeats in their exons, which could be the targets for frameshift mutations in cancers with high microsatellite instability (MSI-H). By single-strand conformation polymorphism (SSCP) analysis, we analyzed the repeated sequences in 140 CCs (95 CCs with MSI-H and 45 CCs with stable MSI (MSS)). By DNA sequencing, we found that five MSI-H CCs (5/95: 5.3%) harbored the frameshift mutations, whereas MSS CCs (0/45) did not. In addition, we detected regional heterogeneous frameshift mutations of these genes in four (25%) of 16 MSI-H CCs. In immunohistochemistry for WNK2, WNK2 expression in the MSI-H CCs was significantly lower than that in the MSS CCs. Our results for the mutation and expression indicate that STARD8 and WNK2 genes are altered at various levels (frameshift mutation, expression, and regional heterogeneity) in MSI-H CCs, which might play a role in the pathogenesis by inactivating their TSG functions.

PYCR1, BANF1, and STARD8 Expression in Gastric Carcinoma: A Clinicopathologic, Prognostic, and Immunohistochemical Study.

It will be important to understand the molecular pathways of gastric cancer (GC) occurrence and progression, thus detecting predictive and prognostic biomarkers of GC. Pyrroline-5-carboxylate reductase 1 (PYCR1) was upregulated in many cancers, suggesting its possible roles in carcinogenesis and tumor metastases. Barrier-of-autointegration factor 1 (BANF1) is a protein family that plays essential roles in maintaining the integrity of an intact cellular genome. Rho-GTPs are molecular switches that control many signal transduction pathways in normal cells, including 3 subgroups from 1 to 3 (DLC1-3). DLC-3, known as StAR-related lipid transfer domain protein 8 (STARD8), and its role in cancers were not sufficiently studied. The study aimed to investigate the significance of PYCR1, BANF1, and STARD8 protein expression in GC tissues and normal gastric mucosa retrieved from patients with GC to detect prognostic roles of expression. Specimens were collected from 100 patients with gastric carcinoma. After the application of the inclusion criteria of the study, we prepared 100 paraffin blocks from samples of the 100 included patients; each block included samples from gastric carcinoma and adjacent non-neoplastic gastric mucosa. We assessed the expression of PYCR1, BANF1, and STARD8 using immunohistochemistry in all studied samples. We followed patients for the detection of disease progression and survival rates. We correlate PYCR1, BANF1, and STARD8 expression with clinical, pathologic, and prognostic parameters. Overexpression of PYCR1 and BANF1 and decreased expression of STARD8 was found in gastric carcinoma tissues than adjacent non-neoplastic gastric mucosa ( P <0.001), and was positively associated with high grade ( P =0.006), depth of tumor invasion, presence of lymph nodes metastases and advanced stage ( P =0.001), high incidence of GC progression, recurrence, unfavorable disease-free survival ( P =0.003) and unfavorable overall survival rates ( P <0.001). Thus, it was revealed that; in univariate and multivariate analyses, levels of PYCR1, BANF1, and STARD8 are associated with the overall survival rate of GC patients. We showed that overexpression of PYCR1 and BANF1 and decreased expression of STARD8 in GC tissues was associated with poor prognosis and GC progression.

Loss of STARD13 contributes to aggressive phenotype transformation and poor prognosis in papillary thyroid carcinoma.

StAR Related Lipid Transfer Domain Containing 13 (STARD13) serves as a tumor suppressor and has been characterized in several types of malignancies. However, the role and the molecular mechanism of STARD13 in regulating the progression of papillary thyroid carcinoma (PTC) remain underexplored. The gene expression and clinical information of thyroid cancer were downloaded using "TCGAbiolinks" R package. Quantitative PCR and immunohistochemical staining were conducted to detect the expression of STARD13 in clinical tumor and adjacent non-tumor samples. Wound-healing assay, Transwell assay and 3D spheroid invasion assay were performed to evaluate the migratory and invasive capacities of PTC cells. Cell proliferation ability was determined by CCK-8 assay, colony formation assay and 5-ethynyl-2'-deoxyuridine (EdU) incorporation assay. The alterations of indicated proteins were detected by Western blotting. In the present study, we found that STARD13 was significantly underexpressed in PTC, which was correlated with poor prognosis. Downregulation of STARD13 might be due to methylation of promoter region. Loss-and gain-of-function experiments demonstrated that STARD13 impeded migratory and invasive capacities of PTC cells in vitro and in vivo. In addition, we found that STARD13 regulated the morphology of PTC cells and inhibited epithelial-mesenchymal transition (EMT). Our results suggest that STARD13 acts as a metastasis suppressor and might be a potential therapeutic target in PTC.

SUMO1 degrader induces ER stress and ROS accumulation through deSUMOylation of TCF4 and inhibition of its transcription of StarD7 in colon cancer.

Small molecule degraders of small ubiquitin-related modifier 1 (SUMO1) induce SUMO1 degradation in colon cancer cells and inhibits the cancer cell growth; however, it is unclear how SUMO1 degradation leads to the anticancer activity of the degraders. Genome-wide CRISPR-Cas9 knockout screen has identified StAR-related lipid transfer domain containing 7 (StarD7) as a critical gene for the degrader's anticancer activity. Here, we show that both StarD7 mRNA and protein are overexpressed in human colon cancer and its knockout significantly reduces colon cancer cell growth and xenograft progression. The treatment with the SUMO1 degrader lead compound HB007 reduces StarD7 mRNA and protein levels and increases endoplasmic reticulum (ER) stress and reactive oxygen species (ROS) production in colon cancer cells and three-dimensional (3D) organoids. The study further provides a novel mechanism of the compound anticancer activity that SUMO1 degrader-induced decrease of StarD7 occur through degradation of SUMO1, deSUMOylation and degradation of T cell-specific transcription 4 (TCF4) and thereby inhibition of its transcription of StarD7 in colon cancer cells, 3D organoids and patient-derived xenografts (PDX).

Domain swapping of the C-terminal helix promotes the dimerization of a novel ribonuclease protein from Mycobacterium tuberculosis.

Polyketide metabolism-associated proteins in Mycobacterium tuberculosis play an essential role in the survival of the bacterium, which makes them potential drug targets for the treatment of tuberculosis (TB). The novel ribonuclease protein Rv1546 is predicted to be a member of the steroidogenic acute regulatory protein-related lipid-transfer (START) domain superfamily, which comprises bacterial polyketide aromatase/cyclases (ARO/CYCs). Here, we determined the crystal structure of Rv1546 in a V-shaped dimer. The Rv1546 monomer consists of four α-helices and seven antiparallel β-strands. Interestingly, in the dimeric state, Rv1546 forms a helix-grip fold, which is present in START domain proteins, via three-dimensional domain swapping. Structural analysis revealed that the conformational change of the C-terminal α-helix of Rv1546 might contribute to the unique dimer structure. Site-directed mutagenesis followed by in vitro ribonuclease activity assays was performed to identify catalytic sites of the protein. This experiment suggested that surface residues R63, K84, K88, and R113 are important in the ribonuclease function of Rv1546. In summary, this study presents the structural and functional characterization of Rv1546 and supplies new perspectives for exploiting Rv1546 as a novel drug target for TB treatment.

O002 Expression of MLN64 (lymph node metastasis 64) gene transcript in clinical gastric cancer and relationship with the ERBB4

Abstract Introduction MLN64 (Lymph Node Metastasis 64, or STARD3 (StAR Related Lipid Transfer Domain Containing 3)) has a role in the progression of certain cancers including breast and prostate cancers and connected to the pattern of ERBB2 (Her2). The present study explored the expression of MLN64 in clinical gastric cancer in connection with the ERBB family. Methods A gastric cancer cohort (n=322) was tested for the expression profile of MLN64 along with the ERBB family members. Comparisons were made between clinical, pathological subgroups and the clinical outcome together with ERBB expression status. Results Gastric tumours expressed significantly raised levels of MLN64 than normal tissues (p=0.0012) and showed a stepwise increase with increased tumour grade and TNM staging. However, there was no significant difference between node negative and node positive tumours. MLN64 alone had a weak value in evaluating the overall (OS) and disease free (DFS) survival. Amongst the four ERBB family members, MLN64 had a significant correlation with ERBB4 (Her4) (p=0.004). Stratification of patients by ERBB4 expression status indicates that in patients with low ERBB4 tumours, MLN64 presents a significant factor in assessing both disease free (DFS) p=0.027) and overall survival (OS) (p=0.048). Similarly, MLN64 expression identified a subpopulation of node positive patients with a most adverse clinical outcome (p=0.009 for DFS and p=0.048 for OS). Conclusion MLN64 expression is an indicator for the disease progression and clinical outcome in gastric cancer. Together with the expression pattern of ERBB4, it makes a prognostic factor for the patients.

START domain-mediated nuclear translocation of Them1 regulates the expression of metabolic genes relative to thermogenesis in brown adipocytes

Thioesterase superfamily member 1 (Them1) is a long-chain fatty acyl-CoA thioesterase that is highly expressed in brown adipose tissue (BAT), where it limits energy expenditure. Them1 is comprised of tandem enzymatic domains and a C-terminal lipid-binding steroidogenic acute regulatory protein (StAR)-related lipid transfer (START) domain. Fatty acid binding to the START domain stabilizes the enzymatic domains and increases activity, whereas lysophosphatidylcholine (LPC) acts in the opposite manner. In brown adipocytes, Them1 localizes to puncta within the cytoplasm, but diffuses in response to β-adrenergic stimulation after which it is also found in the nucleus. The aim of this study was to determine the mechanism of Them1 nuclear trafficking and the metabolic consequences. METHODS: Identification of a putative nuclear localization signal (NLS) was determined by computational analysis. Full-length, NLS-deleted, or truncated Them1 cDNA constructs were cloned and linked to EGFP. Plasmid or adenoviral vectors were transfected into immortalized brown adipose cells (iBAs) that do not express Them1. Them1 was visualized by live cell confocal imaging via EGFP and with NucSpot nuclear staining. Signal quantification was performed with Imaris software. Them1 nuclear localization was evaluated in the presence or absence of norepinephrine (NE), leptomycin B, cycloheximide, or lipids that bind the START domain. Them1 nuclear localization was also quantified in BAT from mice treated with a β3-adrenergic receptor agonist, CL316,243. mRNA expression in iBAs expressing full-length or NLS-mutant Them1 in response to NE was determined by RNA-Seq. RESULTS: In the diffuse state, Them1 localized to the nucleus in a time-dependent manner. The NLS resides in a hinge region between the thioesterase domains and the START domain. Deletion of either the NLS or the START domain blocked nuclear targeting. Conversely, truncated Them1 containing only the START domain was targeted to the nucleus. Entry into the nucleus was balanced by trafficking out of the nucleus and new protein synthesis was not required, as evidenced by using leptomycin B to block nuclear efflux and cycloheximide to block protein synthesis, respectively. Incubation of NE-stimulated iBAs with LPC promoted nuclear Them1 translocation. Them1 protein was also detected in the nucleus of BAT from wild-type mice in response to CL administration. Nuclear Them1 localization in iBAs was associated with down-regulated mRNA expression of genes that control lipid and glucose metabolism during cold adaptation. CONCLUSIONS: Our data suggest that LPC generated during thermogenesis binds and destabilizes the START domain, leading to exposure of the NLS and nuclear trafficking of Them1 in response to β-adrenergic stimulation. Once inside the nucleus, Them1 regulates the transcription of lipid and glucose metabolic enzymes that are required for chronic cold adaptation. This work was supported by NIH DK103046 to DEC, SJH, and EAO This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Abstract 6259: Novel inhibitors of StAR related lipid transfer protein 5 inhibitors target plasma membrane lipid raft growth signaling

Abstract Background: Treatment of colorectal cancer (CRC) presents a major challenge due to chemotherapeutic resistance and recurrence, which are attributed to the presence of cancer stem cells (CSCs). Cholesterol metabolism is a critical regulator of CSCs. Lipid Rafts are cholesterol-rich microdomains in the plasma membrane (PM) that anchor various growth receptors tyrosine kinases (RTKs). STARD5 is a novel protein that helps transport cholesterol from the endoplasmic reticulum to the PM. We have identified specific small molecule inhibitors of the STARD5 which disrupt the lipid rafts, resulting in the inhibition of growth signaling pathways. Methods and Results: In-silico modeling studies using STARD5 crystal structure revealed 8 putative inhibitors (SD5i (A-H)). In vitro binding studies to determine secondary structural changes using circular dichroism spectroscopy revealed SD5iA and SD5iB as excellent STARD5 ligands. Both SD5iA and SD5iB caused a potent inhibition (IC50 0.3 -18 µM) of CSC-enriched 3D spheroids in 9 CRC cell lines representative of 3 consensus molecular subtypes. However, SD5iA but not SD5iB showed toxicity towards normal murine intestinal organoids at effective doses against CRC CSCs. Also, SD5iB enhanced cytotoxicity by oxaliplatin and panitumumab against CRC CSCs in HT-29 spheroids. Hence, SD5iB was advanced into in vivo studies. SD5iB caused no discernible toxicity in doses as high as 100 mg/kg in NCr nude mice at gross, serum chemistry, organ viability, or intestinal stem cell level (organoid formation). Subsequently, we generated s.c. xenograft using dual CSC marker sorted HT-29 cells and enriched them further with chemotherapy (5-fluorouracil and oxaliplatin weekly x 3) treatment followed by randomization to vehicle or SD5iB (100mg/kg i.p. 3/wk x 3 wks.). We observed xenograft growth inhibition and LGR5 expression in SD5iB-treated animals compared to vehicle controls. Mechanistically, we observed a decrease in free accessible PM cholesterol by SD5i measured by fluorescently tagged cholesterol-binding bacterial protein fALOD4 in HT-29 cells. Moreover, lipid raft staining (cholera toxin B staining) was significantly reduced in SD5iB-treated HT-29 cells compared to vehicle control using immunofluorescence. Further, lipid raft isolation was done by sucrose gradient ultracentrifugation to study the changes in the phosphorylation of RTKs SD5iB treatment in HT-29 spheroids resulted in decreased phosphorylation of EGFR, IGF1Rβ, and FGFR1 in isolated lipid rafts. Consequently, we observed a robust inhibition of ERK1/2 activation following SD5iB treatment compared to vehicle control. Conclusion: SD5i shows anti-CSC activity by targeting lipid-raft-driven growth factor signaling. Hence, STARD5 inhibitors represent a novel class of targeted therapy that will enhance the efficacy of FDA-approved therapies in CRC. Citation Format: Shoja Hajira, Chetna Sharon, Daniel RodriguezAgudo, Rio Boothelllo, Glenn Kellogg, Gregorio Gil, William Pandak, Bhaumik B. Patel. Novel inhibitors of StAR related lipid transfer protein 5 inhibitors target plasma membrane lipid raft growth signaling [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6259.

G protein-coupled receptor 35 attenuates nonalcoholic steatohepatitis by reprogramming cholesterol homeostasis in hepatocytes.

Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disease worldwide. Fat accumulation "sensitizes" the liver to insult and leads to nonalcoholic steatohepatitis (NASH). G protein-coupled receptor 35 (GPR35) is involved in metabolic stresses, but its role in NAFLD is unknown. We report that hepatocyte GPR35 mitigates NASH by regulating hepatic cholesterol homeostasis. Specifically, we found that GPR35 overexpression in hepatocytes protected against high-fat/cholesterol/fructose (HFCF) diet-induced steatohepatitis, whereas loss of GPR35 had the opposite effect. Administration of the GPR35 agonist kynurenic acid (Kyna) suppressed HFCF diet-induced steatohepatitis in mice. Kyna/GPR35 induced expression of StAR-related lipid transfer protein 4 (STARD4) through the ERK1/2 signaling pathway, ultimately resulting in hepatic cholesterol esterification and bile acid synthesis (BAS). The overexpression of STARD4 increased the expression of the BAS rate-limiting enzymes cytochrome P450 family 7 subfamily A member 1 (CYP7A1) and CYP8B1, promoting the conversion of cholesterol to bile acid. The protective effect induced by GPR35 overexpression in hepatocytes disappeared in hepatocyte STARD4-knockdown mice. STARD4 overexpression in hepatocytes reversed the aggravation of HFCF diet-induced steatohepatitis caused by the loss of GPR35 expression in hepatocytes in mice. Our findings indicate that the GPR35-STARD4 axis is a promising therapeutic target for NAFLD.

A conserved mechanism determines the activity of two pivotal transcription factors that control epidermal cell differentiation in Arabidopsis thaliana

The surface of plants is covered by the epidermis, which protects the plant’s body from the external environment and mediates inter-cell layer signaling to regulate plant development. Therefore, the manifestation of epidermal traits at a precise location is a prerequisite for their normal growth and development. In Arabidopsis thaliana, class IV homeodomain-leucine zipper transcription factors PROTODERMAL FACTOR2 (PDF2) and ARABIDOPSIS THALIANA MERISTEM LAYER1 (ATML1) play redundant roles in epidermal cell differentiation. Nevertheless, several pieces of evidence suggest that the activity and/or function of PDF2 and ATML1 are regulated differently. The role of the steroidogenic acute regulatory protein-related lipid transfer (START) domain of ATML1 in restricting this protein’s activity has been demonstrated; however, whether this lipid-dependent mechanism regulates PDF2 expression is unknown. In this study, we demonstrated that the START domains of PDF2 and ATML1, regulate protein turnover in a position-dependent manner and affect the dimeric proteins. Our results show that a conserved mechanism provides the basis for the functional redundancy of PDF2 and ATML1 in epidermal cell differentiation and that an unidentified regulatory layer specific to PDF2 or ATML1 is responsible for the difference in the activity and/or function of PDF2 and ATML1.

Identification of novel Plasmodium vivax proteins associated with protection against clinical malaria.

As progress towards malaria elimination continues, the challenge posed by the parasite species Plasmodium vivax has become more evident. In many regions co-endemic for P. vivax and Plasmodium falciparum, as transmission has declined the proportion of cases due to P. vivax has increased. Novel tools that directly target P. vivax are thus warranted for accelerated elimination. There is currently no advanced vaccine for P. vivax and only a limited number of potential candidates in the pipeline. In this study we aimed to identify promising P. vivax proteins that could be used as part of a subunit vaccination approach. We screened 342P. vivax protein constructs for their ability to induce IgG antibody responses associated with protection from clinical disease in a cohort of children from Papua New Guinea. This approach has previously been used to successfully identify novel candidates. We were able to confirm previous results from our laboratory identifying the proteins reticulocyte binding protein 2b and StAR-related lipid transfer protein, as well as at least four novel candidates with similar levels of predicted protective efficacy. Assessment of these P. vivax proteins in further studies to confirm their potential and identify functional mechanisms of protection against clinical disease are warranted.

Testosterone and steroidogenic genes in the male blue crab Callinectes sapidus and their relationship with insulin-like androgenic gland factor (IAG) and crustacean female sex hormone (CFSH)

The abundance of the blue crab, Callinectes sapidus, has been declining in the Chesapeake Bay, possibly due to reduced spawning stock and deteriorating habitat conditions. Callinectes female reproductive capacity, i.e., fertilization efficiency, may depend on the quality and number of sperm stored in the spermathecae. Understanding endocrine regulation in male development and reproduction is necessary. Sexual differentiation of decapod crustaceans is primarily regulated by the insulin-like androgenic gland factor (IAG) and crustacean female sex hormone (CFSH). This system contrasts with the vertebrates wherein testosterone (T) controls male reproduction, sexual differentiation, and sex-specific behavior and physiology. With earlier reports of T presence in some decapods, this work aimed to determine if the blue crab Callinectes sapidus males exhibit T and if the corresponding levels are related to IAG and CFSH transcripts. To this end, the IAG and CFSH transcripts are estimated in the androgenic glands (AG) and eyestalk ganglia of juvenile and adult males, respectively. The levels of IAG transcripts are significantly (p < 0.05) higher in adult AGs than in juveniles. However, this pattern contrasts with CFSH transcripts in the eyestalk ganglia with juveniles higher than adults. The levels of T in adult testis, posterior vas deferens, AG, and hemolymph are significantly (p < 0.05) higher than those in juveniles. The presence of authentic T is further confirmed by liquid chromatography with tandem mass spectrometry. The transcript levels of the following genes known to be involved in vertebrate steroidogenesis are determined: StAR-related lipid transfer protein 3 (StAR3); 3β-hydroxysteroid dehydrogenase (3βHSD); two isoforms of 17β-hydroxysteroid dehydrogenase 8 (17βHSD8); and, 5α-reductase (5α-red). StAR3 levels are significantly (p < 0.05) higher in adult testis, anterior vas deferens, and AG than in juveniles. In comparison, 5α-red levels in testis, anterior vas deferens, posterior vas deferens, and AG of adults are significantly (p < 0.05) lower than in juveniles. The 5α-red transcripts are localized in the spermatocytes and spermatids in the testis and AG cells in the AG using in situ hybridization. These results indicate that CFSH may suppress IAG expression; the levels of T may be related to the male reproductive activity; and a putative regulatory interaction among IAG, CFSH, and steroidogenic genes in T synthesis may present in decapod crustaceans.