Rab Protein Family Research Articles

Rab3B Proteins: Cellular Functions, Regulatory Mechanisms, and Potential as a Cancer Therapy Target.

RAB3 proteins, a pivotal subgroup within the Rab protein family, are known to be highly expressed in brain and endocrine gland tissues, with detectable levels also observed in exocrine glands, adipose tissue, and other peripheral tissues. They play an indispensable role in the trafficking of cellular products from the endoplasmic reticulum (ER) to the Golgi apparatus and ultimately to secretory vesicles, participating in vesicle transport, mediating cell membrane adhesion, and facilitating membrane fusion during exocytosis. Among these, Rab3B, a specific subtype of RAB3, is a low-molecular-weight (approximately 25 kD) GTP-binding protein (GTPase) characterized by its typical GTPase fold, composed of seven β-strands (six parallel and one antiparallel) surrounded by six α-helices. Previous studies have proved the significant roles of Rab3B in vesicle transport and hormone trafficking. However, its involvement in cancer remains largely unexplored. This review aims to dig into the potential mechanisms of Rab3B in various cancers, including hepatocellular cancer, lung adenocarcinoma, pancreatic cancer, breast cancer, prostate cancer, neuroblastoma and cervical cancer. Given its pivotal functions and underexplored status in oncology, Rab3B stands out as a promising target for both diagnosis and therapy in cancer treatment, with investigations into its biological mechanisms in tumorigenesis offering significant potential to advance future diagnostic and therapeutic strategies across various malignancies.

Transport mechanisms between the endocytic, recycling, and biosynthetic pathways via endosomes and the trans-Golgi network.

After the endocytic and biosynthetic pathway converge, they partially share the route to the lysosome/vacuole. Similarly, the endocytic recycling and secretory pathways also partially share the route to the plasma membrane. The interaction of these transport pathways is mediated by endosomes and the trans-Golgi network (TGN), which act as sorting stations in endocytic and biosynthesis pathway, and endosomes has a bidirectional transport to and from the TGN. In mammalian cells endosomes can be largely classified as early/sorting, late, and recycling endosomes, based on their morphological features and localization of Rab family proteins, which are key factors in vesicular trafficking. However, these endosomes do not necessarily represent specific compartments that are comparable among different species. For instance, Rab5 localizes to early endosomes in mammalian cells but is widely localized to early-to-late endosomes in yeast, and to pre-vacuolar endosomes and the TGN in plant cells. The SNARE complexes are also key factors widely conserved among species and localized specifically to the endosomal membrane, but the localization of respective homologs is not necessarily consistent among species. These facts suggest that endosomes should be classified more inclusively across species. Here we reconsider the mammalian endosome system based on findings in budding yeast and other species and discuss the differences and similarities between them.

The small GTPase RAB-18 is involved in regulating development/diapause by recruiting the intestinal cholesterol transporter NCR-1 onto the apical side in Caenorhabditis elegans

RAB family proteins, which are small GTPases, are integral to the process of eukaryotic membrane trafficking. In the nematode, Caenorhabditis elegans, 31 RAB proteins have been identified through genome sequencing. Using an RNAi screen specifically targeting C. elegans rab genes, we identified multiple genes that are involved in the regulation of larval development, in particular, the rab-18 gene. Our molecular genetic studies resulted in several findings. First, RAB-18 predominantly functions in the intestine to regulate larval development by modulating steroid hormone signaling. Second, the C. elegans cholesterol transporter NCR-1 is a target of RAB-18 in the intestine. Third, the membrane trafficking of NCR-1 to the apical side in intestinal cells is particularly influenced by RAB-18. Finally, RAB-18 and NCR-1 possibly co-localize on membrane vesicles. Our study is the first to demonstrate the relationship between a RAB protein and a cholesterol transporter, in which the RAB protein probably drives the transporter to the apical membrane in the intestine to regulate cholesterol uptake. This study provides insight into the molecular mechanisms underlying human disease stemming from a transport defect of cholesterol and its derivative.

Biophysical Evidence for the Amyloid Formation of a Recombinant Rab2 Isoform of Leishmania donovani.

The most fatal form of Visceral leishmaniasis or kala-azar is caused by the intracellular protozoan parasite Leishmania donovani. The life cycle and the infection pathway of the parasite are regulated by the small GTPase family of Rab proteins. The involvement of Rab proteins in neurodegenerative amyloidosis is implicated in protein misfolding, secretion abnormalities and dysregulation. The inter and intra-cellular shuttlings of Rab proteins are proposed to be aggregation-prone. However, the biophysical unfolding and aggregation of protozoan Rab proteins is limited. Understanding the aggregation mechanisms of Rab protein will determine their physical impact on the disease pathogenesis and individual health. This work investigates the acidic pH-induced unfolding and aggregation of a recombinant Rab2 protein from L. donovani (rLdRab2) using multi-spectroscopic probes. The acidic unfolding of rLdRab2 is characterised by intrinsic fluorescence and ANS assay, while aggregation is determined by Thioflavin-T and 90⁰ light scattering assay. Circular dichroism determined the secondary structure of monomers and aggregates. The aggregate morphology was imaged by transmission electron microscopy. rLdRab2 was modelled to be a Rab2 isoform with loose globular packing. The acidinduced unfolding of the protein is a plausible non-two-state process. At pH 2.0, a partially folded intermediate (PFI) state characterised by ~ 30% structural loss and exposed hydrophobic core was found to accumulate. The PFI state slowly converted into well-developed protofibrils at high protein concentrations demonstrating its amyloidogenic nature. The native state of the protein was also observed to be aggregation-prone at high protein concentrations. However, it formed amorphous aggregation instead of fibrils. To our knowledge, this is the first study to report in vitro amyloid-like behaviour of Rab proteins in L donovani. This study provides a novel opportunity to understand the complete biophysical characteristics of Rab2 protein of the lower eukaryote, L. donovani.

High Expression of TBC1 Domain Family Member 22A is Related to Poor Prognosis in Ovarian Serous Cystadenocarcinoma.

Objective: TBC1 domain family member 22A (TBC1D22A) possesses GTPase-activating protein (GAP) activity of Rab family proteins and has not been reported in ovarian serous cystadenocarcinoma (OSC). The research was designed to evaluate the expression and prognostic effect of TBC1D22A in OSC. Methods: TCGA, GTEx, GEO, HPA, and GDSC databases were adopted to explore the oncogenic mechanism of TBC1D22A in OSC, as well as the correlation between TBC1D22A and patient prognosis, IC50, stemness index, immune checkpoint, and immune infiltration. To compare the occurrence of end-point times, Kaplan-Meier survival curves were used. Independent prognostic factors of patients with OSC were analyzed with both univariate as well as multivariate Cox regression analyses, and the overall survival (OS) of the patients at 1, 2 and 3 years was predicted with nomograms. Results: TB1D22A expression was elevated in OSC, and high expression of TBC1D22A was related to poor OS, progression free survival (PFS), disease specific survival (DSS), and disease-free survival (DFS) in OSC. TBC1D22A had predictive value in both univariate and multivariate Cox regression analysis. TBC1D22A was positively correlated with M2 macrophage infiltration and the expression of most immune checkpoint genes. IC50 for cisplatin and paclitaxel increased in patients with overexpression of TBC1D22A. Conclusion: TBC1D22A is an independent prognostic risk factor for patients of ovarian cancer. Future research is required to fully understand the carcinogenic mechanism and clinical utility of TBC1D22A in ovarian cancer.

Fluconazole-Induced Protein Changes in Osteogenic and Immune Metabolic Pathways of Dental Pulp Mesenchymal Stem Cells of Osteopetrosis Patients.

Osteopetrosis is a rare inherited disease caused by osteoclast failure, resulting in increasing bone density in humans. Patients with osteopetrosis possess several dental and cranial complications. Since carbonic anhydrase II (CA-II) deficiency is a major cause of osteopetrosis, CA-II activators might be an attractive potential treatment option for osteopetrosis patients. We conducted comprehensive label-free quantitative proteomics analysis on Fluconazole-treated Dental Pulp Mesenchymal Stem/Stromal Cells from CA-II-Deficient Osteopetrosis Patients. We identified 251 distinct differentially expressed proteins between healthy subjects, as well as untreated and azole-treated derived cells from osteopetrosis patients. Twenty-six (26) of these proteins were closely associated with osteogenesis and osteopetrosis disease. Among them are ATP1A2, CPOX, Ap2 alpha, RAP1B and some members of the RAB protein family. Others include AnnexinA1, 5, PYGL, OSTF1 and PGAM4, all interacting with OSTM1 in the catalytic reactions of HCO3 and the Cl- channel via CAII regulation. In addition, the pro-inflammatory/osteoclast regulatory proteins RACK1, MTSE, STING1, S100A13, ECE1 and TRIM10 are involved. We have identified proteins involved in osteogenic and immune metabolic pathways, including ERK 1/2, phosphatase and ATPase, which opens the door for some CA activators to be used as an alternative drug therapy for osteopetrosis patients. These findings propose that fluconazole might be a potential treatment agent for CAII- deficient OP patients. Altogether, our findings provide a basis for further work to elucidate the clinical utility of azole, a CA activator, as a therapeutic for OP.

Pathogenic LRRK2 compromises the subcellular distribution of lysosomes in a Rab12-RILPL1-dependent manner.

Mutations in leucine-rich repeat kinase 2 (LRRK2) cause familial Parkinson's disease (PD). Recent studies have shown that LRRK2 physiologically phosphorylates several Rab family proteins including Rab12 and that this phosphorylation is accelerated by the pathogenic mutations in LRRK2, although the significance in the PD pathogenesis remains unknown. Here we examined the effect of the overexpression of LRRK2 on the distribution of organelles in cultured cells and found that lysosomes become clustered in a perinuclear region upon the overexpression of pathogenic mutant LRRK2 in a manner dependent on its kinase activity. The perinuclear clustering of lysosomes was abolished by knocking out RAB12 as well as its effector protein RILPL1. Re-expression of Rab12 in RAB12 knockout cells suggested that the phosphorylation at Ser106 of Rab12 is required for the perinuclear clustering of lysosomes. Moreover, phosphorylated Rab12 was also accumulated on the clustered lysosomes, and the phosphorylation of Rab12 increased its interaction with RILPL1, leading us to conclude that the increase in the phosphorylation of Rab12 by pathogenic LRRK2 compromised intracellular lysosomal transport via the enhanced interaction of Rab12 with RILPL1. These data suggest the involvement of abnormal regulation of lysosomal transport in the LRRK2-mediated pathogenesis of PD.

The Small GTPase Rab14 Regulates the Trafficking of Ceramide from Endoplasmic Reticulum to Golgi Apparatus and Facilitates Classical Swine Fever Virus Assembly.

Classical swine fever virus (CSFV) is a highly pathogenic RNA virus belonging to the Flaviviridae family that can cause deadly classical swine fever (CSF) in pigs. However, the molecular details of virus replication in the host are still unclear. Our previous studies have reported that several Rab proteins mediate CSFV entry into host cells, but it is unknown whether CSFV hijacks other Rab proteins for effective viral infection. Here, we systematically studied the role of Rab14 protein in regulating lipid metabolism for promoting viral assembly. First, Rab14 knockdown and overexpression significantly affected CSFV replication, indicating the essential role of Rab14 in CSFV infection. Interestingly, Rab14 could significantly affect virus replication in the late stage of infection. Mechanistically, CSFV NS5A recruited Rab14 to the ER, followed by ceramide transportation to the Golgi apparatus, where sphingomyelin was synthesized. The experimental data of small molecule inhibitors, RNA interference, and replenishment assay showed that the phosphatidylinositol-3-kinase (PI3K)/AKT/AS160 signaling pathway regulated the function of Rab14 to affect the transport of ceramide. More importantly, sphingomyelin on the Golgi apparatus contributed to the assembly of viral particles. Blockage of the Rab14 regulatory pathway induced the reduction of the content of sphingomyelin on the Golgi apparatus, impairing the assembly of virus particles. Our study clarifies that Rab14 regulates lipid metabolism and promotes CSFV replication, which provides insight into a novel function of Rab14 in regulating vesicles to transport lipids to the viral assembly factory. IMPORTANCE The Rab protein family members participate in the viral replication of multiple viruses and play important roles in the virus infection cycle. Our previous research focused on Rab5/7/11, which regulated the trafficking of vesicles in the early stage of CSFV infection, especially in viral endocytosis. However, the role of other Rab proteins in CSFV replication is unclear and needs further clarification. Strikingly, we screened some Rabs and found the important role of Rab14 in CSFV infection. Virus infection mobilized Rab14 to regulate the vesicle to transport ceramide from the ER to the Golgi apparatus, further promoting the synthesis of sphingomyelin and facilitating virus assembly. The treatment of inhibitors showed that the lipid transport mediated by Rab14 was regulated by the PI3K/AKT/AS160 signaling pathway. Knockdown of Rab14 or the treatment with PI3K/AKT/AS160 inhibitors reduced the ceramide content in infected cells and hindered virus assembly. Our study is the first to explain that vesicular lipid transport regulated by Rab promotes CSFV assembly, which is conducive to the development of antiviral drugs.

Impaired hepatic autophagy exacerbates hepatotoxin induced liver injury

Hepatotoxins activate the hepatic survival pathway, but it is unclear whether impaired survival pathways contribute to liver injury caused by hepatotoxins. We investigated the role of hepatic autophagy, a cellular survival pathway, in cholestatic liver injury driven by a hepatotoxin. Here we demonstrate that hepatotoxin contained DDC diet impaired autophagic flux, resulting in the accumulation of p62-Ub-intrahyaline bodies (IHBs) but not the Mallory Denk-Bodies (MDBs). An impaired autophagic flux was associated with a deregulated hepatic protein-chaperonin system and significant decline in Rab family proteins. Additionally, p62-Ub-IHB accumulation activated the NRF2 pathway rather than the proteostasis-related ER stress signaling pathway and suppressed the FXR nuclear receptor. Moreover, we demonstrate that heterozygous deletion of Atg7, a key autophagy gene, aggravated the IHB accumulation and cholestatic liver injury. Conclusion: Impaired autophagy exacerbates hepatotoxin-induced cholestatic liver injury. The promotion of autophagy may represent a new therapeutic approach for hepatotoxin-induced liver damage.

Tissue specific LRRK2 interactomes reveal a distinct striatal functional unit.

Mutations in LRRK2 are the most common genetic cause of Parkinson's disease. Despite substantial research efforts, the physiological and pathological role of this multidomain protein remains poorly defined. In this study, we used a systematic approach to construct the general protein-protein interactome around LRRK2, which was then evaluated taking into consideration the differential expression patterns and the co-expression behaviours of the LRRK2 interactors in 15 different healthy tissue types. The LRRK2 interactors exhibited distinct expression features in the brain as compared to the peripheral tissues analysed. Moreover, a high degree of similarity was found for the LRRK2 interactors in putamen, caudate and nucleus accumbens, thus defining a potential LRRK2 functional cluster within the striatum. The general LRRK2 interactome paired with the expression profiles of its members constitutes a powerful tool to generate tissue-specific LRRK2 interactomes. We exemplified the generation of the tissue-specific LRRK2 interactomes and explored the functions highlighted by the "core LRRK2 interactors" in the striatum in comparison with the cerebellum. Finally, we illustrated how the LRRK2 general interactome reported in this manuscript paired with the expression profiles can be used to trace the relationship between LRRK2 and specific interactors of interest, here focusing on the LRRK2 interactors belonging to the Rab protein family.

Endocytosis of dopamine receptor: Signaling in brain.

This chapter describes the physiological significance of dopamine receptor endocytosis and the consequence of the receptor signaling. Endocytosis of dopamine receptors is regulated by many components such as clathrin, β-arrestin, caveolin, and Rab family proteins. The dopamine receptors escape from lysosomal digestion, and their recycling occurs rapidly, reinforcing the dopaminergic signal transduction. In addition, the pathological impact of the receptors interacting with specific proteins has been the focus of much attention. Based on this background, this chapter provides an in-depth understanding of the mechanisms of molecules interacting with dopamine receptors and discusses the potential pharmacotherapeutic targets for α-synucleinopathies and neuropsychiatric disorders.

Ultrasound-assisted green synthesis of triazole-based azomethine/thiazolidin-4-one hybrid inhibitors for cancer therapy through targeting dysregulation signatures of some Rab proteins

ABSTRACT The overexpression of Rab proteins was linked to cancer development, making this family of proteins an attractive drug target for the identification of novel inhibitors against tumor diseases. In this study, novel triazole-based azomethine/thiazolidin-4-one hybrid analogs were designed, prepared and structurally confirmed by using elemental and spectral techniques, these include FT-IR, MS, and NMR spectra. In addition, in vitro cytotoxic activity was assessed against NCI-60 cancer cell lines. To understand the possible mode of action and drugability, molecular docking studies and drug-likeness were achieved. The docking simulations were performed against various Rab family proteins Rab2a, Rab25, Rab5, and Rab35; promising targets for cancer medication to support the cytotoxicity findings and to further validate the action of new molecules. Furthermore, in silico ADMET screening of the molecules was within the recommended values stated by Lipinski's rule of five (Ro5), indicating their oral bioavailability and therapeutic potentials. Among the newly prepared analogs tested, compounds 4d and 3d exhibited significant antitumor activity against breast, ovarian, lung, and leukemia cancer cell lines. Our findings suggested that azomethine/thiazolidin-4-one moieties incorporated triazole analogs are a promising class of molecular entities for the development of new anticancer therapies, through targeting of some Rab proteins.

Membrane Fusion and SNAREs: Interaction with Ras Proteins.

The superfamily of Ras proteins comprises different molecules belonging to the GTPase family. They normally cycle between an active state bound to GTP which activates effectors while the protein is membrane-associated, and an inactive GDP-bound state. They regulate the intracellular trafficking and other cellular processes. The family of Rab proteins includes several members and they have been found, among other Ras proteins, to be fundamental for important biological processes, such as endocytosis and exocytosis. SNARE proteins control the fusion of vesicles by forming quaternary complexes which are divided into two small groups on the two different compartments. Generally, the association of three SNARE proteins on the donor compartment with the one on the target compartment determines the formation of the SNARE complex, the opening of the fusion pore and the formation of one single bigger vesicle. Interestingly, novel interactions between other molecules involved in intracellular trafficking, endosomal fusion and maturation have recently been found, such as the interaction between invariant chain and the Qb SNARE vti1b, and more functional connections between Rab proteins and SNAREs are supposed to be fundamental for the regulation of membrane fusion.

Abstract 5718: Rab34 is downregulated in human prostate cancer tissue

Abstract Background: Rab34 encodes a protein belonging to the Rab family of proteins, which are small GTPases important in regulating signal transduction and cellular processes. A potential role of Rab34 in cancer has been suggested, but few studies have reported its function in human epithelial cancers. It was reported that prostate cancer (PCa) patients were more prone to biochemical recurrence when Rab34 was downregulated in PCa tissue compared with benign prostate tissue (BPT), being negatively associated with miR-148, a miRNA that increased the growth in cell lines and was up-regulated in PCa samples. Rab34 is a putative target gene for miR-9. We aimed to explore the Rab34 and miR-9 expression in PCa using a bioinformatic analysis, however, the mere presence of miRNA-binding sites is insufficient for predicting target regulation, and therefore, we also analyzed Rab34 expression in BPT and PCa tissues. Design: The expression of miR9-5p and Rab34 mRNA was explored in the tumor tissues of the Cancer Genome Atlas (TCGA) through the bioinformatics tools of the dbDEMC2 and GEPIA2 web servers, and additional evidence of miR-9/Rab34 interaction was sought in the miRTarBase of experimentally validated microRNA-target interactions. Two pathologists evaluated Rab34 immunohistochemical expression in localized PCa and BPT in a prostate tissue microarray. For each spot an H-score was obtained by microscopic assessment of epithelial cells with positive staining. Differences in Rab34 expression were found by comparing H-Scores between BPT and PCa tissues using Mann-Whitney test, a p value less than 0.05 was considered statistically significant. Results: The analysis of miR-9 and Rab34 expression in the TCGA showed that Rab34 has a diverse expression in tumor tissues, being downregulated in colon, rectum and PCa, and upregulated in lymphoma, leukemia and pancreatic adenocarcinoma. On the other hand, miR-9 was upregulated in PCa and downregulated in pancreatic adenocarcinoma. There were no experimental evidence supporting the miR-9/Rab34 interaction in PCa tissues from the miRTarBase. However, most of the breast cancer datasets showed a negative correlation in the expression of both genes. Rab34 expression at protein level was assessed in 123 tissue cores representing PCa, and 86 tissue cores representing BPT. In cores with PCa mean Rab34 expression was significantly lower than the mean Rab34 expression in cores with BPT (p less than 0.0001). There was a lower mean staining score in PCa (87.3, 95% CI: 73.78 - 100.9), compared to BPT (156.3, 95% CI: 144 - 168.5). Conclusions: Our study shows that Rab34 is downregulated in PCa tissue. These findings are in accordance to a previous report that associated its lower expression to worse prognosis and tumor recurrence. The downregulation of Rab34 in PCa tissue might be related to overexpression of its putative microRNA, miR-9. Additional studies to detect the in situ expression of miR-9 in PCa are in progress to validate these results. Citation Format: Ines Benedetti, Lia Barrios, Juan Rebollo. Rab34 is downregulated in human prostate cancer tissue [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5718.

The roles of Rab protein family in neurological diseases.

The intracellular membrane trafficking is a complicated pathway network. Rab GTPases are key regulators of membrane trafficking that are generally considered as specific markers and indicators of various organelles and membrane trafficking in endocytic and secretory pathways. Dysfunction in axonal and endosomal transport related to Rab proteins is one of the most important causes of neurodegenerative diseases. In this review, we mainly introduce how the Rab proteins change in different neurodegenerative diseases and their regulatory roles in the pathological mechanisms of related diseases. We also discuss the relationships between mitochondrial and glial cell dysfunctions and Rab proteins. Further exploration of the regulatory roles of Rab proteins will shed lights on revealing the pathogenic mechanisms of neurological diseases and providing potential targets for the early diagnosis and treatment of neurological diseases.

High expression of Rab31 confers a poor prognosis and enhances cell proliferation and invasion in oral squamous cell carcinoma.

Dysregulation of Rab proteins has been observed in various types of cancer. Ectopic expression of Rab31, a member of the Rab protein family, is involved in cancer development and progression. However, the specific role and potential molecular mechanism underlying the functions of Rab31 remain largely unknown. Therefore, the current study aimed to investigate the functions of Rab31 in the development of cancer. Human oral squamous cell carcinoma (OSCC) samples were examined to determine the expression profile of Rab31 and its association with the clinicopathological characteristics of patients with OSCC. Knockdown of Rab31 expression with short hairpin RNA was performed to analyze the functions of Rab31 in vitro and in vivo. The expression of Rab31 was significantly elevated in human OSCC samples compared with that in normal oral mucosal epithelial tissues, and high expression levels were associated with high pathological grades. Furthermore, positive expression of Rab31 was associated with a poor prognosis in patients with OSCC. In addition, knockdown of Rab31 expression suppressed OSCC cell proliferation and induced apoptosis compared with those in the control-transfected cells, which may have been caused by downregulated cyclin D1 and survivin expression and upregulated B-cell lymphoma 2 expression. The invasive ability of OSCC cells was also abrogated by Rab31 silencing compared with that in the control-transfected cells, which was associated with downregulated N-cadherin and matrix metalloproteinase-9 expression levels and upregulated levels of E-cadherin expression. Furthermore, silencing Rab31 in OSCC cell lines, when compared with the control-transfected cells, significantly reduced tumor growth and inhibited the expression of survivin, Ki-67 and N-cadherin in vivo. By contrast, the expression levels of E-cadherin were increased. Taken together, the results of the present study supported important roles for Rab31 in regulating OSCC cell proliferation, apoptosis and invasion and may facilitate the identification of a new therapeutic target for the treatment of OSCC.

Chronically shortened rod outer segments accompany photoreceptor cell death in Choroideremia.

X-linked choroideremia (CHM) is a disease characterized by gradual retinal degeneration caused by loss of the Rab Escort Protein, REP1. Despite partial compensation by REP2 the disease is characterized by prenylation defects in multiple members of the Rab protein family that are master regulators of membrane traffic. Remarkably, the eye is the only organ affected in CHM patients, possibly because of the huge membrane traffic burden of the post mitotic photoreceptors, which synthesise outer segments, and the adjacent retinal pigment epithelium that degrades the spent portions each day. In this study, we aimed to identify defects in membrane traffic that might lead to photoreceptor cell death in CHM. In a heterozygous null female mouse model of CHM (Chmnull/WT), degeneration of the photoreceptor layer was clearly evident from increased numbers of TUNEL positive cells compared to age matched controls, small numbers of cells exhibiting signs of mitochondrial stress and greatly increased microglial infiltration. However, most rod photoreceptors exhibited remarkably normal morphology with well-formed outer segments and no discernible accumulation of transport vesicles in the inner segment. The major evidence of membrane trafficking defects was a shortening of rod outer segments that was evident at 2 months of age but remained constant over the period during which the cells die. A decrease in rhodopsin density found in the outer segment may underlie the outer segment shortening but does not lead to rhodopsin accumulation in the inner segment. Our data argue against defects in rhodopsin transport or outer segment renewal as triggers of cell death in CHM.

Autophagy and metabolism.

Metabolism consists of diverse life-sustaining chemical reactions in living organisms. Autophagy is a highly conservative process that responds to various internal and external stresses. Both processes utilize surrounding resources to provide energy and nutrients for the cell. Autophagy progression may proceed to the degradative or secretory pathway determined by Rab family proteins. The former is a degradative and lysosome-dependent catabolic process that produces energy and provides nutrients for the synthesis of essential proteins. The degradative pathway also balances the energy source of the cell and regulates tissue homeostasis. The latter is a newly discovered pathway in which the autophagosome is fused with the plasma membrane. Secretory autophagy participates in diverse functions and diseases ranging from the spread of viral particles to cancer and neurodegenerative diseases. Aberrant metabolism in the body causes various metabolic syndromes. This review explores the relationships among autophagy, metabolism, and related diseases.

Increased RAB31 Expression in Cancer-Associated Fibroblasts Promotes Colon Cancer Progression Through HGF-MET Signaling.

RAB family proteins participate in the dynamic regulation of cellular membrane compartments and are dysregulated in a variety of tumor types, which may alter the biological properties of cancer cells such as proliferation, migration, and invasion. In our previous study, we found that Ras-related protein Rab-31 (RAB31) expression was increased in late-stage colorectal cancer (CRC). The role of RAB31 has never been investigated in CRC. In this study, we found that expression of RAB31 in the tumor stroma but not cancer cells of colon cancer predicted poor survival. RAB31 can be detected in primary cancer-associated fibroblasts (CAFs) and paired normal fibroblasts. Conditioned medium (CM) from RAB31 overexpressing CAFs significantly promoted migration of colon cancer cell lines in vitro and in vivo. This process may be mediated by paracrine action of hepatocyte growth factor (HGF), which was increased in the CM of RAB31-overexpressing CAFs. Blockade of HGF/MET signaling by drug inhibition, knockdown of mesenchymal to epithelial transition factor (MET) in RKO, or antibody neutralization of HGF abolished migration of RKO cells mediated by RAB31 expression in CAFs. We propose that in colon cancer, increased RAB31 expression in CAFs may contribute to tumor progression by regulating the secretion of HGF in the tumor stroma.

Abstract 1520: RAB31 triggers oxaliplatin resistance in colorectal cancer via epithelial-mesenchymal transition

Abstract Colorectal tumorigenesis during Epithelial-Mesenchymal transition (EMT) is associated with cancer metastasis and drug resistance. The small G-proteins family has been implicated in the regulation of cell cytoskeleton, cell movement, and vesicle transport. Small G-proteins family is divided into five main families. The Rab protein family is a member of the Ras superfamily of small G-proteins. We analyzed all probes of the Rab family members from microarray datasets and RNA-sequencing. We further calculated the EMT scores by using an algorithm. Our results showed that the RAB31 expression levels of the three probes are positively correlated with EMT score (Pearson rho=0.72, 0.71 and 0.68, respectively). Compared with other family members, RAB31 had most significantly value in colorectal cancer cell lines. We established several two-way model with cDNA and shRNAs of RAB31, respectively. Furthermore, we observed that the expression of epithelial type marker CDH1 was inhibited, and mesenchymal type markers SNAI1 and SNAI2 were upregulated in RAB31 overexpression models. Moreover, we found that the protein level of RAB31 was correlated with several clinicopathological parameters (N status, M status) and disease-free survival in tissue arrays through immunohistochemistry staining. According to The Cancer Genome Atlas Program (TCGA) and online meta-database, high RNA level of RAB31 was consistent in colorectal cancer (HR=1.38, n=466 and HR=1.29, n=482) and correlated with poor prognosis of patients. In addition, we identified that RAB31 may associated with IC50 of oxaliplatin and EGFR trafficking. We concluded that RAB31 regulates the sensitivity of oxaliplatin, an additional chemotherapy strategy and an independent prognostic factor for colorectal cancer. Citation Format: Chi-Long Chen, Yu-Chan Chang, Michael Hsiao. RAB31 triggers oxaliplatin resistance in colorectal cancer via epithelial-mesenchymal transition [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1520.