ROBO1, a tumor suppressor and critical molecular barrier for localized tumor cells to acquire invasive phenotype: Study in African‐American and Caucasian prostate cancer models

Abstract

High-risk populations exhibit early transformation of localized prostate cancer (CaP) disease to metastasis which results in the mortality of such patients. The paucity of knowledge about the molecular mechanism involved in acquiring of metastatic behavior by primary tumor cells and non-availability of reliable phenotype-discriminating biomarkers are stumbling blocks in the management of CaP disease. Here, we determine the role and translational relevance of ROBO1 (an organogenesis-associated gene) in human CaP. Employing CaP-progression models and prostatic tissues of Caucasian and African-American patients, we show that ROBO1 expression is localized to cell-membrane and significantly lost in primary and metastatic tumors. While Caucasians exhibited similar ROBO1 levels in primary and metastatic phenotype, a significant difference was observed between tumor phenotypes in African-Americans. Epigenetic assays identified promoter methylation of ROBO1 specific to African-American metastatic CaP cells. Using African-American CaP models for further studies, we show that ROBO1 negatively regulates motility and invasiveness of primary CaP cells, and its loss causes these cells to acquire invasive trait. To understand the underlying mechanism, we employed ROBO1-expressing/ROBO1-C2C3-mutant constructs, immunoprecipitation, confocal-microscopy and luciferase-reporter techniques. We show that ROBO1 through its interaction with DOCK1 (at SH3-SH2-domain) controls the Rac-activation. However, loss of ROBO1 results in Rac1-activation which in turn causes E-Cadherin/β-catenin cytoskeleton destabilization and induction of cell migration. We suggest that ROBO1 is a predictive biomarker that has potential to discriminate among CaP types, and could be exploited as a molecular target to inhibit the progression of disease as well as treat metastasis in high-risk populations such as African-Americans.

Epigenetic analysis identifies factors driving racial disparity in prostate cancer

“…Epigenetic changes are an inherent genomic property that appears early during development or acquired during life due to exposure to certain environmental factors . Variations in methylation have also been reported among AA and CA ethnic groups, with studies suggesting the existence of race‐specific methylation differences at birth . Several studies have reported that hypermethylation of CpG is a predominant event occurring in PCa .…”

Coexpression and expression quantitative trait loci analyses of the angiogenesis gene-gene interaction network in prostate cancer

“…Further, the study suggested that ROBO1 is a promising biomarker to differentiate metastatic cases from early stage cases. ROBO1 acts like a natural inhibitor of metastasis; therefore, this protein provides an opportunity to develop novel therapies targeting ROBO1 for treating metastatic PCa (14). Regarding Fibulin 5 (FBLN5), it is one of the extracellular matrix (ECM) glycoproteins and interacts with many ECM components, such as laminin, elastin, endostatin, and fibronectin (43).…”

“…FBLN5 is consistently downregulated in prostate tumors in data from expression microarray and RT-PCR (13). A recent study suggested ROBO1 as a tumor suppressor in PCa (14). Several groups consistently reported an association between an overexpression of E2F1 , a cell cycle-specific transcription factor, with progression of PCa, especially PCa metastasis (15–18).…”

Membrane-type matrix metalloproteinases: expression, roles in metastatic prostate cancer progression and opportunities for drug targeting

“…Three important SNP-SNP interactions were identified, linking MT3-MMP to ROBO1, CSF-1 and EGFR. ROBO1 is a member of the roundabout immunoglobulin superfamily, and has been identified as playing key roles in prostate cancer progression [53] . It is cleaved by MMPs and translocates into the nucleus of cancer cells, which perhaps suggests a signalling role.…”