Abstract 694: Axon guidance neuropilin and plexin A2 genes are involved in ERG-associated prostate cancer
Authors: Turpin Anthony , Delliaux Carine , Tian Tian , Vanpouille Nathalie , Flourens Anne , Deplus Rachel , Leroy Xavier , de Launoit Yvan , Duterque-Coquillaud Martine 
Published: July 2016

Background: Bone metastases are frequent and severe complications of prostate cancer (PCa), the most common malignancy that affects men in Western countries. Recurrent gene fusions, involving the ERG gene and the androgen-regulated promoter of the TMPRSS2 gene, occur in over 50% of PCa. The abnormal over-expression of the ERG transcription factor disturbs prostate cell transcriptome. We previously identified a series of genes directly and positively regulated by the ERG-fusion in vitro and in vivo. Among them can be found Plexin A2 (PLXNA2), which is a semaphorin receptor family member involved in axon guidance and in many pathophysiological processes, including cancer and bone disorders. We showed that PLXNA2 is involved in TMPRSS2:ERG-mediated enhancements of PC3c cell migration and invasion. These results prompted us to look for genes functionally related to PLXNA2 and involved in ERG-associated PCa.

Methods: Using a PCa cell line (PC3c) stably over-expressing the TMPRSS2:ERG fusion, we first used Ingenuity Pathway Analysis® in silico studies to analyze transcriptomic results and identify axon guidance genes associated with ERG-fusion expression in PCa. Their expression was validated in stable clones by RT-PCR and Immunofluorescence. Secondly, using RNAs of a human PCa sample cohort, we performed qRT-PCR to detect and correlate candidate genes to fusion expression. Finally, to validate the relevance of the identified genes, using immunohistochemistry experiments, we studied the expression of these genes in tissue samples, including primary tumors and lymph nodes or bone metastases.

Results: Using transcriptomic analyzes and expression validation, we identified neuropilin (NRP1 and NRP2) genes, plexin and semaphorin genes deregulated by the ERG fusion expression in stable clones. In human samples, PLXNA2, NRP1 and NRP2 expression were strongly associated to PCa, and particularly to metastastic PCa. We established a significant correlation between both PLXNA2 and NRP1 gene expression and the presence of TMPRSS2-ERG fusion. At protein level, NRP1 and NRP2 were highly detected in human lymph nodes and bone metastasis samples. Since neuropilin proteins are known to interact with plexin to act as coreceptors for semaphorin ligands, protein colocalization in stable clones suggested a functional association of PLXNA2 and NRPs in tumor cells.

Conclusion: Taken together, our results reveal that TMPRSS2-ERG fusion gene expression is able to deregulate axon guidance genes such as NRP1 and PLXNA2 in PCa. Therefore, since the interaction between plexins and their NRP1 and 2 coreceptors often determines the functional specificity of their semaphorin ligand effects, we hypothesize that the ERG fusion expression imbalances the plexin/neuropilin/semaphorin signaling to contribute to PCa progression. These results reinforce the recent interest in targeting neuropilins for cancer therapy.

Citation Format: Anthony Turpin, Carine Delliaux, Tian Tian, Nathalie Vanpouille, Anne Flourens, Rachel Deplus, Xavier Leroy, Yvan de Launoit, Martine Duterque-Coquillaud. Axon guidance neuropilin and plexin A2 genes are involved in ERG-associated prostate cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 694.