Fascin-1 expression is associated with neuroendocrine prostate cancer and directly suppressed by androgen receptor

BACKGROUND

Neuroendocrine prostate cancer (NEPC) is an aggressive form of prostate cancer, arising from resistance to androgen-deprivation therapies. However, the molecular mechanisms associated with NEPC development and invasiveness are still poorly understood. Here we investigated the expression and functional significance of Fascin-1 (FSCN1), a pro-metastasis actin-bundling protein associated with poor prognosis of several cancers, in neuroendocrine differentiation of prostate cancer.

METHODS

Differential expression analyses using Genome Expression Omnibus (GEO) database, clinical samples and cell lines were performed. Androgen or antagonist's cellular treatments and knockdown experiments were used to detect changes in cell morphology, molecular markers, migration properties and in vivo tumour growth. Chromatin immunoprecipitation-sequencing (ChIP-Seq) data and ChIP assays were analysed to decipher androgen receptor (AR) binding.

RESULTS

We demonstrated that FSCN1 is upregulated during neuroendocrine differentiation of prostate cancer in vitro, leading to phenotypic changes and NEPC marker expression. In human prostate cancer samples, FSCN1 expression is restricted to NEPC tumours. We showed that the androgen-activated AR downregulates FSCN1 expression and works as a transcriptional repressor to directly suppress FSCN1 expression. AR antagonists alleviate this repression. In addition, FSCN1 silencing further impairs in vivo tumour growth.

CONCLUSION

Collectively, our findings identify FSCN1 as an AR-repressed gene. Particularly, it is involved in NEPC aggressiveness. Our results provide the rationale for the future clinical development of FSCN1 inhibitors in NEPC patients.

AXL confers cell migration and invasion by hijacking a PEAK1-regulated focal adhesion protein network

Aberrant expression of receptor tyrosine kinase AXL is linked to metastasis. AXL can be activated by its ligand GAS6 or by other kinases, but the signaling pathways conferring its metastatic activity are unknown. Here, we define the AXL-regulated phosphoproteome in breast cancer cells. We reveal that AXL stimulates the phosphorylation of a network of focal adhesion (FA) proteins, culminating in faster FA disassembly. Mechanistically, AXL phosphorylates NEDD9, leading to its binding to CRKII which in turn associates with and orchestrates the phosphorylation of the pseudo-kinase PEAK1. We find that PEAK1 is in complex with the tyrosine kinase CSK to mediate the phosphorylation of PAXILLIN. Uncoupling of PEAK1 from AXL signaling decreases metastasis in vivo, but not tumor growth. Our results uncover a contribution of AXL signaling to FA dynamics, reveal a long sought-after mechanism underlying AXL metastatic activity, and identify PEAK1 as a therapeutic target in AXL positive tumors.

AXL receptor tyrosine kinase has a role in metastasis but the mechanism is unclear. In this study, the authors show that AXL activation can control focal adhesion dynamics via PEAK1 and that AXL-mediated PEAK1 phosphorylation is required for metastasis of triple negative breast cancer cells in vivo.

TMPRSS2:ERG gene fusion expression regulates bone markers and enhances the osteoblastic phenotype of prostate cancer bone metastases

Prostate cancers have a strong propensity to metastasize to bone and promote osteoblastic lesions. TMPRSS2:ERG is the most frequent gene rearrangement identified in prostate cancer, but whether it is involved in prostate cancer bone metastases is largely unknown. We exploited an intratibial metastasis model to address this issue and we found that ectopic expression of the TMPRSS2:ERG fusion enhances the ability of prostate cancer cell lines to induce osteoblastic lesions by stimulating bone formation and inhibiting the osteolytic response. In line with these in vivo results, we demonstrate that the TMPRSS2:ERG fusion protein increases the expression of osteoblastic markers, including Collagen Type I Alpha 1 Chain and Alkaline Phosphatase, as well as Endothelin-1, a protein with a documented role in osteoblastic bone lesion formation. Moreover, we determined that the TMPRSS2:ERG fusion protein is bound to the regulatory regions of these genes in prostate cancer cell lines, and we report that the expression levels of these osteoblastic markers are correlated with the expression of the TMPRSS2:ERG fusion in patient metastasis samples. Taken together, our results reveal that the TMPRSS2:ERG gene fusion is involved in osteoblastic lesion formation induced by prostate cancer cells.

TMPRSS2-ERG fusion promotes prostate cancer metastases in bone

Bone metastasis is the major deleterious event in prostate cancer (PCa). TMPRSS2-ERG fusion is one of the most common chromosomic rearrangements in PCa. However, its implication in bone metastasis development is still unclear. Since bone metastasis starts with the tropism of cancer cells to bone through specific migratory and invasive processes involving osteomimetic capabilities, it is crucial to better our understanding of the influence of TMPRSS2-ERG expression in the mechanisms underlying the bone tropism properties of PCa cells. We developed bioluminescent cell lines expressing the TMPRSS2-ERG fusion in order to assess its role in tumor growth and bone metastasis appearance in a mouse model. First, we showed that the TMPRSS2-ERG fusion increases cell migration and subcutaneous tumor size. Second, using intracardiac injection experiments in mice, we showed that the expression of TMPRSS2-ERG fusion increases the number of metastases in bone. Moreover, TMPRSS2-ERG affects the pattern of metastatic spread by increasing the incidence of tumors in hind limbs and spine, which are two of the most frequent sites of human PCa metastases. Finally, transcriptome analysis highlighted a series of genes regulated by the fusion and involved in the metastatic process. Altogether, our work indicates that TMPRSS2-ERG increases bone tropism of PCa cells and metastasis development.

Estrogen related receptor alpha in castration-resistant prostate cancer cells promotes tumor progression in bone

Bone metastases are one of the main complications of prostate cancer and they are incurable. We investigated whether and how estrogen receptor-related receptor alpha (ERRα) is involved in bone tumor progression associated with advanced prostate cancer. By meta-analysis, we first found that ERRα expression is correlated with castration-resistant prostate cancer (CRPC), the hallmark of progressive disease. We then analyzed tumor cell progression and the associated signaling pathways in gain-of-function/loss-of-function CRPC models in vivo and in vitro. Increased levels of ERRα in tumor cells led to rapid tumor progression, with both bone destruction and formation, and direct impacts on osteoclasts and osteoblasts. VEGF-A, WNT5A and TGFβ1 were upregulated by ERRα in tumor cells and all of these factors also significantly and positively correlated withERRα expression in CRPC patient specimens. Finally, high levels of ERRα in tumor cells stimulated the pro-metastatic factor periostin expression in the stroma, suggesting that ERRα regulates the tumor stromal cell microenvironment to enhance tumor progression. Taken together, our data demonstrate that ERRα is a regulator of CRPC cell progression in bone. Therefore, inhibiting ERRα may constitute a new therapeutic strategy for prostate cancer skeletal-related events.

Abstract 694: Axon guidance neuropilin and plexin A2 genes are involved in ERG-associated prostate cancer

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.

Abstract 1691: TMPRSS2:ERG fusion enhances osteoblastic phenotype of prostate cancer bone metastases

Background: Bone metastases are the major cause of morbidity and mortality in prostate cancer (PCa) patients. Recently, TMPRSS2:ERG gene fusions produced by rearrangements along chromosome 21 was found in more than 50% of PCa samples, resulting in androgen-dependent aberrant expression of the functional ERG transcription factor. Interestingly, ERG transcription factor has been previously shown to be involved in bone development. This study is therefore focused on investigating whether TMPRSS2:ERG gene fusions are involved in PCa bone metastasis development.

Methods: We previously established cell clones overexpressing TMPRSS2:ERG from two PCa cell lines, PC3 and PC3c. We first studied induced bone lesion phenotype using in vivo intra-tibial injection models. Secondly, we analyzed transcriptional changes induced by ERG transcription factors in PC3c clones to identify potential target genes. Then, direct target genes were further validated and investigated in vitro using RT-qPCR, ELISA, siRNA and ChIP techniques. Importantly, using a cohort of prostate carcinoma samples, we validated the expression correlation between ERG and its target target genes expression in human pathology.

Results: Bone lesions induced in vivo by intra-tibial injections of PC3 or PC3c cells are known to be osteolytic or mixed (osteoblastic/osteolytic) respectively. Interestingly, intra-tibial injections of PC3c clones expressing the fusion showed a statistically significant increase of osteoblastic phenotype compared to control cells. Furthermore, intra-tibial injections of PC3 clones expressing the fusion showed a strong decrease of osteolytic phenotype, reinforcing our previous result in PC3c clones.

Among the genes identified by transcriptomic study and dysregulated in PC3c clones expressing the fusion, we have identified the ERG candidate target Endothelin-1 (ET-1), which is known to be involved in osteoblast proliferation and in osteoblastic metastasis formation in PCa. Indeed, we found that ET-1 expression was up-regulated in PC3c-TMPRSS2:ERG clones, and the up-regulation was dependent on ERG expression levels. Importantly, silencing of ERG resulted in decreased expression of ET-1. In silico analysis of the promoter of ET-1 revealed the presence of several potential binding sites of ERG. ChIP experiments followed by qPCR demonstrated a direct binding to one of them. Moreover, in human PCa samples, there was a significant expression correlation between ET-1 and fusion gene TMPRSS2:ERG, reinforcing the direct functional link between ET-1 and the fusion in PCa.

Conclusion: Taken together, these results strongly suggest that the TMPRSS2:ERG gene fusion contributes to the osteoblastic phenotype of PCa bone metastases and ET-1 is one of the involved factors, directly regulated by the transcription factor ERG.

Citation Format: Carine Delliaux, Tian V. Tian, Mathilde Bouchet, Anaïs Fradet, Nathalie Vanpouille, Anne Flourens, Rachel Deplus, Xavier Leroy, Yvan de Launoit, Edith Bonnelye, Martine Duterque-Coquillaud. TMPRSS2:ERG fusion enhances osteoblastic phenotype of prostate cancer bone metastases. [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 1691.