Abstract 4571: Semaphorin/plexin signalling promotes nucleocytoplasmic trafficking of nuclear receptors

Abstract

Abstract Androgen receptor (AR) signalling is critical to prostate cancer progression and androgen deprivation therapy (ADT) is the first line of treatment for metastatic prostate cancer. Acquired resistance to ADT results from androgen-independent reactivation of the AR pathway primarily. Prostate tumours also bypass androgen blockade by the upregulation of the glucocorticoid receptor (GR). Both AR and GR are nuclear receptors that bind their respective ligands in the cytoplasm and then translocate to the nucleus where they act as transcription factors. Plexins are cell surface receptors for semaphorins. PlexinB1 is overexpressed and mutated in several cancers including prostate cancer and deletion of the plexinB1 gene reduces metastasis in mouse models, indicating an oncogenic role for plexinB1 in prostate cancer. We have found that activation of plexinB1 by semaphorin4D (Sema4D) results in AR phosphorylation at serine 81, activation of AR-transcriptional activity and increased expression of androgen-responsive genes, effects reversed by plexinB1 knockdown. PlexinB1 activation increases the translocation of both AR-GFP constructs and endogenous AR to the nucleus in prostate cancer cells. Furthermore knockdown of AR in the prostate cancer cell line LNCaP reduces Sema4D-induced anchorage-independent growth of these cells. To determine if the Sema4D/plexinB1 signalling pathway also affects translocation of other nuclear receptors to the nucleus, we have also studied the effect of Sema4D treatment on nuclear trafficking of the glucocorticoid receptor (GR). Prostate cancer cells were transfected with a GR-GFP construct and the subcellular localisation of GR-GFP was monitored upon Sema4D treatment by immunocytochemistry and confocal microscopy. The nuclear translocation of endogenous GR was also assessed following Sema4D stimulation by immunocytochemistry and subcellular fractionation studies. We found that activation of plexinB1 by Sema4D results in a significant increase in the percentage of cells with nuclear GR-GFP and in the nuclear localisation of endogenous GR in prostate cancer cells. These findings show that plexinB1 activation has a role in the trafficking and activation of nuclear receptors and so may have a role in resistance to ADT in late stage prostate cancer. Citation Format: Magali Williamson, John R. Masters. Semaphorin/plexin signalling promotes nucleocytoplasmic trafficking of nuclear receptors. [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 4571.