Activation of Membrane Androgen Receptors in Colon Cancer Inhibits the Prosurvival Signals Akt/Bad In Vitro and In Vivo and Blocks Migration via Vinculin/Actin Signaling

Abstract

Recently, we reported that membrane androgen receptors (mARs) are expressed in colon tumors triggering strong apoptotic responses. In the present study, we analyzed mAR-induced downstream effectors controlling cell survival and migration of Caco2 colon cancer cells. We show that long-term activation of mAR downregulated the activity of PI-3K and Akt and induced dephosphorylation/activation of the proapoptotic Bad (p-Bad). Moreover, treatment of APC Min/+ mice, which spontaneously develop intestinal tumors, with mAR-activating testosterone conjugates reduced the tumor incidence by 80% and significantly decreased the expression of p-Akt and p-Bad levels in tumor tissue. Furthermore, mAR activation strongly inhibited Caco2 cell migration. In accordance with these findings, vinculin, a protein controlling cell adhesion and actin reorganization, was effectively phosphorylated upon mAR activation. Phosphorylation inhibitors genistein and PP2 inhibited actin reorganization and restored motility. Moreover, silencing vinculin by appropriate siRNA's, or blocking actin reorganization by cytochalasin B, restored the migration potential. From these results we conclude that mAR activation inhibits the prosurvival signals Akt/Bad in vitro and in vivo and blocks migration of colon cancer cells via regulation of vinculin signaling and actin reorganization, supporting the powerful tumoristatic effect of those receptors.

GDNF increases cell motility in human colon cancer through VEGF–VEGFR1 interaction

“…Conclusively, therefore, GDNF directs cell migration by the interaction of VEGF and VEGFR1. Signaling molecules, including ERK, p38, JNK, and Akt, have been demonstrated to play important roles in colon cancer cell invasion and migration (Tremblay et al 2006, Lai et al 2010, Gu et al 2011, Tomas et al 2012. The activation of Ret by GDNF results in the activation of the MAP kinase pathways (van Weering & Bos 1997).…”

“…Previous studies and our recent report demonstrated that GDNF activates MAP kinase, and that Akt exerts biological and pathophysiological functions (Tremblay et al 2006, Lai et al 2010, Gu et al 2011, Tomas et al 2012. Thus, we examined whether MAP kinase and the Akt signaling pathway are involved in GDNF-induced VEGF expression and colon cancer migration.…”

Membrane Androgen Receptor Down-Regulates c-Src-Activity and Beta-Catenin Transcription and Triggers GSK-3beta-Phosphorylation in Colon Tumor Cells

“…Recently we have reported the expression of functional mARs in colon tumor cells and tissues and have addressed their biological effects [9,10]. Using non-permeable androgen derivatives (testosterone albumin conjugates, TAC) that do not bind to iAR in colon tumor cells [9,10,11], it was shown that mAR activation triggered rapid non-genomic signaling that regulated various cellular responses including actin reorganization, apoptosis and migration.…”

“…Recently we have reported the expression of functional mARs in colon tumor cells and tissues and have addressed their biological effects [9,10]. Using non-permeable androgen derivatives (testosterone albumin conjugates, TAC) that do not bind to iAR in colon tumor cells [9,10,11], it was shown that mAR activation triggered rapid non-genomic signaling that regulated various cellular responses including actin reorganization, apoptosis and migration. In particular, it was shown that rapid activation of the FAK/mTOR/p70S6K/PAK1 cascade governs the early actin cytoskeleton rearrangements [11], while vinculin phosphorylation, in association with morphological alterations of the focal adhesions, accounts for the inhibition of colon tumor cell migration [10].…”

“…Using non-permeable androgen derivatives (testosterone albumin conjugates, TAC) that do not bind to iAR in colon tumor cells [9,10,11], it was shown that mAR activation triggered rapid non-genomic signaling that regulated various cellular responses including actin reorganization, apoptosis and migration. In particular, it was shown that rapid activation of the FAK/mTOR/p70S6K/PAK1 cascade governs the early actin cytoskeleton rearrangements [11], while vinculin phosphorylation, in association with morphological alterations of the focal adhesions, accounts for the inhibition of colon tumor cell migration [10]. In line with the observed potent pro-apoptotic responses, late down-regulation of the pro-survival PI-3K/Akt signaling activity was observed in colon tumor cells and tissues treated with TAC [10].…”