Functional membrane androgen receptors in colon tumors trigger pro-apoptotic responses in vitro and reduce drastically tumor incidence in vivo

Abstract

BackgroundMembrane androgen receptors (mAR) have been implicated in the regulation of cell growth, motility and apoptosis in prostate and breast cancer. Here we analyzed mAR expression and function in colon cancer.ResultsUsing fluorescent mAR ligands we showed specific membrane staining in colon cell lines and mouse xenograft tumor tissues, while membrane staining was undetectable in healthy mouse colon tissues and non-transformed intestinal cells. Saturation/displacement assays revealed time- and concentration-dependent specific binding for testosterone with a KD of 2.9 nM. Stimulation of colon mAR by testosterone albumin conjugates induced rapid cytoskeleton reorganization and apoptotic responses, even in the presence of anti-androgens. The actin cytoskeleton drug cytochalasin B effectively inhibited the pro-apoptotic responses and caspase-3 activation. Interestingly, in vivo studies revealed that mAR activation resulted in a 65% reduction of tumor incidence in chemically induced Balb/c mice colon tumors.ConclusionOur results demonstrate for the first time that functional mARs are predominantly expressed in colon tumors and that their activation results in induction of anti-tumor responses in vitro and extensive reduction of tumor incidence in vivo.

Testosterone induced apoptosis in colon cancer cells is regulated by PI3K/Rac1 signaling

“…Based on previous titration experiments 12 we have used a 10 27 mol l 21 testosterone-HSA concentration for mAR stimulation throughout this study. Caco2 human colon cancer cells are cultured in DMEM (Invitrogen Biochrom KG, Berlin, Germany) supplemented with 25 mmol l 21 HEPES, 4.5 g l 21 glucose, L-glutamin, 10% fetal bovine serum (Biochrom KG) and 1% antibiotics.…”

“…This stock solution was incubated for 30 min at room temperature with 0.3% charcoal and 0.03% dextran, centrifuged at 3000g and passed through a 0.45-mm filter to remove any potential contamination with free steroid. 12 Earlier binding studies in prostate and colon cancer cells established the optimal concentration of testosterone-HSA treatments. 2,12,16 Accordingly, testosterone-HSA solution was used at a final concentration of 10 27 mol l 21 throughout the study.…”

“…4,5,[9][10][11] Functional membrane androgen binding sites have been also reported in colon cancer cells and tissues. 12,13 Their activation by testosterone conjugates induced potent pro-apoptotic responses. 12 and inhibition of the migration potential.…”

“…12,13 Their activation by testosterone conjugates induced potent pro-apoptotic responses. 12 and inhibition of the migration potential. 13,14 Moreover, experimental evidence was provided indicating that both, the pro-apoptotic steroid action and the inhibition of the migration potential were independent of the classical androgen receptors signaling.…”

“…13,14 Moreover, experimental evidence was provided indicating that both, the pro-apoptotic steroid action and the inhibition of the migration potential were independent of the classical androgen receptors signaling. [12][13][14] Interestingly, it was further reported that these effects were regulated by a mechanism involving actin reorganization. 13,14 In a recent study, we have described the signaling pathway governing the mAR-induced effects on actin restructuring in colon tumor cells.…”