Androgen-regulated Formation and Degradation of Gap Junctions in Androgen-responsive Human Prostate Cancer Cells

Abstract

The constituent proteins of gap junctions, called connexins (Cxs), have a short half-life. Despite this, the physiological stimuli that control the assembly of Cxs into gap junctions and their degradation have remained poorly understood. We show here that in androgen-responsive human prostate cancer cells, androgens control the expression level of Cx32-and hence the extent of gap junction formation-post-translationally. In the absence of androgens, a major fraction of Cx32 is degraded presumably by endoplasmic reticulum-associated degradation, whereas in their presence, this fraction is rescued from degradation. We also show that Cx32 and Cx43 degrade by a similar mechanism. Thus, androgens regulate the formation and degradation of gap junctions by rerouting the pool of Cxs, which normally would have been degraded from the early secretory compartment, to the cell surface, and enhancing assembly into gap junctions. Androgens had no significant effect on the formation and degradation of adherens and tight junction-associated proteins. The findings that in a cell culture model that mimics the progression of human prostate cancer, degradation of Cxs, as well as formation of gap junctions, are androgen-dependent strongly implicate an important role of junctional communication in the prostate morphogenesis and oncogenesis.

The Carboxyl Tail of Connexin32 Regulates Gap Junction Assembly in Human Prostate and Pancreatic Cancer Cells

“…We further showed that androgens, the key players that govern prostate morphogenesis and oncogenesis (17), regulated the formation and degradation of gap junctions by controlling the expression level of Cx32 posttranslationally (18). In these studies we had fortuitously observed that the retrovirally expressed cytoplasmic tail-deleted Cx32 appeared to assemble into small gap junctions compared with those formed by the expression of the full-length Cx32 (18). Moreover, our previous study with cadherin-null human squamous carcinoma cells had also shown that the assembly of Cx32 into gap junctions was facilitated when cells acquired a partially polarized state and that the cytoplasmic tail of Cx32 (abbreviated as Cx32-CT) was required to initiate the formation of a gap junction plaque and/or its subsequent growth in these cells (19).…”

“…Our previous studies showed that the retrovirus-mediated expression of Cx32 in Cx-null, androgensensitive prostate cancer cell line, LNCaP, induced the formation of gap junctions, restored junctional communication, inhibited growth in vitro, and retarded malignancy in vivo (16). We further showed that androgens, the key players that govern prostate morphogenesis and oncogenesis (17), regulated the formation and degradation of gap junctions by controlling the expression level of Cx32 posttranslationally (18). In these studies we had fortuitously observed that the retrovirally expressed cytoplasmic tail-deleted Cx32 appeared to assemble into small gap junctions compared with those formed by the expression of the full-length Cx32 (18).…”

Tyrosine phosphatase TC-PTP directly interacts with connexin43 to regulate gap junction intercellular communication

“…The Triton X-100 solubility assay was modified from a method described previously (Mitra et al, 2006). LA-25 cells grown in 10-cm Petri dishes were rinsed three times with PBS and scraped into 1 ml of lysis buffer (50 mM Tris-HCl pH 7.4, 1 mM EGTA, 1 mM EDTA, 1 mM PMSF, 100 mM NaCl, half a tablet of complete protease inhibitor per 25 ml of buffer, 5 mM NaF and 5 mM Na 3 VO 4 ).…”

Connexins and Cadherin Cross-talk in the Pathogenesis of Prostate Cancer

“…To produce recombinant retrovirus for infection of target cells, amphotropic PTi67 cells were infected with the transiently produced recombinant retrovirus from EcoPack and selected in G418 (400 μg/ml). The recombinant retrovirus produced from the pooled polyclonal cultures of PTi67 cells was assayed for the virus titer by colony forming units as described [17][18][19][20][21][22].…”