Post-Transcriptional Regulation of Connexin43 in H-Ras-Transformed Cells

Abstract

Connexin43 (Cx43) expression is lost in cancer cells and many studies have reported that Cx43 is a tumor suppressor gene. Paradoxically, in a cellular NIH3T3 model, we have previously shown that Ha-Ras-mediated oncogenic transformation results in increased Cx43 expression. Although the examination of transcriptional regulation revealed essential regulatory elements, it could not solve this paradox. Here we studied post-transcriptional regulation of Cx43 expression in cancer using the same model in search of novel gene regulatory elements. Upon Ras transformation, both Cx43 mRNA stability and translation efficiency were increased. We investigated the role of Cx43 mRNA 3′ and 5′Untranslated regions (UTRs) and found an opposing effect; a 5′UTR-driven positive regulation is observed in Ras-transformed cells (NIH-3T3Ras), while the 3′UTR is active only in normal NIH-3T3Neo cells and completely silenced in NIH-3T3Ras cells. Most importantly, we identified a previously unknown regulatory element within the 3′UTR, named S1516, which accounts for this 3′UTR-mediated regulation. We also examined the effect of other oncogenes and found that Ras- and Src-transformed cells show a different Cx43 UTRs post-transcriptional regulation than ErbB2-transformed cells, suggesting distinct regulatory pathways. Next, we detected different patterns of S1516 RNA-protein complexes in NIH-3T3Neo compared to NIH-3T3Ras cells. A proteomic approach identified most of the S1516-binding proteins as factors involved in post-transcriptional regulation. Building on our new findings, we propose a model to explain the discrepancy between the Cx43 expression in Ras-transformed NIH3T3 cells and the data in clinical specimens.

Connexin and pannexin channels in cancer

“…The downreguation of cyclin-dependent kinase 6 by miRNA-124-3p transferred between glioblastoma cells via gap junctions promotes the anti-proliferative effect [ 71 ]. The different mechanism involving post-transcriptional regulation of Cx43 is recently reported in H-Ras-transformed cells compared to non-transformed parental cells; 5′untranslated region (UTR) is active in Ras-transferred NIH-3 T3 cells while the 3′UTR is active in normal, non-transformed NIH-3 T3 cell and a regulatory element in the 3′UTR was identified [ 72 ]. This study suggests specific regulatory mechanisms in regulation of connexin expression in cancer cells.…”

Pathological Implications of Cx43 Down-regulation in Human Colon Cancer

“…Besides having junctional properties, Cx43 is also an important player in regulating cell growth and differentiation (Araya et al, 2005), with an established tumor suppressive properties (Kandouz et al, 2013).…”

Specific functional pathologies of Cx43 mutations associated with oculodentodigital dysplasia

“…Previously we examined another mutation in this same domain (D3N) and found that human fibroblasts exhibited a lower expression of Cx43 and impaired Cx43 function ( Churko et al ., 2011b ; Esseltine et al ., 2015 ). Of interest, both D3N and L7V mutants are located in the N-terminal domain, and both mutants lead to reduced Cx43 RNA levels, which suggests that this part of the sequence is important for Cx43 RNA transcription and/or stability and may be affected by important regulatory elements ( Kandouz et al ., 2013 ; Oyamada et al ., 2013 ). L7V-expressing fibroblasts can deliver low levels of Cx43 to the cell surface, where they may contribute to increased (“leaky”) ATP release and form few gap junction channels.…”