TPA induced expression and function of human connexin 26 by post-translational mechanisms in stably transfected neuroblastoma cells

Connexin 26 (Cx26) has been proposed to be a tumor suppressor gene and its expression may modulate development, cell growth and differentiation in var ious tissues, including the brain. 12-O-tetradecanoylphorbol-13-acetate (TP A) may serve as either tumor promoter (in mammary gland amd skin) or as a d ifferentiating agent (in neuroblastoma and leukemic cells) and may also mod ulate expression, function and phosphorylation of gap junctions. In this st udy, to determine the effects of TPA on Cx26 expression and its function in neuroblastoma, we transfected N2A mouse neuroblastoma cells (which are gap junction deficient) with the coding region of human Cx26 gene (which lacks TPA response elements) and examined the changes of expression and function of Cx26 following 10 nM TPA treatment. Individual clones of transfectants stably expressed distinct levels of exogenous Cx26 as judged by Northern an d Western blots, immunocytochemistry and electrophysiological recordings. C x26 channels displayed unitary conductances of about 140-155 pS. Increase o f Cx26 expression following TPA treatment was markedly observed using immun ocytochemistry and Western blots of membrane fractions although it was not detected in Northern or Western blots of whole cells. This increase in Cx26 expression in the plasma membrane was accompanied by an increase of functi on as evidenced in measurements of junctional conductance. These results su ggest that induction of exogenous Cx26 in neuroblastoma cells by TPA treatm ent is controlled by post-translational mechanisms.