Expression of a Cx43 deletion mutant in 3T3 A31 fibroblasts prevents PDGF-induced inhibition of cell communication and suppresses cell growth

Communication through gap junctions was first suggested to have a role in t he social control of cell growth over 30 years ago. However, despite extens ive experimentation, the importance of gap junctions as a general mechanism of growth control remains to be established. A number of different studies have shown that a common early response of cells in culture to polypeptide growth factors such as PDGF is a rapid and transient inhibition of cell co mmunication suggesting that a cell may have to lose communication with its neighbors before it can undergo cell division. Here we show that 3T3 A31 fi broblasts exposed to PDGF exhibit a 50% decrease in cell communication as m easured by dye transfer in the absence of significant changes in the cellul ar content and distribution of Cx43. Likewise, PDGF inhibited cell communic ation in cells transfected either with a vector which did not contain a cDN A or with an expression vector encoding full-length Cx43 fused to a c-myc t ag (Cx43-M). In contrast, 3T3 A31 fibroblasts transfected with an expressio n construct encoding a deletion mutant of Cx43 (Cx43-256M) consisting of am ino acids 1-256 of Cx43 fused to a c-myc tag maintain high levels of gap ju nction activity following exposure to PDG;F. These results suggest that sit es which trigger loss of cell communication in response to PDGF are located within amino acids 257 to 382 of the Cx43 molecule. Cells transfected with an expression vector encoding full-length Cx43 fused to a c-myc tail exhib ited a reduced basal growth rate compared to both parent cells and cells tr ansfected with a control vector but maintained a strong mitogenic response to PDGF. In contrast, both the basal growth rate and the mitogenic response to PDGF was markedly reduced in cells which expressed Cx43-256M consistent with the hypothesis that loss of cell communication is required before a c ell can respond to mitogenic stimuli. (C) 1999 Academic Press.