INFLUENCE OF ELEVATED EXPRESSION OF RAT WILD-TYPE PMP22 AND ITS MUTANT PMP22(TREMBLER) ON CELL-GROWTH OF NIH3T3 FIBROBLASTS

The peripheral myelin gene PMP22 is the rat and human homologue of the murine growth-arrest-specific gene gas3. The biological function of P MP22 is unknown, but recent progress in the analysis of rat Schwann ce lls expressing altered levels of PMP22 revealed that one role of PMP22 is as a negative growth modulator. We have investigated the influence of rat PMP22 (rPMP22) and a mutant of PMP22 (rPMP22(Tr)) resembling t he murine trembler mutation on cell growth of retrovirus-vector-infect ed mouse NIH3T3 cells. Transduced cells carrying the two different sen se constructs expressed rPMP22 and rPMP22(Tr) mRNAs and proteins. Elev ated levels of rPMP22 and rPMP22(Tr) significantly reduced fibroblast growth as judged by proliferation assays. Despite a negative modulator y influence of rPMP22 and rPMP22(Tr) on cell proliferation, cell cycle analyses by flow cytometry did not reveal an influence of rPMP22 or r PMP22(Tr) on the synchronous progression of resting NIH3T3 cells from G(0) into S phase. However, cell cycle analyses by flow cytometry of a synchronously dividing cultures demonstrated that the expression of rP MP22 and rPMP22(Tr) increased the fraction of cells in the G(1) phase of the cell cycle. Furthermore, cell death analyses revealed that, in contrast to control cells and cells carrying the rPMP22(Tr) construct, a significantly increased fraction of NIH3T3 cells expressing rPMP22 exit the proliferation compartment showing hallmarks of programmed cel l death. These results indicate that (i) rPMP22 and rPMP22(Tr) act as negative modulators of proliferation in murine fibroblasts probably th rough extension of the G(1) phase of the cell cycle and (ii) rPMP22 bu t not rPMP22(Tr) promotes programmed death of these cells.