MUTANT ALPHA-SUBUNIT OF G(Z) TRANSFORMS SWISS 3T3 CELLS

Many hormones and neurotransmitters induce cell proliferation by regul ating signaling pathways controlled by heterotimeric G proteins. Mutat ions that activate the alpha subunits of G(s) and G(i2) produce the gs p and gip2 oncogenes that are found in certain human endocrine tumors. Similar mutations have conferred on other G alpha subunits the abilit y to promote neoplastic transformation in cultured mammalian cells, G( z), a G protein whose normal signaling function is poorly understood, shares with G(i2) the ability to inhibit adenylyl cyclase. We asked wh ether mutationally activated alpha(z) can stimulate cell proliferation in a cell line in which stimulation adenylyl cyclase is mitogenic, Sw iss 3T3 cells, Stable expression of alpha(z)-Q205L in Swiss 3T3 cells induced focus formation, a faster growth rate with a higher saturation density, anchorage-independent growth in soft agar, and increased [H- 3]thymidine incorporation in the absence of growth factors. alpha(z)-Q 205L produced a similar but less extensively transformed phenotype in NIH3T3 cells-increased saturation density in culture, a smaller number of foci and few colonies in soft agar. Stimulation of thymidine incor poration by alpha(z)-Q205L in Swiss 3T3 cells was increased by co-trea tment with cholera toxin, a stimulator of adenylyl cyclase. Taken toge ther, our results indicate that a(z) stimulates one or more mitogenic pathways in Swiss 3T3 cells, and that effectiveness of these mitogenic pathways does not require reducing the concentration of cellular cAMP .