Regulation of colony-stimulating factor 1-induced proliferation by heterotrimeric Gi2 proteins.

Receptors for hematopoietic cytokines possess intrinsic tyrosine-kinases or are associated with tyrosine-kinases; interactions between metabolic pathways activated by tyrosine-kinases and heterotrimeric G proteins are suspected, but not yet proven. To investigate whether alteration of G protein function affects signal transduction of hematopoietic cytokines, we expressed mutant Gi2 proteins in BAC 1.2F5 cells, a murine macrophage cell line that is dependent from monocyte-macrophage colony-stimulating factor (CSF 1) for its proliferation. Mutations made in alpha subunits constitutively activate (alpha i2-Q205L) or inactivate (alpha i2-G204A) Gi2 heterotrimers. We show that expression of alpha i2-Q205L in BAC 1.2F5 cells does not induce independence from CSF 1, but reduces the cells' requirement in CSF 1, shortens the length of the G1 phase and the cell doubling time in response to CSF 1, and protects cells from death by apoptosis induced by CSF 1 withdrawal, exposure to H2O2 or heat shock, but not mitoxantrone. More importantly, expression of alpha i2-G204A, a dominant negative mutant, inhibits BAC 1.2F5 cell proliferation in response to CSF 1, increases the length of the G1 phase and the cell doubling time, and accelerates apoptotic cell death after withdrawal of CSF 1, exposure to H2O2 or heat shock. We conclude that the metabolic pathways regulated by Gi2 proteins and CSF 1 tyrosine-kinase receptors converge on a common effector necessary for the regulation of macrophage survival and proliferation.