Expression of GTPase-deficient G alpha 16 inhibits Swiss 3T3 cell growth.
Expression of the GTPase-deficient G alpha 16 polypeptide G alpha 16Q212L, a member of the Gq family of heterotrimeric G proteins, constitutively activated phospholipase C beta activity in Swiss 3T3 cells. Expression of G alpha 16Q212L appears to persistently stimulte a low level of protein kinase C activity which also increases protein kinase A activity in Swiss 3T3 cells. Growth of G alpha 16Q212L expressing cells was significantly inhibited relative to wild-type Swiss 3T3 cells. Bombesin-stimulated DNA synthesis was completely inhibited in G alpha 16Q212L expressing clones, whereas the growth responses to platelet-derived growth factor (PDGF) and serum were inhibited 50-80% relative to wild-type cells. In addition to the inhibition of cell growth, G alpha 16Q212L expression significantly inhibited the stimulation of protein kinase C, Raf-1, MEK, mitogen-activated protein kinase, phospholipase A2 activity, and Ca2+ mobilization in response to PDGF. In contrast, PDGF receptor activation of phospholipase C gamma, phosphatidylinositol 3-kinase, and Ras GTP loading was similar in wild-type and G alpha 16Q212L expressing clones. PDGF regulation of membrane ruffling and actin fiber assembly, responses mediated in part by phosphatidylinositol 3-kinase, were unaffected in G alpha 16Q212L expressing clones. The growth inhibitory action of G alpha 16Q212L expression in Swiss 3T3 cells is downstream of the initial SH2 domain-encoded signal transduction proteins regulated in response to PDGF receptor autophosphorylation. The findings demonstrate that constitutively activated G alpha 16Q212L persistently activates phospholipase C activity and effectively inhibits a subset of cytoplasmic signal transduction pathways involved in growth factor tyrosine kinase receptor stimulation of cell growth. G16/Gq-regulated signal transduction can acutely stimulate specific response pathways involved in mitogenesis; but persistent activation of G16/Gq-regulated effectors, including phospholipase C beta, inhibit tyrosine kinase-initiated mitogenesis. One role for G16/Gq response systems may be to modulate growth factor receptor signaling.
Division of Basic Sciences, National Jewish Center for Immunology and Respiratory Medicine, Denver, Colorado 80206.
N X
NX
Qian
M
M
Russell
A M
AM
Buhl
G L
GL
Johnson
D016475:3T3 Cells; D000818:Animals; D001769:Blood; D001839:Bombesin / Q000494:pharmacology; D002455:Cell Division / Q000187:drug effects; D004247:DNA / Q000096:biosynthesis; D004789:Enzyme Activation; D020558:GTP Phosphohydrolases / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000096:biosynthesis / Q000378:metabolism*; D051379:Mice; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology; D017479:Receptors, Platelet-Derived Growth Factor / Q000378:metabolism; D011994:Recombinant Proteins; D015398:Signal Transduction; D010738:Type C Phospholipases / Q000378:metabolism
D010982:Platelet-Derived Growth Factor; D011994:Recombinant Proteins; D004247:DNA; D017479:Receptors, Platelet-Derived Growth Factor; D010738:Type C Phospholipases; D020558:GTP Phosphohydrolases; D019204:GTP-Binding Proteins; D001839:Bombesin