Up-regulation of Phosphatidylinositol-3 Kinase Signaling in plcg1 Gene Null Fibroblasts.
Phospholipase C-gamma1(PLC-gamma1) and phosphatidylinositol-3 kinase(PI-3K) play crucial role in growth factor-induced cell growth and proliferation. To investigate the complementary mechanism of PLC-gamma1 in cell growth and epidermal growth factor (EGF)-induced mitogenic signaling, PLC-gamma1 deficient mouse embryonic fibroblasts(PLC-gamma1(-/-)) and its wild type(PLC-gamma1(+/+)) were exposed to U73122, a phospholipase C-specific inhibitor, or wortmannin, a PI-3K inhibitor then the clonogenicity, viability, EGF-induced DNA synthesis of the two cell lines were determined by cloning formation, MTT method and (3)H -thymidine incorporation assay. Results showed that either U73122 or wortmannin inhibited PLC-gamma1(-/-) and PLC-gamma1(+/+) cells in terms of EGF-induced DNA synthesis, cloning formation and cell viability, but PLC-gamma1(-/-) cells were more dependent on PI-3K and less dependent on PLC compared with wild types. The PLC-gamma1 signaling pathway of PLC-gamma1(-/-) cells might be complemented by PI-3K pathway, because after EGF stimulation, the tyrosine phospholation of p85alpha PI-3K increased significantly in PLC-gamma1(-/-), but not in PLC-gamma2(-/-), as Western blotting showed that there was neither complementary PLC-gamma2 expression in PLC-gamma1(-/-) cells, nor other PLC isozymes such as PLC-beta and PLC-delta. These results suggest the redundancy of EGF-mediated signaling and the complementary mechanism of PLC-gamma1 pathway.
Bai
X C
XC
Department of Cell Biology and Medical Genetics, the First Military Medical University, Guangzhou 510515, China. baixc15@263.net
Luo
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SQ
Bai
J
J
Deng
F
F
Zheng
W S
WS
Ji
Q S
QS