Evidence for the involvement of two pathways in activation of extracellular signal-regulated kinase (Erk) and cell proliferation by Gi and Gq protein-coupled receptors in osteoblast-like cells
J. Caverzasio et al., Evidence for the involvement of two pathways in activation of extracellular signal-regulated kinase (Erk) and cell proliferation by Gi and Gq protein-coupled receptors in osteoblast-like cells, J BONE MIN, 15(9), 2000, pp. 1697-1706
The mechanisms by which Gi and Gq protein-coupled receptors mediate mitogen
ic signaling in osteoblast-like cells are unknown and were investigated in
MC3T3-E1 cells using specific receptor agonists such as lysophosphatidic ac
id (LPA) and prostaglandin F-2 alpha (PGF(2 alpha)). In contrast to their i
mplication in epidermal growth factor (EGF) receptor tyrosine kinase signal
ing, the adaptor protein Shc, the Grb2/Sos complex, and the small G protein
Ras were not involved in the activation of Erk induced by either LPA or PG
F(2 alpha) in MC3T3-E1 cells, suggesting that activation of Erk by Gi and G
q protein-coupled receptors is Ras independent in these cells, Using specif
ic kinase inhibitors and kinetic analyses, we provide evidence for two dist
inct components in the activation of Erk by Gi and Gq protein-coupled recep
tors in MC3T3-E1 cells including an Src-like kinase-dependent pathway and a
protein kinase C (PKC)-dependent mechanism. Functional analyses suggested
that these two components are required for optimal DNA synthesis in respons
e to LPA and PGF(2 alpha). These results suggest the implication of two pat
hways in the stimulation of Erk and cell replication by growth factors acti
ng through Gi and Gq protein-coupled receptors in bone-forming cells.