Transactivation of the Epidermal Growth Factor Receptor Mediates Parathyroid Hormone and Prostaglandin F2α-Stimulated Mitogen-Activated Protein Kinase Activation in Cultured Transgenic Murine Osteoblasts

• Published in: Molecular endocrinology (Baltimore, Md.) Md.), 2003-08, Vol.17 (8), p.1607-1621
• Main Authors: Ahmed, Intekhab, Gesty-Palmer, Diane, Drezner, Marc K, Luttrell, Louis M
• Format: Article
• Language: English
• Subjects: Animals; Cell Differentiation - drug effects; Cells, Cultured; Cyclic AMP-Dependent Protein Kinases - drug effects; Cyclic AMP-Dependent Protein Kinases - metabolism; Dinoprost - pharmacology; Enzyme Activation; Epidermal Growth Factor - metabolism; Epidermal Growth Factor - pharmacology; Lysophospholipids - pharmacology; Mice; Mice, Transgenic; Mitogen-Activated Protein Kinase 1 - drug effects; Mitogen-Activated Protein Kinase 1 - metabolism; Mitogen-Activated Protein Kinase 3; Mitogen-Activated Protein Kinases - drug effects; Mitogen-Activated Protein Kinases - metabolism; Osteoblasts - drug effects; Osteoblasts - metabolism; Parathyroid Hormone - metabolism; Parathyroid Hormone - pharmacology; Phosphorylation; Protein Kinase C - drug effects; Protein Kinase C - metabolism; Quinazolines; Rats; Receptor, Epidermal Growth Factor - antagonists & inhibitors; Receptor, Epidermal Growth Factor - drug effects; Receptor, Epidermal Growth Factor - metabolism; Receptors, G-Protein-Coupled - drug effects; Receptors, G-Protein-Coupled - metabolism; Receptors, Lysophosphatidic Acid; Receptors, Prostaglandin - drug effects; Receptors, Prostaglandin - metabolism; Signal Transduction; Transcriptional Activation; Tyrphostins - pharmacology
• ISSN: 0888-8809; 1944-9917
• DOI: 10.1210/me.2002-0040

Recent data suggest that G protein-coupled receptors (GPCRs), including those for PTH and prostaglandins (PGs), contribute to the proliferation and differentiation of osteoblasts in vivo. To understand how these signals are transduced, we studied activation of the ERK1/2 MAPK cascade in cultures of differentiating TMOb murine osteoblasts. In TMOb cells, stimulation of endogenous Gs/Gq-coupled PTH receptors, Gq-coupled PGF2α receptors, and Gi/Gq-coupled lysophosphatidic acid receptors, but not Gs-coupled PGE2 receptors, caused a rapid 5- to 10-fold increase in ERK1/2 phosphorylation. GPCR-stimulated ERK1/2 activation coincided with increased tyrosine phosphorylation of epidermal growth factor (EGF) receptors and was blocked by the EGF receptor inhibitor, tyrphostin AG1478, and the metalloprotease inhibitor, batimastat, suggesting that the response involved transactivation of EGF receptors through the proteolytic release of an EGF receptor ligand. To further examine the mechanism of PTH-stimulated EGF receptor transactivation, we employed COS-7 cells expressing the rat PTH receptor. Here, stimulation with PTH(1–34) caused proteolysis of hemagglutinin epitope-tagged heparin binding-EGF, increased tyrosine autophosphorylation of EGF receptors, and AG1478-sensitive ERK1/2 activation. When PTH receptor-expressing COS-7 cells were placed in a mixed culture with cells lacking the PTH receptor but expressing a green fluorescent protein-tagged ERK2, stimulation with PTH(1–34) induced phosphorylation of green fluorescent protein-ERK2 that was abolished by either batimastat or tyrphostin AG1478. These data suggest that autocrine/paracrine cross-talk between EGF receptors and Gi- or Gq/11-coupled GPCRs represents the predominant mechanism of GPCR-mediated activation of ERK1/2 in cultured TMOb osteoblasts.