EPIDERMAL GROWTH-FACTOR STIMULATES TYROSINE PHOSPHORYLATION OF PHOSPHOLIPASE C-II INDEPENDENTLY OF RECEPTOR INTERNALIZATION AND EXTRACELLULAR CALCIUM
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- EPIDERMAL GROWTH-FACTOR STIMULATES TYROSINE PHOSPHORYLATION OF PHOSPHOLIPASE C-II INDEPENDENTLY OF RECEPTOR INTERNALIZATION AND EXTRACELLULAR CALCIUM
- Wahl, Matthew I.; Nishibe, Shunzo; Suh, Pann-Ghill; Rhee, Sue Goo; Carpenter, Graham
- Issue Date
- NATL ACAD SCIENCES
- PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, v.86, no.5, pp.1568 - 1572
- Epidermal growth factor (EGF) rapidly stimulates the formation of inositol 1,4,5-trisphosphate in a variety of cell types. Previously we have found that in intact cells stimulation of phospholipase C (PLC) activity by EGF is correlated with the retention of increased amounts of PLC activity by a phosphotyrosine immunoaffinity matrix, suggesting that the EGF-receptor tyrosine kinase phosphorylates PLC. We now define parameters of the mechanism by which EGF addition to A-431 cells stimulates phosphotyrosine immuno-isolation of PLC activity and demonstrate that EGF addition to A-431 cells increases tyrosine phosphorylation of PLC. EGF rapidly and reversibly stimulated the anti-phosphotyrosine recovery of increased PLC activity when cells were treated with growth factor at 3°C, indicating that receptor internalization is not required and that the phosphorylation event occurs prior to formation of inositol 1,4,5-trisphosphate. Also, the EGF stimulation of anti-phosphotyrosine recovery of PLC activity occurred in the absence of extracellular Ca2+. Stimulation of PLC activity in intact cells by other agonists, such as bradykinin or ATP, did not result in increased anti-phosphotyrosine recovery of PLC activity, suggesting two separate mechanisms exist in A-431 cells for hormone-stimulated formation of inositol phosphates. Finally, using monoclonal antibodies that specifically recognize three distinct PLC isozymes, we show that an ≃145-kDa PLC isozyme (PLC-II) is present in A-431 cells and that EGF treatment of A-431 cells stimulates phosphorylation of PLC-II on both tyrosine and serine residues.
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