We have examined the distribution of phospholipase C-γ1 (PLC-γ1) between membrane and cytosolic fractions in several cell lines. In MDA-468 cells, which are derived from a human breast tumor, greater than one-half of the total PLC-γ1 is associated with the membrane fraction of the cell. Unlike the situation in A-431 cells [G. Todderud, M. I. Wahl, S. G. Ree, and G. Carpenter, Science, 248: 296–298, 1990], epidermal growth factor (EGF) stimulation of MDA-468 cells does not result in significantly increased PLC-γ1 association with membranes. Immunoblot analysis reveals low levels of phosphotyrosine in PLC-γ1 and EGF receptors in unstimulated MDA-468 cells and greatly increased phosphotyrosine levels in these proteins as a result of EGF stimulation of the cells. We conclude that autocrine activation of EGF receptors is not responsible for the elevated association of PLC-γ1 with membranes in these cells.

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This work was supported by NIH Grants CA43720 and AM07491.

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©1992 American Association for Cancer Research.
1992
American Association for Cancer Research, Inc.