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The Journal of Cell Biology, Vol 122, 95-101, Copyright © 1993 by The Rockefeller University Press
ARTICLES |
MW Bosenberg, A Pandiella and J Massague
Cell Biology and Genetics Program, Memorial Sloan-Kettering Cancer Center, New York 10021.
The ectodomain of proTGF-alpha, a membrane-anchored growth factor, is converted into soluble TGF-alpha by a regulated cellular proteolytic system that recognizes proTGF-alpha via the C-terminal valine of its cytoplasmic tail. In order to define the biochemical components involved in proTGF-alpha cleavage, we have used cells permeabilized with streptolysin O (SLO) that have been extensively washed to remove cytosol. PMA, acting through a Ca(2+)-independent protein kinase C, activates cleavage as efficiently in permeabilized cells as it does in intact cells. ProTGF-alpha cleavage is also stimulated by GTP gamma S through a mechanism whose pharmacological properties suggest the involvement of a heterotrimeric G protein acting upstream of the PMA- sensitive Ca(2+)-independent protein kinase C. Activated proTGF-alpha cleavage is dependent on ATP hydrolysis, appears not to require vesicular traffic, and acts specifically on proTGF-alpha that has reached the cell surface. These results indicate that proTGF-alpha is cleaved from the cell surface by a regulated system whose signaling, recognition, and proteolytic components are retained in cells devoid of cytosol.
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