In Spodoptera frugiperda (Sf9) insect cells infected with a recombinant baculovirus carrying a gene construct encoding human CD4 endocytosis of CD4 is induced after stimulation with phorbol-12-myristate-13-acetate (PMA). Stimulation of endocytosis with PMA reduced the amount of full-length CD4 on the plasma membrane of Sf9 cells by 50% after 2 hours. Endocytosis of CD4 is blocked after intracellular delivery by cationic liposomes of a monoclonal antibody directed against a cytoplasmic sequence of CD4. Endocytosis is also blocked by the calmodulin inhibitor W7. The PKC inhibitor H7 does not inhibit PMA-induced endocytosis. A truncated CD4, in which the last 32 C-terminal amino acids were deleted did, not respond to PMA. Our results show that PMA can stimulate the calmodulin-dependent signal transduction for endocytosis of full-length CD4 in Sf9 cells. Phosphorylation of CD4 in Sf9 cells was not detectable after PMA treatment and PKC is not required for endocytosis.

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http://dx.doi.org/10.1006/bbrc.1995.1203DOI Listing

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