Endocytosis by digest cells of the cattle tick Boophilus microplus: regulation by protein kinase C

Endocytosis of fluorescently-labeled bovine serum albumin by digest cells of the gut of the cattle tick Boophilus microplus is inhibited by approx 60% in the presence of the tumour promoter 12-O-tetradecanoylphorbol 13-acetate. The results are consistent with a role for protein kinase C in regulating the uptake of blood meal by digest cells. Protein kinase C activity has been measured in the digest cell and the amount of enzyme has also been determined using a phorbol ester binding assay. The presence of a small number of specific protein kinase C substrates in the plasma membrane of the digest cell has been demonstrated. Preliminary experiments indicate that one of these substrates, a protein of approximately 30 kDa, is an integral membrane protein, part of which is exposed on the extracellular surface of the digest cell.