title: Role of intracellular calcium and protein kinase C in the endocytosis of transferrin and insulin by HL60 cells.
abstract: The role of the cytosolic free calcium concentration ([Ca2+]i) and of protein kinase C on the internalization of transferrin and insulin in the human promyelocytic cell line HL60 was investigated. [Ca2+]i was selectively monitored and manipulated by the use of the fluorescent Ca2+ indicator and buffer quin2, while receptor-ligand internalization was studied directly by quantitative electron microscope autoradiography. Decreasing the [Ca2+]i up to 10-fold below resting level had no effect on the internalization of transferrin or insulin. Similarly, a 10-fold elevation of the [Ca2+]i using the calcium ionophore ionomycin caused little or no change in the endocytosis of the two ligands. In contrast, activation of protein kinase C by phorbol myristate acetate markedly stimulated the internalization of both occupied and unoccupied transferrin receptors, even in cells with very low [Ca2+]i. The insulin receptor was found to behave differently in response to phorbol myristate acetate, however, in that only the occupied receptors were stimulated to internalize. We conclude that the [Ca2+]i plays only a minor role in regulating receptor-mediated endocytosis, whereas protein kinase C can selectively modulate receptor internalization depending on receptor type and occupancy.
mesh_terms: D002118:Calcium / Q000502:physiology*; D002460:Cell Line; D004705:Endocytosis; D006801:Humans; D007328:Insulin / Q000378:metabolism*; D015470:Leukemia, Myeloid, Acute; D011493:Protein Kinase C / Q000502:physiology*; D011972:Receptor, Insulin / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000378:metabolism; D011990:Receptors, Transferrin; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014168:Transferrin / Q000378:metabolism*
chemical_list: D007328:Insulin; D011956:Receptors, Cell Surface; D011990:Receptors, Transferrin; D014168:Transferrin; D011972:Receptor, Insulin; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium