Gonadotropin release and redistribution of calcium-activated, phospholipid-dependent protein kinase in phorbol-stimulated rat pituitary cells |
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Authors: | K Hirota T Hirota G Aguilera K J Catt |
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Affiliation: | 1. DST/CSIR National Centre for Nanostructured Materials, Council for Scientific and Industrial Research, Pretoria 0001, South Africa;2. Department of Chemical, Metallurgical and Materials Engineering, Tshwane University of Technology, Pretoria 0001, South Africa;3. Department of Applied Chemistry, University of Johannesburg, Doornfontein 2028, Johannesburg, South Africa;4. Department of Environmental, Water and Earth Sciences, Tshwane University of Technology, Pretoria 0001, South Africa |
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Abstract: | The effect of phorbol esters on calcium-activated, phospholipid-dependent kinase (protein kinase C) and luteinizing hormone (LH) secretion was examined in cultured rat anterior pituitary cells. The potent tumor promoter 12-O-tetra-decanoylphorbol-13-acetate (TPA) stimulated LH secretion and activated pituitary protein kinase C in the presence of calcium and phosphatidylserine. The enzyme activity present in cytosol and particulate fractions was eluted at about 0.05 M NaCl during DE52-cellulose chromatography. Preincubation of pituitary cells with TPA markedly decreased cytosolic protein kinase C activity and increased enzyme activity in the particulate fraction. The maximal TPA-induced change in enzyme activity, with a 76% decrease in cytosol and a 4.3-fold increase in the particulate fraction, occurred within 10 min. The dose-dependent changes in protein kinase C redistribution in TPA-treated cells were correlated with the stimulation of LH release by the phorbol ester. These results suggest that activation of protein kinase C by TPA is associated with intracellular redistribution of the enzyme and is related to the process of secretory granule release from gonadotrophs. |
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