Parallel changes in amino acid transport and protein kinase C localization in LLC‐PK1 cells treated with TPA or diradylglycerols

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Abstract
Protein kinase C is considered to be a major target for tumor promoting phorbol esters such as 12‐O‐tetradecanoylphorbol‐13‐acetate (TPA). We have analyzed the correlation between A‐system amino acid transport and the distribution of protein kinase C (PKC) between a membrane‐rich fraction (100,000 g pellet) and cytosol (supernatant) from homogenized LLC‐PK1 cells, a pig kidney epithelial cell line grown in culture. During log growth 1 day after seeding the cells onto culture plates, PKC activity is high in the membrane fraction and low in the cytosol. As the cells become confluent the PKC distribution shifts to a cytosolic pool. Concomitantly, A‐system amino acid transport, as measured by methylaminoisobutyric acid [14C]MeAIB uptake, decreases. TPA (0.01–1.0 μM) induces a shift of PKC activity from the cytosol back to the membrane‐rich fraction in post‐confluent cells with a concomitant 2–3 fold stimulation of MeAIB uptake. The same responses can be achieved by treating cells with certain diradylglycerols, either diacylglycerols such as 1‐oleyl‐2‐acetyl‐sn‐glycerol (OAG) or alkylacylglycerols such as 1‐hexadecenyl‐2‐oleyl‐sn‐glycerol. Both responses to TPA are blocked by cytochalasin B, but cycloheximide inhibits the transport response without affecting PKC redistribution. It is suggested that the redistribution may be a necessary but not sufficient concomitant to the transport activation.