We attempted to determine whether or not activation of calcium phospholipid-dependent protein kinase C (PKC) is associated with the induction of differentiation by 12-O-tetradecanoylphorbol-13-acetate (TPA) in the human T-lymphoblastic cell line MOLT-3. PKC activities were assayed in MOLT-3 and its five subclones resistant to TPA-induced cell differentiation. The cytosolic PKC activities of TPA-resistant subclones were 36-53% of that of the parental MOLT-3 cells. TPA treatment led to a rapid decrease in PKC activities in the cytosol, together with a concomitant increase in PKC activities in the particulate fraction, in both MOLT-3 and a TPA-resistant subclone. Thus, translocation of PKC from the cytosol to the membrane occurred following treatment with TPA, in both cell lines. However, the amount of PKC translocated from the cytosol to particulate fraction for 60min in a TPA-resistant subclone was about 20% of that of the parental MOLT-3 cells. These findings suggest that the quantity of cytosolic PKC activity and the extent of translocation may relate to responses to TPA-induced cell differentiation in this T-cell line.
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