PKC Isoenzymes in the Chicken Lens and TPA-Induced Effects on Intercellular Communication

PURPOSE. Because lens connexins are phosphoproteins and intercellular communication between lens cells may be modulated by connexin phosphorylation, experiments were designed to characterize the expression of protein kinase C (PKC) isoenzymes in the chicken lens and in lentoid-containing cultures and to study the effects of 12-O-tetradecanoylphorbol-13-acetate (TPA) treatment on the distribution of PKC isoenzymes and intercellular communication. METHODS. The presence and distribution of PKC isoenzymes were studied by immunoblot analysis and immunofluorescence in chicken lens sections and in cell cultures under control conditions and after treatment with TPA. Intercellular communication was assessed by transfer of microinjected Lucifer yellow. RESULTS. PKC a, γ, ι, e, and μ were detected in lens homogenates by immunoblot analysis. The levels of PKC a, y, ι, and μ decreased between the 7th and the 18th embryonic days. Levels of PKC e remained relatively constant during the period of study. Similarly, lens cells in culture expressed isoenzymes a, y, e, ι, and μ. PKC β was not detected in lens or culture homogenates. In lens sections, all PKC isoenzymes analyzed were present in epithelial cells, in the annular pad region, and in the posterior aspect of fiber cells. The anti-PKC y antibody also stained fiber cell membranes. Analysis of lentoid cultures by immunofluorescence revealed that PKC γ, e, and ι and minimal amounts of PKC a were present in lentoid cells. Treatment with 200 nM TPA for 15 to 30 minutes induced translocation of PKC y to the plasma membrane of lentoid cells and significantly reduced the transfer of microinjected Lucifer yellow. CONCLUSIONS. Several PKC isoenzymes are expressed by lens cells in situ and in culture. The y isoenzyme, present in lens fibers, was activated in lentoid cells by TPA, a known activator of PKC. We have previously demonstrated TPA-induced phosphorylation of the gap junction protein connexin56 (Cx56). The new data presented in the current study demonstrate that TPA treatment also decreased intercellular communication. Taken together, the results suggest that differential phosphorylation of Cx56 by PKCy may induce a conformational change in the protein which, in turn, might lead to channel closure.