J Biol Chem, Vol. 273, Issue 42, 27654-27661, October 16, 1998

Differential Downstream Functions of Protein Kinase C and - in EL4 Mouse Thymoma Cells

Moira S. Resnick, Beom-Sik Kang^¶, Dien Luu^¶, Jeffery T. Wickham^¶, Julianne J. Sando, and Chang S. Hahn^¶

From the Department of  Pharmacology, ^¶ Microbiology, and Beirne B. Carter Center for Immunology Research, University of Virginia Health Sciences Center, Charlottesville, Virginia 22908

Sensitive EL4 mouse thymoma cells (s-EL4) respond to phorbol esters with growth inhibition, adherence to substrate, and production of cytokines including interleukin 2. Since these cells express several of the phorbol ester-sensitive protein kinase C (PKC) isozymes, the function of each isozyme remains unclear. Previous studies demonstrated that s-EL4 cells expressed substantially more PKC and PKC than did EL4 cells resistant to phorbol esters (r-EL4). To examine potential roles for PKC and PKC in EL4 cells, wild type and constitutively active versions of the isozymes were transiently expressed using a Sindbis virus system. Expression of constitutively active PKC, but not PKC, in s- and r-EL4 cells altered cell morphology and cytoskeletal structure in a manner similar to that of phorbol ester treatment, suggesting a role for PKC in cytoskeletal organization. Prolonged treatment of s-EL4 cells with phorbol esters results in inhibition of cell cycling along with a decreased expression of most of the PKC isozymes, including PKC. Introduction of virally expressed PKC, but not PKC, overcame the inhibitory effects of the prolonged phorbol ester treatment on cell cycle progression, suggesting a possible involvement of PKC in cell cycle regulation. These results support differential functions for PKC and PKC in T cell activation.