¹Institute of Toxicology, Johannes Gutenberg-University of Mainz, 55131 Mainz, Germany

²Institute of Physiological Chemistry, Johannes Gutenberg-University of Mainz, 55131 Mainz, Germany

Correspondence to: C Dietrich, Institute of Toxicology, Johannes Gutenberg-University of Mainz, Obere Zahlbacher Str. 67, 55131 Mainz, Germany. E-mail: cdietric@mail.uni-mainz.de

^aCurrent address: Byk Gulden, 78467 Konstanz, Germany.

^bCurrent address: innoTides GmbH, its, 52499 Baesweiler, Germany.

^cCurrent address: Axxima Pharmaceuticals AG, 82152 Martinsried, Germany

There is evidence that protein kinase C (PKC) is a tumor suppressor, although its physiological role has not been elucidated so far. Since important anti-proliferative signals are mediated by cell-cell contacts we studied whether PKC is involved in contact-dependent inhibition of growth in human (FH109) and murine (NIH3T3) fibroblasts. Cell-cell contacts were imitated by the addition of glutardialdehyde-fixed cells to sparsely seeded fibroblasts. Downregulation of the PKC isoforms , , , and after prolonged treatment with 12-O-tetradecanoylphorbol-13-acetate (TPA, 0.1 M) resulted in a significant release from contact-inhibition in FH109 cells. Bryostatin 1 selectively prevented TPA-induced PKC-downregulation and reversed TPA-induced release from contact-inhibition arguing for a role of PKC in contact-inhibition. In accordance, the PKC specific inhibitor Rottlerin (1 M) totally abolished contact-inhibition. Interestingly, immunofluorescence revealed a rapid translocation of PKC to the nucleus when cultures reached confluence with a peak in early-mid G1 phase. Nuclear translocation of PKC in response to cell-cell contacts could also be demonstrated after subcellular fractionation by Western blotting and by measuring PKC-activity after immunoprecipitation. Transient transfection of NIH3T3 cells with a dominant negative mutant of PKC induced a transformed phenotype. We conclude that PKC is involved in contact-dependent inhibition of growth. Oncogene (2001) 20, 5143-5154.

contact-inhibition; PKC; fibroblast