Protein kinase C associates with intermediate filaments and stress fibers

The subcellular distribution of protein kinase C (PKC) was determined by immunofluorescence using anti-PKC monoclonal antibodies (MAbs). The antibodies used were: (1) 1.9 MAb that is directed against an epitope in the catalytic domain of PKC, (2) 1.3 MAb that recognizes an isozyme of PKC (Mochly-Rosen D. and Koshland D.E., 1987, J. Biol. Chem. 262, 2291–2297; Mochly-Rosen D., et al. 1987 Proc. Natl. Acad. Sci. USA 84, 4660–4664) and (3) MC-2a MAb that is directed against the β-isozyme of PKC (Usuda N., et al. 1991, J. Cell Biol. 112, 1241–1247). The cells used in this study were baby hamster kidney cells, vimentin+ and vimentin− clones of SW13 (a human adrenal carcinoma cell line), CEM (a human T cell line), U937 (a histiocytic myeloid cell line), and HL60 (a promyelocytic leukemia cell line). The 1.9 MAb was found to recognize a variety of subcellular components, viz., nucleus (nucleoplasm and nucleolus), cytoplasm, vimentin-type intermediate filaments (IF), stress fibers, and cell membrane. Among these components the β-isozyme-specific MAbs (1.3 and MC-2a) recognized only the IF network, stress fibers, and edges of the cell membrane. Experiments with vimentin+ and vimentin mutants of SW13 cells, double indirect immunofluorescence studies with anti-vimentin and anti-PKC antibodies, and drug studies confirmed that the IF network is the predominant cytoskeletal network labeled with all anti-PKC MAbs. Immunoblotting studies with the MC-2a MAb revealed that the observed staining of the IF network was not due to a cross-reaction of the MAb with IF proteins and that the MAb specifically recognizes PKC. These studies, while identifying the diverse cell components to which PKC binds, have demonstrated, for the first time, that PKC associates with the IF network in a variety of cell types. Additionally, the studies have confirmed the studies by others concerning the association of PKC with Stress fibers.