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© The Rockefeller University Press, 0021-9525/1999//413 $5.00
The Journal of Cell Biology, Volume 144, Number 3, , 1999 413-425


Regular Articles

Evidence That Atypical Protein Kinase C-{lambda} and Atypical Protein Kinase C-{zeta} Participate in Ras-mediated Reorganization of the F-actin Cytoskeleton



Florian Überall*, Karina Hellbert*, Sonja Kampfer*, Karl Maly*, Andreas Villunger*, Martin Spitaler*, James Mwanjewe*, Gabriele Baier-Bitterlich*, Gottfried Baier{ddagger}, and Hans H. Grunicke*

* Institute of Medical Chemistry and Biochemistry and {ddagger} Institute of Medical Biology and Human Genetics, University of Innsbruck, A-6020 Innsbruck, Austria

Expression of transforming Ha-Ras L61 in NIH3T3 cells causes profound morphological alterations which include a disassembly of actin stress fibers. The Ras-induced dissolution of actin stress fibers is blocked by the specific PKC inhibitor GF109203X at concentrations which inhibit the activity of the atypical aPKC isotypes {lambda} and {zeta}, whereas lower concentrations of the inhibitor which block conventional and novel PKC isotypes are ineffective. Coexpression of transforming Ha-Ras L61 with kinase-defective, dominant-negative (DN) mutants of aPKC-{lambda} and aPKC-{zeta}, as well as antisense constructs encoding RNA-directed against isotype-specific 5' sequences of the corresponding mRNA, abrogates the Ha-Ras–induced reorganization of the actin cytoskeleton. Expression of a kinase-defective, DN mutant of cPKC-{alpha} was unable to counteract Ras with regard to the dissolution of actin stress fibers. Transfection of cells with constructs encoding constitutively active (CA) mutants of atypical aPKC-{lambda} and aPKC-{zeta} lead to a disassembly of stress fibers independent of oncogenic Ha-Ras. Coexpression of (DN) Rac-1 N17 and addition of the phosphatidylinositol 3'-kinase (PI3K) inhibitors wortmannin and LY294002 are in agreement with a tentative model suggesting that, in the signaling pathway from Ha-Ras to the cytoskeleton aPKC-{lambda} acts upstream of PI3K and Rac-1, whereas aPKC-{zeta} functions downstream of PI3K and Rac-1.

This model is supported by studies demonstrating that cotransfection with plasmids encoding L61Ras and either aPKC-{lambda} or aPKC-{zeta} results in a stimulation of the kinase activity of both enzymes. Furthermore, the Ras-mediated activation of PKC-{zeta} was abrogated by coexpression of DN Rac-1 N17.

Key Words: Ha-Ras L61 • atypical PKC • F-actin • Rac-1 • PI3K



Abbreviations used in this paper: a, atypical; c, conventional; CA, constitutively active; DN, dominant-negative; GFP, green fluorescence protein; n, novel; PI3K, phosphatidylinositol-3' kinase; PKC, protein kinase C; PVDF, polyvinylene difluoride.

F. Überall and K. Hellbert contributed equally to this work.



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