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Molecular and Cellular Biology, February 1999, p. 1313-1324, Vol. 19, No. 2
0270-7306/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Novel Roles of Specific Isoforms of Protein Kinase C in Activation of the c-fos Serum Response Element

Jae-Won Soh,1,2 Eun Hae Lee,2 Ron Prywes,3 and I. Bernard Weinstein3,*

Department of Biochemistry & Molecular Biophysics1 and Herbert Irving Comprehensive Cancer Center,2 College of Physicians & Surgeons, Columbia University, New York, New York 10032, and Department of Biological Sciences, Columbia University, New York, New York 100273

Received 8 May 1998/Returned for modification 1 July 1998/Accepted 3 November 1998

Protein kinase C (PKC) is a multigene family of enzymes consisting of at least 11 isoforms. It has been implicated in the induction of c-fos and other immediate response genes by various mitogens. The serum response element (SRE) in the c-fos promoter is necessary and sufficient for induction of transcription of c-fos by serum, growth factors, and the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA). It forms a complex with the ternary complex factor (TCF) and with a dimer of the serum response factor (SRF). TCF is the target of several signal transduction pathways and SRF is the target of the rhoA pathway. In this study we generated dominant-negative and constitutively active mutants of PKC-alpha , PKC-delta , PKC-varepsilon , and PKC-zeta to determine the roles of individual isoforms of PKC in activation of the SRE. Transient-transfection assays with NIH 3T3 cells, using an SRE-driven luciferase reporter plasmid, indicated that PKC-alpha and PKC-varepsilon , but not PKC-delta or PKC-zeta , mediate SRE activation. TPA-induced activation of the SRE was partially inhibited by dominant negative c-Raf, ERK1, or ERK2, and constitutively active mutants of PKC-alpha and PKC-varepsilon activated the transactivation domain of Elk-1. TPA-induced activation of the SRE was also partially inhibited by a dominant-negative MEKK1. Furthermore, TPA treatment of serum-starved NIH 3T3 cells led to phosphorylation of SEK1, and constitutively active mutants of PKC-alpha and PKC-varepsilon activated the transactivation domain of c-Jun, a major substrate of JNK. Constitutively active mutants of PKC-alpha and PKC-varepsilon could also induce a mutant c-fos promoter which lacks the TCF binding site, and they also induce transactivation activity of the SRF. Furthermore, rhoA-mediated SRE activation was blocked by dominant negative mutants of PKC-alpha or PKC-varepsilon . Taken together, these findings indicate that PKC-alpha and PKC-varepsilon can enhance the activities of at least three signaling pathways that converge on the SRE: c-Raf-MEK1-ERK-TCF, MEKK1-SEK1-JNK-TCF, and rhoA-SRF. Thus, specific isoforms of PKC may play a role in integrating networks of signal transduction pathways that control gene expression.

* Corresponding author. Mailing address: Herbert Irving Comprehensive Cancer Center, HHSC-1509, 701 West, 168th St., New York, NY 10032. Phone: (212) 305-6924. Fax: (212) 305-6889. E-mail: weinstein{at}cuccfa.ccc.columbia.edu.

Molecular and Cellular Biology, February 1999, p. 1313-1324, Vol. 19, No. 2
0270-7306/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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