Identification of an oncoprotein- and UV-responsive protein kinase that binds and potentiates the c-Jun activation domain.

  1. M Hibi,
  2. A Lin,
  3. T Smeal,
  4. A Minden, and
  5. M Karin
  1. Department of Pharmacology, University of California San Diego, School of Medicine, La Jolla 92093-0636.

Abstract

The activity of c-Jun is regulated by phosphorylation. Various stimuli including transforming oncogenes and UV light, induce phosphorylation of serines 63 and 73 in the amino-terminal activation domain of c-Jun and thereby potentiate its trans-activation function. We identified a serine/threonine kinase whose activity is stimulated by the same signals that stimulate the amino-terminal phosphorylation of c-Jun. This novel c-Jun amino-terminal kinase (JNK), whose major form is 46 kD, binds to a specific region within the c-Jun trans-activation domain and phosphorylates serines 63 and 73. Phosphorylation results in dissociation of the c-Jun-JNK complex. Mutations that disrupt the kinase-binding site attenuate the response of c-Jun to Ha-Ras and UV. Therefore the binding of JNK to c-Jun is of regulatory importance and suggests a mechanism through which protein kinase cascades can specifically modulate the activity of distinct nuclear targets.

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