Protein kinase D is sufficient to suppress EGF-induced c-Jun Ser 63 phosphorylation

Phosphorylation of c-Jun at Ser 63/73 by the c-Jun N-terminal kinase (JNK) potentiates the transactivation function of c-Jun. Protein kinase D (PKD), a downstream effector of protein kinase C (PKC) has been implicated in the attenuation of epidermal growth factor (EGF)-induced activation of JNK. In order to determine whether activated PKD is sufficient to modulate the EGF- JNK-c-Jun pathway, we have developed a cellular model system, utilizing hum an embryonic kidney cells (HEK 293), in which stably transfected, constitut ively active or kinase dead mutants of PKD can be inducibly expressed by th e insect hormone, ecdysone. Induced expression of constitutively active, bu t not kinase dead PKD, suppressed EGF stimulated c-Jun phosphorylation at S er 63, demonstrating that activated PKD is sufficient to suppress c-Jun pho sphorylation. This is the first demonstration that PKD modulates phosphoryl ation of the protooncogene c-Jun at a site critical for its ability to medi ate cell proliferation and differentiation. (C) 2001 Academic Press.