ACTIVATION OF A NOVEL CALCIUM-DEPENDENT PROTEIN-TYROSINE KINASE - CORRELATION WITH C-JUN N-TERMINAL KINASE BUT NOT MITOGEN-ACTIVATED PROTEIN-KINASE ACTIVATION

Many G protein-coupled receptors (e.g. that of angiotensin II) activat e phospholipase C beta, initially increasing intracellular calcium and activating protein kinase C. In the WB and GN4 rat liver epithelial c ell lines, agonist-induced calcium signals also stimulate tyrosine pho sphorylation and subsequently increase the activity of c-Jun N-termina l kinase (JNK), We have now purified the major calcium-dependent tyros ine kinase (CADTK), and by peptide and nucleic acid sequencing identif ied it as a rat homologue of human PYK2. CADTK/PYK2 is most closely re lated to p125(FAK) and both enzymes are expressed in WE and GN4 cells, Angiotensin II, which only slightly increases p125(FAK) tyrosine phos phorylation in GN4 cells, substantially increased CADTK tyrosine autop hosphorylation and kinase activity, Agonists for other G protein-coupl ed receptors (e.g. LPA), or those increasing intracellular calcium (th apsigargin), also stimulated CADTK. In comparing the two rat liver cel l lines, GN4 cells exhibited similar to 5-fold greater angiotensin II- and thapsigargin-dependent CADTK activation than WB cells, Although m aximal JNK activation by stress-dependent pathways (e.g. UV and anisom ycin) was equivalent in the two cell lines, calcium-dependent JNK acti vation was B-fold greater in GN4, correlating with CADTK activation. I n contrast to JNK, the thapsigargin-dependent calcium signal did not a ctivate mitogen-activated protein kinase and Ang II-dependent mitogen- activated protein kinase activation was not correlated with CADTK acti vation. Finally, while some stress-dependent activators of the JNK pat hway (NaCl and sorbitol) stimulated CADTK, others (anisomycin, UV, and TNF alpha) did not, In summary, cells expressing CADTK/PYK2 appear to have two alternative JNK activation pathways: one stress-activated an d the other calcium-dependent.