Activation of p38 mitogen-activated protein kinase by PYK2/related adhesion focal tyrosine kinase-dependent mechanism

The stress-activated p38 mitogen-activated protein kinase (p38 MAPK), a mem ber of the subgroup of mammalian kinases, appears to play an important role in regulating inflammatory responses, including cytokine secretion and apo ptosis, The upstream mediators that link extracellular signals with the p38 MAPK signaling pathway are currently unknown. Here we demonstrate that pp1 25 focal adhesion kinase-related tyrosine kinase RAFTK (also known as PYK2, CADTK) is activated specifically by methylmethane sulfonate (MMS) and hype rosmolarity but not by ultraviolet radiation, ionizing radiation, or cis-pl atinum. Overexpression of RAFTK leads to the activation of p38 MAPK, Furthe rmore, overexpression of a dominant-negative mutant of RAFTK (RAFTK K-M) in hibits MMS-induced p38 MAPK activation. MKK3 and MKK6 are known potential c onstituents of p38 MAPK signaling pathway, whereas SEK1 and MEK1 are upstre am activators of SAPK/JNK and ERK pathways, respectively. We observe that t he dominant-negative mutant of MKK3 but not of MKK6, SEK1, or MEK1 inhibits RAFTK-induced p38 MAPK activity. Furthermore, the results demonstrate that treatment of cells with 1,2-bis(2-aminophenoxy)ethane-N,N,N'.N'-tetraaceti c acid, tetra(acetoxymethyl)-ester, a membrane-permeable calcium chelator, inhibits MMS-induced activation of RAFTK and p38 MAPK. Taken together, thes e findings indicate that RAFTK represents a stress-sensitive mediator of th e p38 MAPK signaling pathway in response to certain cytotoxic agents.