P38-mitogen activated protein kinases (of which there are 4 isoforms; α, β, γ and δ) are serine/threonine kinases that are activated in response to stress stimuli. Classically studies have only examined the role of p38α in the myocardium. However, p38γ is also highly and preferentially expressed in the myocardium. The aim of this study is to investigate the role of p38γ in the progression of pathological hypertrophy following abdominal aortic banding. Comparisons of cardiac function and structure of wild type (WT) and p38γ knock out (KO) mice in response to abdominal aortic banding found that KO mice develop less ventricular hypertrophy than their corresponding WT controls, and have preserved cardiac function. We observed that basal p38γ myocardial staining is primarily localised at the membranes and throughout the cytoplasm. Following aortic constriction nuclear staining of p38γ incre ases but no accumulation of p38α is observed. This suggests that the two isoforms play distinct roles in the heart.
To elucidate its signaling pathway and identify endogenous substrates of p38γ we have generated an analogue sensitive p38γ, which is mutated at a gatekeeper residue, to specifically track endogenous substrates in the myocardium. The mutation allows only the mutant kinase, but not WT kinases, to utilise analogues of ATP that are expanded at the N-6 position and contain a visible tag on the γ-phosphate. Transfer of this tag to substrates allows subsequent isolation and identification. Using this technique we have been able to identify, amongst other substrates, Cypher and Calpastatin as novel targets of p38γ.
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