Abstract 336: TAB1 Initiates p38α Autophosphorylation During Myocardial Ischemia

Abstract

The p38 mitogen-activated protein kinase (MAPK) family has been implicated in many aspects of cell biology including inflammation, gene expression, cell cycle progression, differentiation and apoptosis. The canonical pathway of p38 activation results in dual phosphorylation of p38 induced via TGF-beta activated kinase 1 (TAK1) which is an upstream Ser/Thr kinase of the MAPK kinases (MKK) of p38; MKK3/6. However, a MKK-independent mechanism of activation is proposed as TAK 1 binding protein 1 (TAB1) appears to induce autophosphorylation of p38 through a direct interaction during myocardial ischaemia, worsening injury. When human embryonic kidney cells are transfected with wild-type TAB1, there is a marked increase in activating dual phosphorylation of p38 compared to untransfected cells (5.3 ± 1.9 normalised to untransfected). The ATP-competitive p38 inhibitor SB203580 (1µM) markedly reduced the phosphorylation of transfected p38 (20.4 ± 9.7 vs 5.4 ± 1.5). An SB203580-resistant form of p38 (T106M) was also co-transfected with TAB1, and the resulting p38 phosphorylation was no longer reduced by the presence of SB203580 (12.4 ± 7.5 vs 12.0 ± 6.7) but was reduced by another pharmacological inhibitor, BIRB796 (10µM) that does not depend on T106 for binding (5.6 ± 1.1 vs 1.6 ± 0.4, P<0.05). In conclusion, these findings suggest that p38 activation by autophosphorylation is TAB1-mediated.