The Essential Role of MEKK3 Signaling in Angiotensin II-induced Calcineurin/Nuclear Factor of Activated T-cells Activation

Shahrzad Abbasi,Bing Su,Rodney E Kellems,Jianhua Yang,Yang Xia

doi:10.1074/jbc.m506493200

Abstract

Calcineurin is a serine/threonine protein phosphatase that plays a critical role in many physiologic processes, such as T-cell activation, apoptosis, skeletal myocyte differentiation, and cardiac hypertrophy. We determined that active MEKK3 was capable of activating calcineurin/nuclear factor of activated T-cells (NFAT) signaling in cardiac myocytes and reprogramming cardiac gene expression. In contrast, small interference RNA directed against MEKK3 and a dominant negative form of MEKK3 caused the reduction of NFAT activation in response to angiotensin II in cardiac myocytes. Genetic studies showed that MEKK3-deficient mouse embryo fibroblasts failed to activate calcineurin/NFAT in response to angiotensin II, a potent NFAT activator. Conversely, restoring MEKK3 to the MEKK3-deficient cells restored angiotensin II-mediated calcineurin/NFAT activation. We determined that angiotensin II induced MEKK3 phosphorylation. Thus, MEKK3 functions downstream of the AT1 receptor and is essential for calcineurin/NFAT activation. Finally, we determined that MEKK3-mediated activation of calcineurin/NFAT signaling was associated with the phosphorylation of modulatory calcineurin-interacting protein 1 at Ser(108) and Ser(112). Taken together, our studies reveal a previously unrecognized novel essential regulatory role of MEKK3 signaling in calcineurin/NFAT activation.

Highlights

We showed that FK506, a calcineurin inhibitor, completely inhibited nuclear factor of activated T-cells (NFAT) activation by MEKK3(CA), indicating that calcineurin is involved in MEKK3-mediated NFAT activation (Fig. 1A)
We have presented multiple lines of evidence that MEKK3 is absolutely required for calcineurin/NFAT activation in response to angiotensin II (Ang II), a potent calcineurin/NFAT activator
Ang II-induced NFAT activation was restored to MEKK3-deficient mouse embryo fibroblasts following the introduction of an MEKK3 expression plasmid

Summary

Introduction

Inhibition of calcineurin activity with cyclosporin A or FK506 blocks cardiac hypertrophy in response to pressure overload, ␤-adrenergic stimulation, and sarcomere dysfunction [20, 21]. Peptides derived from the SP repeat domain of human MCIP1 inhibit calcineurin activity [27, 28] These findings support a competitive antagonist function for MCIP1 with respect to calcineurin action on NFAT proteins. Cardiac overexpression of MCIP1 in transgenic mice diminished hypertrophy in response to overexpression of a constitutively active form of calcineurin, as well as to chronic isoproterenol administration, pressure overload, and exercise [27, 33]. More recent evidence indicates that phosphorylation of RCN1, a yeast ortholog of MCIP1, enhances calcineurin activity [36], the mechanism of calcineurin activation was unclear These findings suggest that calcineurin signaling may be regulated through phosphorylation of MCIP1 by protein kinases. We sought initially to identify candidate kinases that activate calcineurin-NFAT signaling and to determine whether calcineurin/NFAT signaling is regulated through MCIP1 phosphorylation by the candidate kinases

Methods

Results

Conclusion