Regulation of the Myogenic Factor MEF2 by the mAKAP Complex.

摘要

Growth and repair of muscle requires a transition from proliferative myoblasts to functional, terminally differentiated myotubes capable of doing work. This process, known as myogenic differentiation, proceeds along a coordinated transcriptional trajectory that is temporally regulated. Myocyte enhancer factor 2 (MEF2) is necessary in this transcriptional cascade, and competing regulatory signaling networks converge on this protein, with no apparent coordination. Various kinases and phosphatases have been shown to either promote or halt myogenic differentiation through their actions on MEF2. In this way, a signal coordination problem exists: how does MEF2 interpret both positive and negative signals? The hypothesis of this work is that MEF2 associates with the muscle A-kinase anchoring protein (mAKAP) complex in order to achieve signal integration and coordinated transcriptional response to promote myogenic differentiation.;It was found that MEF2 and mAKAP do indeed associate via a direct interaction. Additionally, the expression of these proteins is increased during the early stages of differentiation, with a concomitant increase in MEF2 transcriptional activity. Interaction of MEF2 with mAKAP can be selectively disrupted, which blunts the differentiation-induced increase in MEF2 activity. Extended disruption of the interaction is deleterious to the morphogenesis of myotubes, with correspondent decreases in expression of MEF2 genetic targets. Mechanistically, it was found that disruption of calcineurin, a positive regulator of MEF2 and myogenic differentiation in general, from mAKAP elicited similar effects on MEF2 targets. It is therefore speculated that mAKAP provides a scaffold to which calcineurin and MEF2 can both bind, thereby enhancing the dephosphorylation step and providing for the full activation of MEF2 and induction of myogenic differentiation. This work describes a novel interaction between mAKAP and MEF2, and begins to provide a mechanism for the integration of signaling during myogenic differentiation.