Transcription activator which binds specifically to the MEF2 element present in the regulatory regions of many muscle-specific genes (PubMed:15862299). Controls cardiac morphogenesis and myogenesis, and is also involved in vascular development. Enhances transcriptional activation mediated by SOX18. Plays an essential role in hippocampal-dependent learning and memory by suppressing the number of excitatory synapses and thus regulating basal and evoked synaptic transmission. Crucial for normal neuronal development, distribution, and electrical activity in the neocortex. Necessary for proper development of megakaryocytes and platelets and for bone marrow B-lymphopoiesis. Required for B-cell survival and proliferation in response to BCR stimulation, efficient IgG1 antibody responses to T-cell-dependent antigens and for normal induction of germinal center B-cells. May also be involved in neurogenesis and in the development of cortical architecture (By similarity). Forms a complex with class II HDACs in undifferentiating cells. On myogenic differentiation, HDACs are released into the cytoplasm allowing MEF2s to interact with other proteins for activation. Interacts with EP300 in differentiating cells; the interaction acetylates MEF2C leading to increased DNA binding and activation. Interacts with HDAC7 and CARM1. Interacts with HDAC4 and HDAC9; the interaction with HDACs represses transcriptional activity. Interacts with LPIN1. Interacts with MYOCD. Interacts with AKAP13. Interacts with FOXK1; the interaction inhibits MEF2C transactivation activity (By similarity). Interacts (via N-terminus) with HABP4; this interaction decreases DNA-binding activity of MEF2C in myocardial cells in response to mechanical stress (PubMed:15862299). Interacts with JPH2; interaction specifically takes place with the Junctophilin-2 N-terminal fragment cleavage product of JPH2 (By similarity). Interacts (via MADS box) with SOX18 (By similarity). Expressed in the heart (PubMed:15862299). Expressed in cardiac myocytes (at protein level) (PubMed:15862299). The beta domain is required for enhancement of transcriptional activity. Phosphorylated on Ser-59; which enhances DNA binding activity. Phosphorylated on Ser-396; which is required for Lys-391 sumoylation and inhibits transcriptional activity. Acetylated by p300 on several sites in diffentiating myocytes. Acetylation on Lys-4 increases DNA binding and transactivation. Sumoylated on Lys-391 with SUMO2 but not SUMO1; which represses transcriptional activity. Proteolytically cleaved in cerebellar granule neurons on several sites by caspase 3 and caspase 7 following neurotoxicity. Preferentially cleaves the CDK5-mediated hyperphosphorylated form which leads to neuron apoptosis and transcriptional inactivation. Belongs to the MEF2 family.