Collaborative interactions between MEF-2 and Sp1 in muscle-specific gene regulation

Abstract

Previous investigations have demonstrated synergistic interactions in vivo between CCAC and A/T-rich nucleotide sequence motifs as functional components of muscle-specific transcriptional enhancers. Using CCAC and A/T-rich elements from the myoglobin and muscle creatine kinase (MCK) gene enhancers, Sp1 and myocyte-specific enhancer factor-2 (MEF-2) were identified as cognate binding proteins that recognize these sites. Physical interactions between Sp1 and MEF-2 were demonstrated by immunological detection of both proteins in DNA binding complexes formed in vitro by nuclear extracts in the presence of only the A/T sequence motif, by coprecipitation of recombinant MEF-2 in the presence of a glutathione-S-transferase-Sp1 fusion protein bound to glutathione beads, and by a two-hybrid assay in Saccharomyces cerevisiae. The interaction with Sp1 in vitro and in vivo is specific for MEF-2 and was not observed with serum response factor, a related MADS domain protein. Forced expression of Sp1 and MEF-2 in insect cells otherwise lacking these factors promotes synergistic transcriptional activation of a promoter containing binding sites for both proteins. These data expand the repertoire of functional and physical interactions between lineage-restricted (MEF-2) and ubiquitous (Sp1) transcription factors that may be important for myogenic differentiation.

CORECLUST: identification of the conserved CRM grammar together with prediction of gene regulation

“…Interestingly, according to the model, the intersite distance for the site pair Mef2-Myf is distributed according to the helical phasing distribution, which was also observed in (25). The other observed interactions are also supported by the literature or TransCompel: Tef-Mef2 (40), Myf-Sp1 (36) and Mef2-Sp1 (41). …”

Regulation of muscle regulatory factors by DNA-binding, interacting proteins, and post-transcriptional modifications

“…This functional crosstalk has been molecularly explained by a direct interaction between the myogenic bHLH/E12 heterodimers with SRF (Groisman et al, 1996). Similarly, Sp1 associates with myogenic bHLH (Biesiada et al, 1999) and MEF2 (Grayson et al, 1998) proteins, and Sp-1 sites are frequently found to be necessary for activation of muscle gene expression (Gustafson and Kedes, 1989;Sartorelli et al, 1990). Consistent with their positive role in muscle gene expression, myogenic bHLH, SRF, and Sp1 are found on a muscle-specific transcriptional complex (Biesiada et al, 1999).…”

Activation of MEF2 by muscle activity is mediated through a calcineurin-dependent pathway

“…Relationships between the enzymatic activity of calcineurin in hindlimb muscles and expression of myoglobin and troponin I slow, endogenous genes known to be controlled by MEF2 activity (Grayson et al ., 1998; Wu et al ., 2000; Yan et al ., 2001) and induced by exercise or motor nerve stimulation (Underwood and Williams, 1987) were assessed by the comparison of five independent lines of transgenic mice engineered to express a constitutively active form of calcineurin under the control of the MCK promoter. Three different transgene constructions were used, as shown in Figure 6A.…”