Trans-regulation of myogenin promoter/enhancer activity by c-ski during skeletal-muscle differentiation: the C-terminus of the c-Ski protein is essential for transcriptional regulatory activity in myotubes

Abstract

c-ski gene product is a nuclear protein with myogenesis-promoting and transforming activities. We have analysed the effects of c-ski transfection on the promoter/enhancer activity of the upstream region of the myogenin gene during in vitro myogenesis using CAT reporter assay. When co-transfected with c-ski into myogenic C2C12 cells, promoter/enhancer activity was efficiently suppressed in proliferating cells, but the myogenesis-induced increase in activity was potentiated approximately ten times more (150-fold in the ski-transfected cells) than the ordinary increase (12-fold in the mock) 48 h after induction of differentiation. In non-myogenic 10T1/2 cells, c-ski transfection caused persistent suppression of promoter/enhancer activity in both proliferating and growth-arrested (i.e. myogenesis-inducing) conditions. Thus the ski-dependent potentiation of myogenin gene transcriptional activity appears to be specific for myogenesis. The C-terminal region (amino acids 595-663) of the c-Ski protein was essential for the potentiating activity in myotubes. Other members of the ski-gene family, snoN and snoA, were ineffective in transactivation, possibly because of the defect in the corresponding C-terminal region. c-Ski protein underwent a mobility shift on SDS/PAGE after in vitro myogenesis which may explain the conversion of the activity from suppressive in myoblasts to potentiating in myotubes. Deletion analysis of the upstream region of the myogenin gene revealed that a responsive element to c-ski in myotubes is located at a distinct site upstream of the basal promoter/enhancer region.

The Ski proto-oncogene regulates body composition and suppresses lipogenesis

“…15 Consistent with these observations, we show that Ski skeletal muscle expresses markedly increased levels of the mRNA encoding myogenin relative to WT muscle (Figure 4b). Moreover, we show differential effects in the c-Ski mice on other skeletal muscle factors, such as MEF2c and MyoD, with opposite effects on expression patterns of these myogenic regulators.…”

“…[20][21][22] Although several studies have examined the physiological effects of skeletal muscle hypertrophy in the Ski transgenic mouse, almost nothing is known about the mechanisms that mediate the decreased adiposity of these mice and whether Ski alters skeletal muscle metabolism or metabolic gene expression in target tissues, such as skeletal muscle or adipose tissue. 2 Moreover, although in vitro studies have identified several muscle-specific differentiation transcription factors that Ski regulates in the b-helix-loop-helix and MADS box protein family, such as MyoD and myogenin, 15,16 the role of c-Ski in modulation of other gene targets known to be involved in skeletal muscle hypertrophy has not been examined. Skeletal muscle accounts for B40% of the total body mass and energy expenditure.…”

“…14 The muscle regulatory factors with MEF2 family proteins coordinate the action of many different co-activators and co-repressors and signalling proteins (for example, p38 kinase) to control myogenesis. Nuclear Ski enhances muscle differentiation through modulation of myogenin promoter activity 15 through activation of the MyoD-myocyte enhancer factor 2 (MEF2) complex and inhibition of histone deacetylase activity. 16 Ski has also been reported to activate the enhancer/promoter of myosin light chain 1/3 and muscle creatine kinase.…”

Transformation of hematopoietic cells by the Ski oncoprotein involves repression of retinoic acid receptor signaling

“…Because of its nuclear localization and its ability to induce the expression of muscle-specific genes in quail cells (6), Ski has been assumed to be a transcription factor. Consistent with this assumption, c-Ski has been shown to bind DNA in vitro with the help of an unknown protein factor (13) and has been shown in muscle cells to enhance transactivation of reporter genes linked either to the myosin light-chain enhancer (14) or to a promoter͞enhancer element from the myogenin gene (15). Recently, Ski has been detected in association with the transcription factor nuclear factor 1 [also known as CCAAT-binding transcription factor 1 (CTF1)] and has been observed to potentiate the transactivation activity of nuclear factor 1 (16).…”

From insect eye to vertebrate muscle: redeployment of a regulatory network

“…Sno, like Ski, is expressed in many tissues, including neonatal and adult skeletal muscle (Pearson-White and Crittenden 1997). Although they have transforming activitiy, both Ski and Sno can convert muscle cells to myogenesis (Colmenares and Stavnezer 1989;Zheng et al 1997), and Ski potentiates transcription from the Myogenin promoter in differentiating muscle cells (Ichikawa et al 1997). Recently, it has been shown that Ski is a component of a histone deacetylase complex, modulating the effect on transcription of Mad and nuclear hormone receptors (Dahl et al 1998;Nomura et al 1999).…”