Liu Xin-Hua, De Gasperi Rita, Bauman William A, Cardozo Christopher P
National Center for the Medical Consequences of Spinal Cord Injury, James J. Peter VA Medical Center, Bronx, New York.
Department of Medicine, Icahn School of Medicine at Mount Sinai, New York, New York.
Physiol Rep. 2018 Jan;6(1). doi: 10.14814/phy2.13520.
Signaling via the androgen receptor (AR) stimulates myogenic progenitor differentiation. In addition, myogenic differentiation factor D (MyoD) and Numb, a Notch inhibitor, play key roles in regulating myogenic differentiation. Nandrolone, an anabolic steroid, upregulates both MyoD and Numb expression in myogenic cells. However, the molecular mechanisms by which MyoD is upregulated by nandrolone are unclear. Moreover, the potential crosstalk between nandrolone, MyoD, and Numb is not well understood. With these considerations in mind, we examined the effects of nandrolone on the expression of MyoD mRNA and protein, and determined the interactions of MyoD and Numb in the presence or absence of nandrolone in differentiating C2C12 myoblasts. Nandrolone increased MyoD mRNA and protein expression and significantly enhanced nuclear translocation of MyoD protein. The later effect of nandrolone was blunted by siRNA against Numb. Immunoprecipitation (IP) studies confirmed that Numb forms complexes with MyoD. Chromatin IP revealed that in the presence of nandrolone, Numb is recruited to a region of the MyH7 promotor containing the E-box to which MyoD binds. These data indicate that nandrolone-regulated MyoD activation occurs mainly through a posttranslational mechanism which promotes MyoD nuclear accumulation, and suggest that this effect of nandrolone is, at least in part, mediated by Numb.
通过雄激素受体（AR）发出的信号刺激成肌祖细胞分化。此外，成肌分化因子D（MyoD）和Notch抑制剂Numb在调节成肌分化中起关键作用。合成代谢类固醇诺龙可上调成肌细胞中MyoD和Numb的表达。然而，诺龙上调MyoD的分子机制尚不清楚。此外，诺龙、MyoD和Numb之间潜在的相互作用也未得到充分了解。考虑到这些因素，我们研究了诺龙对MyoD mRNA和蛋白表达的影响，并确定了在分化的C2C12成肌细胞中存在或不存在诺龙的情况下MyoD和Numb的相互作用。诺龙增加了MyoD mRNA和蛋白表达，并显著增强了MyoD蛋白的核转位。针对Numb的小干扰RNA（siRNA）减弱了诺龙的后期作用。免疫沉淀（IP）研究证实Numb与MyoD形成复合物。染色质免疫沉淀显示，在存在诺龙的情况下，Numb被招募到MyH7启动子中含有MyoD结合的E盒的区域。这些数据表明，诺龙调节的MyoD激活主要通过促进MyoD核积累的翻译后机制发生，并表明诺龙的这种作用至少部分是由Numb介导的。
