Riquelme C, Larrain J, Schonherr E, Henriquez J P, Kresse H, Brandan E
Centro de Regulación Celular y Patologia, Departamento de Biologia Celular y Molecular, Facultad de Ciencias Biológicas, MIFAB,P. Universidad Católica de Chile, P. O. Box 114-D, Santiago, Chile.
J Biol Chem. 2001 Feb 2;276(5):3589-96. doi: 10.1074/jbc.M004602200. Epub 2000 Nov 8.
Decorin is a member of the family of the small leucine-rich proteoglycans. In addition to its function as an extracellular matrix organizer, it has the ability to activate the epidermal growth factor receptor, and it forms complexes with various isoforms of transforming growth factor beta (TGF-beta). Decorin is expressed during skeletal muscle differentiation and is up-regulated in dystrophic muscle. In this study we investigated the role of decorin in TGF-beta-dependent inhibition of myogenesis. To probe the function of decorin during myogenesis, C(2)C(12) myoblasts were stably transfected with a plasmid expressing antisense decorin mRNA. The resulting inhibition of decorin expression led to the expression of myogenin, a master transcription factor for muscle differentiation, under growth conditions and accelerated skeletal muscle differentiation as determined by the expression of creatine kinase. In contrast myogenin expression was inhibited by adenovirally induced decorin expression or by adding exogenous decorin. Reduced synthesis of decorin resulted in a 7-fold decreased sensitivity to TGF-beta-mediated inhibition of myogenin expression. In contrast, adenovirally induced decorin expression in wild type cells resulted in a 5-fold increased sensitivity to TGF-beta-mediated inhibition of myogenin expression. Transfection studies with the TGF-beta-dependent promoter of the plasminogen activator inhibitor-1 coupled with luciferase revealed that the transducing receptors for TGF-beta1 and TGF-beta2 were involved in the different responses of wild type and antisense decorin myoblasts. These results demonstrate that a reduction of decorin expression or of decorin availability results in a decreased responsiveness to TGF-beta. These findings strongly suggest a new role for decorin during skeletal muscle terminal differentiation by activating TGF-beta-dependent signaling pathways.
核心蛋白聚糖是富含亮氨酸的小分子蛋白聚糖家族的成员。除了作为细胞外基质组织者的功能外，它还具有激活表皮生长因子受体的能力，并与转化生长因子β（TGF-β）的各种异构体形成复合物。核心蛋白聚糖在骨骼肌分化过程中表达，并在营养不良的肌肉中上调。在本研究中，我们研究了核心蛋白聚糖在TGF-β依赖性肌生成抑制中的作用。为了探究核心蛋白聚糖在肌生成过程中的功能，用表达反义核心蛋白聚糖mRNA的质粒稳定转染C(2)C(12)成肌细胞。由此导致的核心蛋白聚糖表达抑制导致在生长条件下肌细胞生成素（一种肌肉分化的主要转录因子）的表达，并通过肌酸激酶的表达确定加速了骨骼肌分化。相反，腺病毒诱导的核心蛋白聚糖表达或添加外源性核心蛋白聚糖抑制了肌细胞生成素的表达。核心蛋白聚糖合成减少导致对TGF-β介导的肌细胞生成素表达抑制的敏感性降低7倍。相反，腺病毒诱导野生型细胞中核心蛋白聚糖表达导致对TGF-β介导的肌细胞生成素表达抑制的敏感性增加5倍。用纤溶酶原激活物抑制剂-1的TGF-β依赖性启动子与荧光素酶进行的转染研究表明，TGF-β1和TGF-β2的转导受体参与了野生型和成肌细胞反义核心蛋白聚糖不同的反应。这些结果表明，核心蛋白聚糖表达或可用性的降低导致对TGF-β的反应性降低。这些发现强烈表明核心蛋白聚糖在骨骼肌终末分化过程中通过激活TGF-β依赖性信号通路发挥新的作用。
