Rabbit slow and fast skeletal muscle-derived satellite myoblast phenotypes do not involve constitutive differences in the components of the insulin-like growth factor system.

Barjot C; Navarro M; Cotten MLGarandel VBernardi HBacou FBarenton B

摘要

The insulin-like growth factor (IGF) system is actively involved in the control of proliferation and differentiation of several myogenic cell lines, and phenotypic differences between myoblasts are associated with modifications of the equilibrium of the components of the IGF system. To determine whether this observation is a physiologic feature that also concerns the phenotypes of ex vivo adult satellite myoblasts in primary cell culture, we investigated the IGF system in rabbit slow-twitch muscle-derived satellite myoblasts (SSM), which differ phenotypically from fast-twitch muscle-derived satellite myoblasts (FSM) by their proliferation and differentiation kinetics in vitro. The expression of IGF-I and IGF-II were similar in SSM and FSM as well as their concentrations measured in cell-conditioned media. Ligand blotting of conditioned media samples indicated the presence of five IGF binding protein (IGFBP) species of Mr 37-40, 32, 30-31, 28, and 24 kDa. The 30-31 kDa doublet was visible in SSM-conditioned medium only and associated with the presence of a 22-kDa protein, which may represent a proteolytic fragment. In contrast, the 32-kDa band was observed in FSM conditioned medium only. The other IGFBP moieties were present in both SSM- and FSM-conditioned media. Cross-linking experiments revealed the presence of the M6P/IGF-II receptor on both SSM and FSM membranes. We also observed an IGF-I receptor form bearing unusual high affinity for IGF-II: the binding of [125I]IGF-I on this receptor was preferentially displaced by IGF-I but that of [125I]IGF-II was mostly inhibited by IGF-II, suggesting that the two tracers did not bind on the same epitopes. [125I]IGF-II binding to this receptor was greater on SSM than on FSM membranes. Autophosphorylation of WGA-purified receptors revealed an approximately 400-kDa band after SDS-PAGE under nonreducing conditions, which corresponded to the alpha 2 beta 2 form of the IGF-I receptor, and two beta subunit moieties of Mr 101 and 105 kDa under reducing conditions in both SSM and FSM extracts. Phosphorylation of the 105-kDa moiety was more intensively increased than that of the 101-kDa protein after growth factor stimulation. Basal phosphorylation state of the two beta subunits was similarly stimulated by IGF-I and IGF-II and less by insulin. Since both insulin and IGF-I receptors were expressed in FSM and SSM, one of the two beta subunits may actually correspond to that of the insulin receptor. We conclude that the IGF system is not considerably affected by the phenotypes of SSM and FSM. The differences observed, which mostly concern IGFBP species, more likely appear as regulatory adaptations than as phenotypic changes targeting the components of the IGF system.

机译：胰岛素样生长因子(IGF)系统积极参与控制扩散和分化的细胞肌原性的行,和表型之间的差异成肌细胞与修改相关联的IGF的组件的平衡系统。一个生理特性,也涉及成肌细胞表型的体外成人卫星在主要的细胞培养,我们调查互联网管理论坛系统在兔子slow-twitch肌源性卫星肌母细胞(SSM)是不同的表型从增大肌源性卫星肌母细胞(FSM)的扩散和分化动力学体外。IGF-I和IGF-II相似的表情舰导弹和FSM以及他们的浓度以cell-conditioned媒体。印迹的媒体表示样品的五个胰岛素样生长因子结合蛋白(IGFBP)30 - 31种37-40先生,32岁,28岁,而24 kDa。30 - 31的kDa紧身上衣是可见的SSM-conditioned中只有和关联22-kDa蛋白质的存在,这可能代表一个蛋白水解片段。32-kDa乐队在FSM条件介质。在导弹和FSM-conditioned媒体。交联实验揭示了存在M6P / IGF-II受体对舰导弹和FSM膜。形式轴承不同寻常的高亲和力IGF-II:绑定[125 i] IGF-I的受体优先IGF-I但流离失所[125 i] IGF-II IGF-II主要是抑制,表明这两种示踪剂没有绑定相同的抗原表位。受体在FSM对舰导弹比膜。受体透露了一个大约400 kda乐队sds - page nonreducing条件下后,这与α2β2的形式IGF-I受体,和两个β亚基根先生的101年和105年减少条件下kDa在导弹和FSM提取物。105 kda的一部分更集中增加了比101 kda蛋白质后的增长因素刺激。的两个β亚基是同样的刺激通过IGF-I IGF-II和更少的胰岛素。胰岛素和IGF-I受体表达在FSM和导弹、两个β亚基之一实际对应的胰岛素受体。大大影响导弹的表型FSM和。关注IGFBP物种,更有可能出现监管适应性表型变化针对胰岛素样生长因子系统的组件。

Rabbit slow and fast skeletal muscle-derived satellite myoblast phenotypes do not involve constitutive differences in the components of the insulin-like growth factor system.

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