MECHANISMS OF IGFBP5 STIMULATION OF BONE CELL FUNCTION

胰岛素样生长因子(IGF)是一种刺激 成骨细胞活性。IGF-I由成骨细胞分泌，因此可能 以一种自分泌的方式来调节它们的功能。影响因素 因此，影响IGF-I的作用或产生的可能是 在骨病的发病机制和治疗中的重要作用 以不活跃的成骨细胞活动为特征。胰岛素样生长因子结合蛋白 (IGFBPs)通过影响成骨样细胞的功能 IGF-I与其表面受体的结合。IGFBP-5已知为 增强IGF-I对成骨细胞活性的刺激，此外， 对成骨细胞功能有独立的影响。这是独立的 其作用可能与其与420 kDa成骨细胞结合的能力有关 暴露于IGFBP-5后发生磷酸化的膜蛋白。 为了进一步研究IGFBP-5控制的机制 成骨细胞的活动目前的提议将确定身份 通过表达克隆和建立IGFBP-5受体 纯化和测序方法。转染成骨细胞的成骨细胞 将使用IGFBP-5受体构建和IGFBP-5受体抗体 建立受体和受体之间的结构-功能关系 它的磷酸化活性。受体的磷酸化也将是 其特征在于鉴定了磷酸化结合部位和底物 具体细节。将进行结构研究，以评估 IGFBP-5及其选择性多肽的内化和核定位 将使用假定的核定位序列的替换 确定核运输的最低结构要求 IGFBP-5。这些研究的结果应该定义新的机制 其中IGFBP-5刺激成骨细胞功能并可能提示 以增强成骨细胞的方式改变这些过程的策略 改善骨质疏松中有缺陷的骨形成。

Insulin-like growth factors (IGFs) are proteins that stimulate osteoblast activity. IGF-I is secreted by osteoblasts and so may function in an autocrine manner to regulate their function. Factors that affect the action or production of IGF-I are therefore likely to be important in the pathogenesis and treatment of bone diseases characterized by inactive osteoblast activity. IGF-binding proteins (IGFBPs) affect the function of osteoblast-like cells by modulating the binding of IGF-I with its surface receptor. IGFBP-5 is known to enhance IGF-I stimulation of osteoblast activity and in addition, to have independent effects on osteoblast function. This independent effect may be related to its ability to bind to a 420 kDa osteoblast membrane protein which becomes phosphorylated upon exposure to IGFBP-5. To further investigate the mechanisms in which IGFBP-5 controls osteoblast activity the current proposal will determine the identity of the IGFBP-5-receptor by expression cloning and by established purification and sequencing methods. Osteoblasts transfected with IGFBP-5-receptor constructs and IGFBP-5-receptor antibodies will be used to establish structure-function relationships between the receptor and its phosphorylating activities. Receptor phosphorylation will also be characterized by identifying phosphorylation binding sites and substrate specificities. Structural studies will be conducted to assess internalization and nuclear localization of IGFBP-5 and selected peptide substitutions of the putative nuclear localization sequence will be used to define minimum structural requirements for the nuclear transport of IGFBP-5. The results of these studies should define novel mechanisms in which IGFBP-5 stimulates osteoblast function and may suggest strategies to alter these processes in ways that enhance osteoblast activity and improve defective bone formation in osteoporosis.