MECHANISMS OF IGFBP5 STIMULATION OF BONE CELL FUNCTION

胰岛素样生长因子（IGFs）是一种蛋白质， 成骨细胞活性 IGF-I由成骨细胞分泌，因此可能 以自分泌的方式发挥作用以调节它们的功能。的因素 影响IGF-I的作用或产生，因此可能是 在骨疾病的发病机制和治疗中具有重要意义 以成骨细胞活性不活跃为特征。 igf结合蛋白 IGFBPs通过调节成骨样细胞的增殖和分化来影响成骨样细胞的功能。 IGF-I与其表面受体的结合。 已知IGFBP-5 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。 本独立 作用可能与其结合420 kDa成骨细胞的能力有关 在暴露于IGFBP-5时变得磷酸化的膜蛋白。 为了进一步研究IGFBP-5控制细胞凋亡的机制， 成骨细胞活性目前的建议将确定的身份， IGFBP-5-受体的表达克隆和建立 纯化和测序方法。成骨细胞转染 将使用IGFBP-5受体构建体和IGFBP-5受体抗体 建立受体与受体之间的结构-功能关系， 其磷酸化活性。 受体磷酸化也将是 其特征在于鉴定磷酸化结合位点和底物 特殊性 将进行结构研究， IGFBP-5和选择肽内化和核定位 将使用假定的核定位序列的取代 定义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， 改变这些过程的策略， 活性和改善骨质疏松症中有缺陷的骨形成。

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.