IMPACT OF MUTANT COMP ON SECRETION IN CHONDRYOCYLES

两种人类侏儒症，假性软骨发育不全（PRACH）和多发性骨骺发育不良（MED），是由软骨寡聚基质蛋白（COMP）突变引起的。 在PSACH软骨细胞中，COMP突变导致形成异常大的粗面内质网（RER），具有独特的指纹外观。 位于这些囊泡内的是COMP和IX型胶原。这些异常的囊泡没有发现在肌腱成纤维细胞，虽然这些细胞分泌COMP。这个建议的目的是阐明背后的COMP和IX型胶原蛋白在软骨细胞，但不是在肌腱成纤维细胞异常保留的分子机制。 根据最近的研究提出了以下假设：突变的COMP分子保留在软骨细胞的粗面内质网中，因为III型重复序列没有正确折叠，从而导致非天然二硫键的形成。 然后，这些分子在组装过程中与软骨细胞特异性RER分子和/或与天然IX型胶原和/或IX型胶原链相互作用。 这种非天然的复合物不能分泌，并导致在软骨细胞RER内的层状结构中积累。 突变COMP的分泌发生在成纤维细胞和去分化软骨细胞中，因为这些细胞不合成IX型胶原或不含有软骨细胞特异性RER蛋白。 提出了具体的目标，以确定正常和突变的血小板反应蛋白III型重复的结构，定义在这些重复的二硫键和钙对结构的影响，并测试与IX型胶原和未折叠的IX型胶原链和REER蛋白的软骨细胞的突变COMP的结合相互作用。

Two human dwarfing disorders, pseudoachondroplasia (PSACH) and multiple epiphyseal dysplasia (MED), are caused by mutations in cartilage oligomeric matrix protein (COMP). In PSACH chondrocytes, mutations in COMP lead to the formation of abnormally large rough endoplasmic reticulum (RER) with a unique fingerprint appearance. Located within these vesicles are COMP and type IX collagen. These abnormal vesicles are not found in tendon fibroblasts, although these cells secrete COMP. This proposal is aimed at elucidating the molecular mechanism behind the abnormal retention of COMP and type IX collagen in chondrocytes but not in tendon fibroblasts. The following hypotheses were developed from recent studies: Mutant COMP molecules are retained in the RER of chondrocytes because the type III repeats do not fold properly, which leads to the formation of non-native disulfide bonds. These molecules are then interacting with either chondrocyte specific RER molecules and/or with native type IX collagen and/or type IX collagen chains in the process of assembly. This non-native complex cannot be secreted and leads to the accumulation in lamellar structures within the RER of chondrocytes. Secretion of mutant COMP occurs in fibroblasts and dedifferentiated chondrocytes, because these cells do not synthesize type IX collagen or do not contain chondrocyte specific RER proteins. Specific aims are proposed to determine the structure of normal and mutant thrombospondin type III repeats, to define the disulfide linkages in these repeats and the effects of calcium on structure, and to test binding interactions of mutant COMP with type IX collagen and unfolded type IX collagen chains and with REER proteins of chondrocytes.