Bywater M, Rorsman F, Bongcam-Rudloff E, Mark G, Hammacher A, Heldin C H, Westermark B, Betsholtz C
Department of Pathology, University Hospital, Uppsala, Sweden.
Mol Cell Biol. 1988 Jul;8(7):2753-62. doi: 10.1128/mcb.8.7.2753-2762.1988.
The autocrine effects of platelet-derived growth factor (PDGF) A- and B-chain homodimers (PDGF-AA and PDGF-BB) on rat-1 cells and human fibroblasts have been investigated by using human PDGF A- and B-chain cDNA clones expressed in a retroviral vector. Infection with replication-defective virus carrying the B-chain cDNA resulted in a phenotypical transformation resembling that induced by simian sarcoma virus. The resulting cells were focus forming in monolayer cultures, grew to high saturation densities, and formed large colonies in soft agar. The PDGF A-chain transfectants showed no transformed morphology and lacked focus-forming activity but grew to high saturation density in monolayer culture and formed small colonies in soft agar. A similar but weaker effect was obtained with an A-chain cDNA variant containing a 69-base-pair insertion in the 3' end of the protein-coding domain. A- and B-chain transfectants released PDGF receptor-competing activity into the medium, but only the medium conditioned by the B-chain transfectants possessed potent mitogenic activity on human fibroblasts. Both types of transfectants had downregulated levels of PDGF receptors; however, the B-chain transfectants were downregulated to significantly lower levels. Metabolic labeling and immunoprecipitations with PDGF antiserum showed that the PDGF B-chain protein was processed to a 24-kilodalton cell-associated and a 30-kilodalton secreted dimeric protein. The A-chain protein was rapidly secreted as a 31-kilodalton dimeric protein. The present study shows a marked difference in the autocrine effects of PDGF-AA and -BB expressed under the control of a retroviral promoter and suggests that different biological properties may be assigned to these two PDGF isoforms.
利用在逆转录病毒载体中表达的人血小板衍生生长因子（PDGF）A链和B链cDNA克隆，研究了PDGF A链和B链同二聚体（PDGF-AA和PDGF-BB）对大鼠-1细胞和人成纤维细胞的自分泌作用。用携带B链cDNA的复制缺陷型病毒感染，导致了一种类似于猿猴肉瘤病毒诱导的表型转化。所产生的细胞在单层培养中形成集落，生长至高密度饱和状态，并在软琼脂中形成大菌落。PDGF A链转染细胞未显示转化形态，缺乏集落形成活性，但在单层培养中生长至高密度饱和状态，并在软琼脂中形成小菌落。在蛋白质编码结构域3'端含有69个碱基对插入的A链cDNA变体也获得了类似但较弱的效应。A链和B链转染细胞将PDGF受体竞争性活性释放到培养基中，但只有B链转染细胞条件培养基对人成纤维细胞具有强大的促有丝分裂活性。两种类型的转染细胞中PDGF受体水平均下调；然而，B链转染细胞下调至显著更低水平。用PDGF抗血清进行代谢标记和免疫沉淀显示，PDGF B链蛋白被加工成一种24千道尔顿的细胞相关二聚体蛋白和一种30千道尔顿的分泌性二聚体蛋白。A链蛋白迅速作为一种31千道尔顿的二聚体蛋白分泌。本研究显示了在逆转录病毒启动子控制下表达的PDGF-AA和-BB自分泌作用的显著差异，并表明这两种PDGF异构体可能具有不同的生物学特性。
