Platelet factor 4 selectively inhibits binding of TGF‐β1 to the type I TGF‐β1 receptor-猫眼课题宝

血小板因子 4 选择性抑制 TGF-β1 与 I 型 TGF-β1 受体的结合

DOI：

10.1002/jcb.240470105

发表时间：

1991

期刊：

Journal of Cellular Biochemistry

影响因子：

通讯作者：

中科院分区：

生物学2区

文献类型：

作者：

R. Whitson;W. L. Wong;K. Itakura

用Hep 3B肝癌细胞进行结合实验，在部分纯化的人血小板提取液中检测到一种低分子的转化生长因子-β1结合抑制物。对该抑制蛋白进行了纯化，根据其氨基酸序列鉴定为血小板因子4。100nM浓度的血小板第4因子可几乎完全抑制转化生长因子β1与Hep 3B细胞的结合，但对NRK49F成纤维细胞的结合仅有轻微抑制。亲和交联实验表明，血小板因子4抑制转化生长因子β1结合的差异是由于这两种细胞上存在的转化生长因子β1结合蛋白的补体不同所致。在Hep 3B细胞中，大部分结合的转化生长因子-β1与一个表观分子量为70 kDa的复合体交联。根据该蛋白的大小和结合特性，我们认为该蛋白为I型转化生长因子-β1受体。HEP 3B细胞也有一个高亲和力的转化生长因子-β1结合蛋白，呈现80 kDa的复合体，我们认为它是II型转化生长因子-β1受体。转化生长因子β1与该蛋白的结合不受血小板因子4的抑制。在Hep 3B细胞中，转化生长因子β1也与较高分子量的复合体发生了交联，但尚不清楚其中是否有代表III型转化生长因子β1受体。在NRK49F细胞中，大多数结合的转化生长因子-β1与一个可能代表III型转化生长因子-β1受体的高分子复合体交联。NRK49F细胞也有I型转化生长因子-β1受体，而血小板因子4抑制了与这些受体的结合。然而，由于I型受体只贡献了转化生长因子-β1结合的一小部分，因此，血小板因子4对转化生长因子-β1与NRK49F细胞结合的总体影响可以忽略不计。我们无法用直接结合或亲和交联法证明血小板第4因子与Hep 3B细胞的特异性或可饱和性结合。因此，尚不清楚血小板第4因子是否通过竞争结合I型受体来抑制转化生长因子-β1的结合。

A low molecular weight inhibitor of TGF‐β1 binding was detected in partially purified human platelet extracts by using Hep 3B hepatoma cells in the binding assays. The inhibitory protein was purified to homogeneity and was identified as platelet factor 4 on the basis of its amino acid sequence. TGF‐β1 binding to Hep 3B cells was almost completely inhibited by 100 nM concentrations of platelet factor 4, but TGF‐β1 binding to NRK 49F fibroblasts was inhibited only slightly. Affinity cross‐linking experiments revealed that these differences in the inhibition of TGF‐β1 binding by platelet factor 4 were due to differences in the complements of TGF‐β1 binding proteins present on these two cell types. In Hep 3B cells the majority of bound TGF‐β1 was cross‐linked to a complex which had an apparent molecular weight of 70 kDa. TGF‐β1 binding to this protein was the most sensitive to inhibition by platelet factor 4. Based on its size and TGF‐β1 binding properties, we believe this protein is the type I TGF‐β1 receptor. Hep 3B cells also had a high‐affinity TGF‐β1 binding protein which appeared as an 80 kDa complex, and which we believe to be the type II TGF‐β1 receptor. TGF‐β1 binding to this protein was not inhibited by platelet factor 4. TGF‐β1 was also cross‐linked to complexes of higher molecular weights in Hep 3B cells, but it was not clear whether any of them represented the type III TGF‐β1 receptor. In NRK 49F cells, the majority of bound TGF‐β1 was cross‐linked to a high molecular weight complex which probably represented the type III TGF‐β1 receptor. NRK 49F cells also had type I TGF‐β1 receptors and platelet factor 4 inhibited binding to these receptors in the NRK cells. Since the type I receptor contributed only a small percentage of total TGF‐β1 binding, however, the overall effects of platelet factor 4 on TGF‐β1 binding to NRK 49F cells were negligible. We were unable to demonstrate specific or saturable binding of platelet factor 4 to Hep 3B cells using either direct binding or affinity cross‐linking assays. Thus, it is not clear whether platelet factor 4 inhibits TGF‐β1 binding by competition for binding to the type I receptor.