Jiang D, Liang J, Humphrey L E, Yang H, Brattain M G
Department of Biochemistry and Molecular Biology, Medical College of Ohio, Toledo, USA.
J Cell Physiol. 1998 May;175(2):174-83. doi: 10.1002/(SICI)1097-4652(199805)175:2<174::AID-JCP7>3.0.CO;2-L.
Autocrine transforming growth factor alpha (TGFalpha) activity and control mechanisms for its expression were examined in a representative clonal isolate (CBS4) of a well-differentiated human colon carcinoma cell line designated CBS. CBS4 cells expressed TGFalpha and its receptor, epidermal growth factor receptor (EGFr). Blockade of EGFr and TGFalpha by neutralizing antibodies inhibited clonal growth and the initiation of DNA synthesis from quiescence in CBS4 cells. Therefore, TGFalpha is an autocrine growth factor for CBS4 cells. Several studies have indicated that activation of the EGFr by exogenous EGF stimulates TGFalpha expression. However, in CBS4 cells EGF did not induce TGFalpha mRNA expression, indicating that EGF does not affect TGFalpha transcription in these cells. Exogenous treatment of exponentially growing cells with either EGF or EGFr blocking antibody enhanced release of TGFalpha protein into the conditioned medium. This indicated that the release of TGFalpha into the conditioned medium by exogenous EGF was at least partially due to the displacement of TGFalpha from the TGFalpha/EGFr complexes. Similarly to exponentially growing cells, the EGFr blocking antibody and EGF also enhanced TGFalpha release into the medium of CBS4 cells after release from quiescence. These results indicated that exogenous EGF had little if any effect on TGFalpha expression in these cells and suggested that TGFalpha expression might be under endogenous TGFalpha control. Blockade of the autocrine TGFalpha loop by TGFalpha neutralizing antibody suppressed TGFalpha mRNA both in exponentially growing and quiescent cells, demonstrating that autocrine TGFalpha is autoregulatory in this system.
在一种名为CBS的高分化人结肠癌细胞系的代表性克隆分离株（CBS4）中，研究了自分泌转化生长因子α（TGFα）的活性及其表达的调控机制。CBS4细胞表达TGFα及其受体表皮生长因子受体（EGFr）。用中和抗体阻断EGFr和TGFα可抑制CBS4细胞的克隆生长以及从静止状态启动DNA合成。因此，TGFα是CBS4细胞的自分泌生长因子。多项研究表明，外源性表皮生长因子（EGF）激活EGFr可刺激TGFα表达。然而，在CBS4细胞中，EGF并未诱导TGFα mRNA表达；这表明EGF不影响这些细胞中TGFα的转录。用EGF或EGFr阻断抗体对外源性处理指数生长期的细胞，可增强TGFα蛋白释放到条件培养基中。这表明外源性EGF使TGFα释放到条件培养基中，至少部分是由于TGFα从TGFα/EGFr复合物中被置换出来。与指数生长期的细胞类似，EGFr阻断抗体和EGF在CBS4细胞从静止状态释放后，也增强了TGFα释放到培养基中。这些结果表明，外源性EGF对这些细胞中TGFα的表达几乎没有影响，并提示TGFα的表达可能受内源性TGFα的调控。用TGFα中和抗体阻断自分泌TGFα环路，可抑制指数生长期和静止期细胞中的TGFα mRNA，这表明在该系统中自分泌TGFα具有自我调节作用。
