Duddy S K, Earp H S, Russell W E, Smith G J, Grisham J W
Department of Pathology, School of Medicine, University of North Carolina, Chapel Hill 27599, USA.
Cell Growth Differ. 1995 Mar;6(3):251-61.
The tumorigenic phenotype in rat liver epithelial cells overexpressing c-myc may depend on a transforming growth factor (TGF)-alpha/epidermal growth factor receptor autocrine loop (L. W. Lee et al., Cancer Res., 51: 5238-5244, 1991). In the present study, we have used constitutive sense and antisense TGF-alpha expression vectors to modify TGF-alpha production in carcinogen-transformed clonal derivatives of a rat liver epithelial cell line, WB-F344, that variably express c-myc, endogenous TGF-alpha, and tumorigenicity. Transgene-mediated TGF-alpha protein production was elevated 2- to 9-fold in derivatives of a low c-myc-expressing transformed cell line, GN4, and 35-fold in a derivative of a high c-myc-expressing cell line, GN6. Although the GN4- and GN6-derived cell lines expressed functional EGF receptor and steady-state c-myc mRNA levels that were comparable to their respective parental cell lines, increased TGF-alpha expression did not increase the tumorigenicity of the derivatives relative to the parental cell lines. Similarly, in vitro growth characteristics of the GN4- and GN6-derived cell lines were not markedly altered by increased autocrine TGF-alpha production. Additionally, GN4, GN6, and their derivatives were, for the most part, unresponsive to exogenously applied TGF-alpha in vitro. In contrast, antisense TGF-alpha RNA expression significantly suppressed endogenous TGF-alpha production in a high c-myc-expressing, high TGF-alpha-expressing, highly tumorigenic clonal line, GP9; this suppression resulted in lowered steady-state c-myc levels and attenuated in vitro growth. Antisense-mediated suppression of all of these in vitro phenotypes in GP9 was reversed by exogenous TGF-alpha. The latency of tumor formation by the antisense derivative of cell line GP9 was significantly lengthened (> 3-fold) relative to the time required for tumor formation by its parental cell line. These results demonstrate that a TGF-alpha/epidermal growth factor receptor autocrine loop may be necessary for exaggerated in vitro and in vivo growth of some transformed rat liver epithelial cells (e.g., GP9); however, the autocrine loop is not generally sufficient to support tumorigenicity, even in transformed clonal lines expressing elevated levels of c-myc.
在过表达c-myc的大鼠肝上皮细胞中，致瘤表型可能依赖于转化生长因子（TGF）-α/表皮生长因子受体自分泌环（L.W. Lee等人，《癌症研究》，51: 5238 - 5244，1991）。在本研究中，我们使用组成型正义和反义TGF-α表达载体来改变大鼠肝上皮细胞系WB-F344的致癌物转化克隆衍生物中TGF-α的产生，该细胞系可变地表达c-myc、内源性TGF-α和致瘤性。在低c-myc表达的转化细胞系GN4的衍生物中，转基因介导的TGF-α蛋白产生提高了2至9倍，在高c-myc表达的细胞系GN6的衍生物中提高了35倍。尽管源自GN4和GN6的细胞系表达功能性表皮生长因子受体以及与各自亲代细胞系相当的稳态c-myc mRNA水平，但相对于亲代细胞系，TGF-α表达的增加并未增加衍生物的致瘤性。同样，源自GN4和GN6的细胞系的体外生长特性并未因自分泌TGF-α产生的增加而明显改变。此外，GN4、GN6及其衍生物在体外大多对外源施加的TGF-α无反应。相反，反义TGF-α RNA表达显著抑制了高c-myc表达、高TGF-α表达、高致瘤性克隆系GP9中的内源性TGF-α产生；这种抑制导致稳态c-myc水平降低并减弱了体外生长。外源TGF-α逆转了反义介导的对GP9中所有这些体外表型的抑制。相对于其亲代细胞系形成肿瘤所需的时间，细胞系GP9的反义衍生物形成肿瘤的潜伏期显著延长（>3倍）。这些结果表明，TGF-α/表皮生长因子受体自分泌环对于某些转化的大鼠肝上皮细胞（如GP9）在体外和体内的过度生长可能是必需的；然而，即使在表达升高水平c-myc的转化克隆系中，自分泌环通常也不足以支持致瘤性。
