Amstad P A, Liu H, Ichimiya M, Chang S, Berezesky I K, Trump B F
Department of Pathology, University of Maryland, Baltimore 21201, USA.
Mol Carcinog. 1997 Oct;20(2):231-9. doi: 10.1002/(sici)1098-2744(199710)20:2<231::aid-mc10>3.0.co;2-b.
Increased bcl-2 expression is a common feature of many types of human malignancies, which implies that bcl-2 plays an important role in tumorigenesis. To better understand the molecular mechanisms of bcl-2-induced oncogenesis, we examined the effects of bcl-2 expression on transformation of mouse epidermal JB6 cells induced by the tumor promoter 12-O-tetradecanoylphorbol-13 acetate (TPA). Promotion-sensitive JB6 clone41 cells were transfected with the bcl-2-containing expression vector pD5-neo/bcl-2, and the soft agar growth of bcl-2-transfected cells and control cells were compared. bcl-2 overexpression in JB6 clone41 cells caused a TPA-induced soft-agar growth fivefold greater than the growth of nontransfected or vector-transfected (neo control) cells. bcl-2 expression in the absence of TPA did not lead to colony formation in soft agar. Because the level of the transcription factor activator protein 1 (AP-1) has been shown to be critical for the responsiveness of JB6 cells to TPA-induced transformation, we compared c-jun and c-fos expression as well as the AP-1-binding activity and the AP-1-mediated transactivation of the reporter construct TRE-CAT between bcl-2-expressing cells and control cells. When compared with control cells, bcl-2-transfected cells expressed significantly more c-fos but not c-jun after TPA treatment. Furthermore, the levels of AP-1 and AP-1-induced transactivation of TRE-CAT were greater in bcl-2-transfected cells than in control cells after TPA treatment. These results showed that bcl-2 cooperates with a tumor promoter such as TPA in the induction of malignant transformation in mouse epidermal cells and that bcl-2 enhances soft-agar growth by stimulating signaling pathways that led to increased AP-1 expression.
bcl-2表达增加是多种人类恶性肿瘤的共同特征，这表明bcl-2在肿瘤发生中起重要作用。为了更好地理解bcl-2诱导肿瘤发生的分子机制，我们检测了bcl-2表达对肿瘤启动子12-O-十四酰佛波醇-13-乙酸酯（TPA）诱导的小鼠表皮JB6细胞转化的影响。将对促进作用敏感的JB6克隆41细胞用含bcl-2的表达载体pD5-neo/bcl-2进行转染，并比较bcl-2转染细胞和对照细胞在软琼脂中的生长情况。JB6克隆41细胞中bcl-2的过表达导致TPA诱导的软琼脂生长比未转染或载体转染（neo对照）细胞的生长大五倍。在没有TPA的情况下，bcl-2表达不会导致软琼脂中的集落形成。因为转录因子激活蛋白1（AP-1）的水平已被证明对JB6细胞对TPA诱导的转化的反应性至关重要，所以我们比较了bcl-2表达细胞和对照细胞之间c-jun和c-fos的表达以及AP-1结合活性和报告基因构建体TRE-CAT的AP-1介导的反式激活。与对照细胞相比，bcl-2转染细胞在TPA处理后表达的c-fos明显更多，但c-jun没有增加。此外，在TPA处理后，bcl-2转染细胞中AP-1和AP-1诱导的TRE-CAT反式激活水平高于对照细胞。这些结果表明，bcl-2与肿瘤启动子如TPA协同作用诱导小鼠表皮细胞的恶性转化，并且bcl-2通过刺激导致AP-1表达增加的信号通路增强软琼脂生长。
