Dhar Arindam, Hu Jing, Reeves Raymond, Resar Linda M S, Colburn Nancy H
Gene Regulation Section, Laboratory of Cancer Prevention, NCI at Frederick, Frederick, MD 21702-1201, USA.
Oncogene. 2004 May 27;23(25):4466-76. doi: 10.1038/sj.onc.1207581.
Activation of the transcription factor AP-1 (activator protein-1) is required for tumor promotion and maintenance of malignant phenotype. A number of AP-1-regulated genes that play a role in tumor progression have been identified. However, AP-1-regulated genes driving tumor induction are yet to be defined. Previous studies have established that expression of a dominant-negative c-Jun (TAM67) inhibits phorbol 12-tetradecanoyl-13-acetate (TPA)-induced AP-1 transactivation as well as transformation in mouse epidermal JB6/P+ cells and tumor promotion in mouse skin carcinogenesis. In this study, we utilized the tumor promotion-sensitive JB6/P+ cells to identify AP-1-regulated TAM67 target genes and to establish causal significance in transformation for one target gene. A 2700 cDNA microarray was queried with RNA from TPA-treated P+ cells with or without TAM67 expression. Under conditions in which TAM expression inhibited TPA-induced transformation, microarray analysis identified a subset of six genes induced by TPA and suppressed by TAM67. One of the identified genes, the high-mobility group protein A1 (Hmga1) is induced by TPA in P+, but not in transformation-resistant P cells. We show that TPA induction of the architectural transcription factor HMGA1 is inhibited by TAM67, is extracellular-signal-regulated kinase (ERK)-activation dependent, and is mediated by AP-1. HMGA1 antisense construct transfected into P+ cells blocked HMGA1 protein expression and inhibited TPA-induced transformation indicating that HMGA1 is required for transformation. HMGA1 is not however sufficient as HMGA1a or HMGA1b overexpression did not confer transformation sensitivity on P- cells. Although HMGA1 expression is ERK dependent, it is not the only ERK-dependent event required for transformation because it does not suffice to rescue ERK-deficient P- cells. Our study shows (a) TAM 67 when it inhibits AP-1 and transformation, targets a relatively small number of genes; (b) HMGA1, a TAM67 target gene, is causally related to transformation and therefore a potentially important target for cancer prevention.
转录因子AP-1（激活蛋白-1）的激活是肿瘤促进和恶性表型维持所必需的。已鉴定出许多在肿瘤进展中起作用的AP-1调节基因。然而，驱动肿瘤诱导的AP-1调节基因尚未明确。先前的研究表明，显性负性c-Jun（TAM67）的表达可抑制佛波酯12-十四烷酰-13-乙酸酯（TPA）诱导的AP-1反式激活以及小鼠表皮JB6/P+细胞中的转化和小鼠皮肤致癌过程中的肿瘤促进作用。在本研究中，我们利用对肿瘤促进敏感的JB6/P+细胞来鉴定AP-1调节的TAM67靶基因，并确定一个靶基因在转化中的因果意义。用来自有或没有TAM67表达的TPA处理的P+细胞的RNA查询一个2700 cDNA微阵列。在TAM表达抑制TPA诱导的转化的条件下，微阵列分析鉴定出由TPA诱导并被TAM67抑制的六个基因的一个子集。鉴定出的基因之一，高迁移率族蛋白A1（Hmga1）在P+细胞中被TPA诱导，但在抗转化的P细胞中不被诱导。我们表明，结构转录因子HMGA1的TPA诱导被TAM67抑制，是细胞外信号调节激酶（ERK）激活依赖性的，并由AP-1介导。转染到P+细胞中的HMGA1反义构建体阻断了HMGA1蛋白表达并抑制了TPA诱导的转化，表明HMGA1是转化所必需的。然而，HMGA1并不充分，因为HMGA1a或HMGA1b的过表达并未赋予P-细胞转化敏感性。虽然HMGA1的表达是ERK依赖性的，但它不是转化所需的唯一ERK依赖性事件，因为它不足以挽救ERK缺陷的P-细胞。我们的研究表明：（a）TAM 67在抑制AP-1和转化时，靶向相对少数的基因；（b）HMGA1，一个TAM67靶基因，与转化有因果关系，因此是癌症预防的一个潜在重要靶点。
