Differentially expressed protein Pdcd4 inhibits tumor promoter-induced neoplastic transformation

• DOI: 10.1073/pnas.96.24.14037
• Publication Date: 2002-07-26T14:35:07Z
• Authors: Joan L. Cmarik; Hongzhong Min; Glenn Hegamyer; Shuning Zhan; Molly Kulesz-Martin; Hidetoshi Yoshinaga; Sachiko Matsuhashi; Nancy H. Colburn
• Keywords: Keratinocytes; 0301 basic medicine; Mice, Inbred BALB C; Immunoblotting; Gene Expression; Proteins; RNA-Binding Proteins; Cell Line; Mice; 03 medical and health sciences; Cell Transformation, Neoplastic; Phenotype; Protein Biosynthesis; Tumor Cells, Cultured; Animals; Humans; Tetradecanoylphorbol Acetate; RNA, Messenger; Rabbits; Apoptosis Regulatory Proteins

An mRNA differential display comparison of mouse JB6 promotion-sensitive (P+) and -resistant (P−) cells identified a novel gene product that inhibits neoplastic transformation. The JB6 P+ and P− cells are genetic variants that differ in their transformation response to tumor promoters; P+ cells form anchorage-independent colonies that are tumorigenic, and P− cells do not. A differentially displayed fragment,A7-1, was preferentially expressed in P− cells at levels ≥10-fold those in P+ cells, making its mRNA a candidate inhibitor of neoplastic transformation. AnA7-1cDNA was isolated that was identical to murinePdcd4gene cDNAs, also known asMA-3orTIS, and analogous to humanH731and197/15a. Until now, the function of the Pdcd4 protein has been unknown. Paralleling the mRNA levels, Pdcd4 protein levels were greater in P− than in P+ cells.Pdcd4mRNA was also expressed at greater levels in the less progressed keratinocytes of another mouse skin neoplastic progression series. To test the hypothesis that Pdcd4 inhibits tumor promoter-induced transformation, stable cell lines expressing antisensePdcd4were generated from parental P− cells. The reduction of Pdcd4 proteins in antisense lines was accompanied by acquisition of a transformation-sensitive (P+) phenotype. The antisense-transfected cells were reverted to their initial P− phenotype by overexpression of aPdcd4sense fragment. These observations demonstrate that the Pdcd4 protein inhibits neoplastic transformation.