Pdcd4 suppresses tumor phenotype in JB6 cells by inhibiting AP-1 transactivation

• Published in: Oncogene Vol. 22; no. 24; pp. 3712 - 3720
• Main Authors: YANG, Hsin-Sheng, KNIES, Jennifer L, STARK, Cristi, COLBURN, Nancy H
• Format: Journal Article
• Language: English
• Published: Basingstoke Nature Publishing 12.06.2003; Nature Publishing Group
• Subjects: Activator protein 1; Animals; Apoptosis Regulatory Proteins; Biological and medical sciences; c-Fos protein; c-Jun protein; Cancer research; Cell Division; Cell physiology; Cell transformation and carcinogenesis. Action of oncogenes and antioncogenes; Cell Transformation, Neoplastic; Cells, Cultured; Colonies; Down-Regulation; Electrophoretic mobility; Fra1 protein; Fundamental and applied biological sciences. Psychology; Genetic transformation; Genotype & phenotype; JunB protein; Medical research; Mice; Molecular and cellular biology; Phenotypes; Proteins - physiology; Proto-Oncogene Proteins c-fos - antagonists & inhibitors; Proto-Oncogene Proteins c-jun - antagonists & inhibitors; Reporter gene; Response Elements - physiology; RNA-Binding Proteins; Transcription activation; Transcription Factor AP-1 - antagonists & inhibitors; Transcription Factor AP-1 - biosynthesis; Transcription factors; Transcriptional Activation; Transfection; c-Jun; Phenotype; c-Fos; Pdcd4; transformation; AP-1; Tumor cell
• ISSN: 0950-9232; 1476-5594
• DOI: 10.1038/sj.onc.1206433

Transformation suppressor Pdcd4 is downregulated in transformed (Tx) mouse epidermal JB6 RT101 cells relative to transformation-resistant (P-) and susceptible (P+) variants. Whether Pdcd4 downregulation is necessary not only to induce transformation but also to maintain tumor phenotypes has not been determined previously. In the present study, overexpression of Pdcd4 cDNA in stably transfected RT101 cells resulted in 40% fewer anchorage-independent colonies that were smaller in size than the vector control colonies, indicating that elevated Pdcd4 expression is sufficient to suppress tumor phenotype. Transient transfection of Pdcd4 expression plasmid and 4 x AP-1 reporter gene showed that activation of AP-1-dependent transcription was inhibited by Pdcd4 expression in a concentration-dependent manner. In contrast, Pdcd4 did not inhibit serum response element-dependent transcription, indicating specificity. In a Gal4 fusion assay, Pdcd4 specifically inhibited activation of c-Jun and c-Fos activation domains, but did not inhibit activation of JunB, JunD, Fra-1, or Fra-2. Gel mobility shift assay demonstrated that c-Jun is the major component detected in the AP-1 complex in RT101 cells. Previous studies suggested that AP-1 activity is required for maintaining the transformed phenotype in RT101 cells. Thus, Pdcd4 suppresses tumor phenotype by inhibiting AP-1-dependent transcription, possibly through inhibiting c-Jun and c-Fos activation.