title: 14-3-3 sigma positively regulates p53 and suppresses tumor growth.
abstract: The 14-3-3 sigma (sigma) protein, a negative regulator of the cell cycle, is a human mammary epithelium-specific marker that is downregulated in transformed mammary carcinoma cells. It has also been identified as a p53-inducible gene product involved in cell cycle checkpoint control after DNA damage. Although 14-3-3 sigma is linked to p53-regulated cell cycle checkpoint control, detailed mechanisms of how cell cycle regulation occurs remain unclear. Decreased expression of 14-3-3 sigma was recently reported in several types of carcinomas, further suggesting that the negative regulatory role of 14-3-3 sigma in the cell cycle is compromised during tumorigenesis. However, this possible tumor-suppressive role of 14-3-3 sigma has not yet been characterized. Here, we studied the link between 14-3-3 sigma activities and p53 regulation. We found that 14-3-3 sigma interacted with p53 in response to the DNA-damaging agent adriamycin. Importantly, 14-3-3 sigma expression led to stabilized expression of p53. In studying the molecular mechanism of this increased stabilization of p53, we found that 14-3-3 sigma antagonized the biological functions of Mdm2 by blocking Mdm2-mediated p53 ubiquitination and nuclear export. In addition, we found that 14-3-3 sigma facilitated the oligomerization of p53 and enhanced p53's transcriptional activity. As a target gene of p53, 14-3-3 sigma appears to have a positive feedback effect on p53 activity. Significantly, we also showed that overexpression of 14-3-3 sigma inhibited oncogene-activated tumorigenicity in a tetracycline-regulated 14-3-3 sigma system. These results defined an important p53 regulatory loop and suggested that 14-3-3 sigma expression can be considered for therapeutic intervention in cancers.
mesh_terms: D048948:14-3-3 Proteins; D021581:Active Transport, Cell Nucleus; D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D000964:Antimetabolites, Antineoplastic / Q000494:pharmacology; D014408:Biomarkers, Tumor / Q000378:metabolism*; D015152:Blotting, Northern; D015153:Blotting, Western; D001973:Bromodeoxyuridine / Q000494:pharmacology; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism; D004249:DNA Damage; D015536:Down-Regulation; D004318:Doxycycline / Q000494:pharmacology; D005092:Exonucleases / Q000378:metabolism*; D005095:Exoribonucleases; D005260:Female; D017930:Genes, Reporter; D005982:Glutathione Transferase / Q000378:metabolism; D006801:Humans; D008156:Luciferases / Q000378:metabolism; D051379:Mice; D008819:Mice, Nude; D008856:Microscopy, Fluorescence; D008954:Models, Biological; D041681:NIH 3T3 Cells; D009363:Neoplasm Proteins / Q000378:metabolism*; D009369:Neoplasms / Q000378:metabolism*; D011233:Precipitin Tests; D011485:Protein Binding; D013997:Time Factors; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*; D025801:Ubiquitin / Q000378:metabolism
chemical_list: D048948:14-3-3 Proteins; D000900:Anti-Bacterial Agents; D000964:Antimetabolites, Antineoplastic; D014408:Biomarkers, Tumor; D009363:Neoplasm Proteins; D016159:Tumor Suppressor Protein p53; D025801:Ubiquitin; D008156:Luciferases; D005982:Glutathione Transferase; D005092:Exonucleases; D005095:Exoribonucleases; C413442:SFN protein, human; D001973:Bromodeoxyuridine; D004318:Doxycycline