15-hydroxyprostaglandin dehydrogenase (15-PGDH) is a target gene of the candidate tumor suppressor, HNF3β in lung cancers Free

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Hepatocyte nuclear factor 3beta (HNF3beta), also named Foxa2, belongs to the forkhead family of transcription factors. This transcription factor is essential in foregut development and is known to be involved in the regulation of several lung-specific genes. Previously we showed that HNF3beta expression was regulated by C/EBP alpha, a tumor suppressor in lung cancers, and that its expression led to substantial cell growth reduction explained by G2-M growth arrest and cell apoptosis. HNF3beta expression is lost in about half of all non-small cell lung cancers, partly due to promoter methylation and HNF3beta is a candidate tumor suppressor in lung cancer. In the present study, we utilized a doxycycline-inducible stable cell line, H358-HNF3beta (tet-off), to identify the downstream targets through which HNF3beta regulates lung cancer cell growth. Gene chip assays performed at different times of HNF3beta induction identified a number of downstream targets of HNF3beta and several of those were further confirmed by TaqMan analysis. These studies strongly suggested that 15-PGDH is one of the major genes induced by HNF3beta expression. PGDH is a critical metabolic enzyme of proliferative prostaglandin and acts as an antagonist to COX2 in colon cancers and is a bona fide tumor suppressor. Its regulation by HNF3beta was confirmed by quantitative RT-PCR, where 15-PGDH mRNA level was increased as early as 12 hours upon HNF3beta induction and a maximum 15 fold increase was seen at 96 hours. Western blotting corroborated up-regulation of 15-PGDH protein in response to the induction of HNF3beta. Luciferase reporter assays demonstrated a significant increase in 15-PGDH promoter activity upon the induction of HNF3beta. Further studies using chromatin immunoprecipitation assays followed by quantitative PCRs demonstrated direct binding between HNF3beta and two predicted HNF3beta binding sites of the promoter of the 15-PGDH gene with the degree of binding closely dependent on HNF3beta protein levels. In summary, we identified downstream transcriptional changes as a result of HNF3beta induction and demonstrate that 15-PGDH is a direct downstream effector of HNF3beta. Current studies being conducted focus on the correlation between the expression levels of HNF3beta and 15-PGDH in other lung cancer cell lines as well as in normal and tumor human lung epithelia. Functional properties of 15-PGDH are also being explored to identify the role of this effector in lung cancers.