The pro-apoptotic tumor suppressor gene PTEN (Phospatase and Tensin Homologue deleted from Chromosome 10) is a negative regulator of the PI-3 kinase/Akt dependent cell survival pathway. PTEN is located on chromosome 10q23 within a region that shows loss of heterozygosity in many human cancers, and PTEN gene function is lost in diverse cancers either by mutation of PTEN or deletion of chromosome 10q23. However, in several cancers such as non-small cell lung cancer and thyroid cancer, the PTEN gene is intact and wild type, but its expression is diminished. As haplo-insufficiency of PTEN is associated with tumorigenesis, understanding the mechanism(s) involved in epigenetic down-regulation of PTEN is of both clinical and fundamental significance. Recent studies have shown that the PTEN pseudo-gene but not wild type PTEN gene is methylated, indicating that DNA methylation is not a potential mechanism for silencing of the PTEN promoter leading to diminished PTEN gene expression. Our preliminary studies indicated that the anti-apoptotic transcriptional regulator NF-kappaB and oncogenic Ras, which are over-expressed and activated in lung cancer, down-regulate the expression of PTEN. Interestingly, oncogenic Ras up-regulates the expression of the transcription factor Egr-1, which by itself suppresses PTEN gene expression. The studies proposed here will address the mechanisms for down-regulation of PTEN gene expression that are functionally relevant; i.e., they result in elevated phospho-Akt levels and anti-apoptosis. We will determine the mechanisms of suppression of PTEN gene expression by NF-kappaB (Aim 1), and by oncogenic Ras (Aim 2) that confer apoptosis inhibition, tumor progression and chemo- or radiation-resistance. Because these studies will elucidate novel mechanisms of PTEN tumor suppressor gene regulation by pro-survival and oncogenic factors most commonly encountered in lung cancer, the findings may lead to the development of intervention strategies that can ablate the NF-kappaB or activated Ras-inducible anti-apoptotic pathways and thereby restore expression and the pro-apoptotic potential of PTEN.
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