Although constitutively activated NF-kB, attenuated TGFb signaling, and TP53 mutations frequently co-occur in human cancers, how these pathways interact and together contribute to malignancy and their potential as targets for therapy and prevention are an important problem. We previously found an association between overexpression of NF-kB related genes, altered expression of TGFb receptor (TBR) subunits and downstream targets in head and neck squamous cell carcinoma (HNSCC). During the past year we reported that TGFbeta receptor I/ phosphastase tensin (Tgfbr1/Pten) are frequently decreased in HNSCC, and conditional double knockout mice for these genes develop HNSCC that exhibit increased PI3K-Akt pathway and NF-kappaB/REL activation (Bian, Oncogene, 2012). Subsequent studies demonstrate the potential of PI3K-mTOR inhibitor for prevention of tumor development in these Tgfbr1/Pten dko mice and therapy of human xenograft bearing mice (Herzog, Bian et al., submitted). We found that PI3K-mTOR antagonist inhibited downstream progrowth signaling, reactivated tumor suppressor TP5, and sensitized tumors to cytotoxic chemotherapy and radiation. As co-recipients of an NIH Director's Bench to Bedside Award in collaboration with NIDCR investigators, we have initiated a pilot clinical study of neoadjuvant mTOR inhibitor rapamycin in patients with advanced HNSCC (NIH protocol 10-D-180). Heat Shock Protein 90 inhibitors target many oncoproteins in the signal network we have shown is co-activated in HNSCC. In collaborative studies, we reported that HSP90 inhibitors target overexpressed Epidermal growth factor receptor, downstream signaling, and strongly inhibits human HNSCC xenografts (Ahsan et al., Neoplasia, 2012). Another HSP90 inhibitor in phase I studies at NIH demonstrated inhibition of oncogenic signal and transcription factors and reactivation of wild type p53 in human tumor xenografts (Friedman et al., submitted). Inflammation and inflammatory signaling is implicated in promoting cancer development, including human head and neck squamous cell carcinomas (HNSCC). How inflammatory signals can inhibit cell growth arrest and apoptosis while promoting many genes involved in migration, angiogenesis, and metastasis is unclear. Inflammatory cytokine Tumor Necrosis Factor-alpha (TNF-alpha) induces nuclear translocation of NF-kB/REL transcription factors containing REL-A or c-REL, which mediate resistance to its cytotoxic effects and cell survival. REL-A induces pro-survival genes, but the distinctive functional role of c-REL is unclear. We recently collaborated with King, Weinberg and colleagues in the FDA, demonstrating that c-REL forms a novel nuclear complex with the p53 homologue DeltaNp63alpha in HNSCC (King K et al., Cancer Res, 2008). The TP53 family includes TP53 and TAp73, which can induce apoptosis, while deltaNp63alpha can inhibit their function and activate other genes. Examination of c-REL and TP53 family protein expression in human HNSCC reveals nuclear co-localization of c-REL and dNp63, while nuclear expression of pro-apoptotic family members p73 and TP53 is attenuated in a majority of tumors and cell lines. Interestingly, nuclear c-REL, dNp63, TAp73 and TP53 is observed in a subset of HNSCC cell lines with mutations of TP53 cultured in the absence of TNF-a. Addition of TNF-a enhanced c-REL nuclear interaction with dNp63a, displacing TAp73 from the nucleus and promoters of the key growth arrest and apoptotic genes p21CIP1/WAF1, NOXA and PUMA. Conversely, siRNA depletion of constitutive c-REL enhanced TAp73 promoter binding and expression of these genes, and inhibited cell proliferation and survival of cells containing mutant TP53. Thus, constitutive and TNF-a-induced c-REL/dNp63a represses TAp73 target pro-apoptotic genes in HNSCC. This novel cross-talk involving c-REL and the TP53 family provides a distinctive mechanism whereby inflammatory cytokines such as TNF-a and NF-kB family member cREL can dysregulate the compensatory role of TAp73 in growth arrest and apoptosis of cancer cells with mutant TP53 (Lu et al, Cancer Res, 2011). We hypothesized that dNp63 may have a potentially broader role in regulating NF-kB related as well as p53/p63/p73 target genes that promote cell proliferation, survival, migration, inflammation and angiogenesis in cancer. We found that deltaNp63, is often overexpressed with mutant TP53 and regulates a broad gene program implicated in HNSCC. This gene program substantially overlaps with the NF-kappaB transcriptome involved in cell growth, survival, inflammation and adhesion. This regulation includes a novel interaction where deltaNp63 complexes with NF-kappaB family member, cRel, to coordinately bind to p63 or p65/cRel sites of target gene promoters. Overexpression of deltaNp63 or TNF-alpha activates IL-8 reporter activity via a p65/cRel site in the proximal IL-8 promoter. Consistent with this diverse gene program, modulation of deltaNp63 significantly altered the HNSCC malignant phenotype. Our studies reveal a novel link between TP53 and NF-kappaB pathways, through a newly identified transcriptional mechanism via deltaNp63/cRel complex. This complex and its regulated downstream genes could serve as novel biomarkers and therapeutic targets in tumors with defective TP53 (Yang et al, Cancer Res, 2011).Together, these findings suggest signal regulation coordinating NF-kB, p63 and p73 interactions and function may be important in pathogenesis and as targets for prevention and therapy.
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