Faculty Bibliography

Little is known about the cellular mechanisms contributing to the development and chemoresistance of malignant mesothelioma (MM), an aggressive asbestos-associated tumor. A human mesothelial cell line (LP9/TERT-1) and isolated human pleural mesothelial cells showed rapid and protracted asbestos-induced cAMP response element binding protein (CREB1) phosphorylation, which was inhibited in LP9/TERT-1 cells by small molecule inhibitors of epidermal growth factor receptor phosphorylation and protein kinase A. Asbestos increased expression of several CREB target genes (c-FOS, EGR-1, MKP1, BCL2, and MMP13) and apoptosis, which was enhanced using small interfering CREB. Human MM tissue arrays showed elevated endogenous levels of phosphorylated nuclear CREB1 as compared with reactive mesothelial hyperplasias and normal lung tissue. Significantly increased phosphorylated CREB1 and mRNA levels of BCL2, c-FOS, MMP9, and MMP13 were also observed in MM cells in vitro, which were further augmented after addition of Doxorubicin (Dox). Small interfering CREB inhibited migration of MMs, increased apoptosis by Dox, and decreased BCL2 and BCL-xL expression, suggesting a role for these molecules in CREB-induced MM survival. These data indicate that CREB1 and its target genes are up-regulated in asbestos-exposed human mesothelial cells through an epidermal growth factor receptor/protein kinase A pathway. Since activated CREB1 also is increased endogenously in human MM and modifies migration and resistance to Dox-induced apoptosis, inhibition of CREB1 may be a new strategy for MM therapy

BACKGROUND: FUS1/TUSC2 is a novel tumor suppressor located in the critical 3p21.3 chromosomal region frequently deleted in multiple cancers. We previously showed that Tusc2-deficient mice display a complex immuno-inflammatory phenotype with a predisposition to cancer. The goal of this study was to analyze possible involvement of TUSC2 in malignant pleural mesothelioma (MPM) - an aggressive inflammatory cancer associated with exposure to asbestos. METHODS: TUSC2 insufficiency in clinical specimens of MPM was assessed via RT-PCR (mRNA level), Representational Oligonucleotide Microarray Analysis (DNA level), and immunohistochemical evaluation (protein level). A possible link between TUSC2 expression and exposure to asbestos was studied using asbestos-treated mesothelial cells and ROS (reactive oxygen species) scavengers. Transcripional effects of TUSC2 in MPM were assessed through expression array analysis of TUSC2-transfected MPM cells. RESULTS: Expression of TUSC2 was downregulated in approximately 84% of MM specimens while loss of TUSC2-containing 3p21.3 region observed in approximately 36% of MPMs including stage 1 tumors. Exposure to asbestos led to a transcriptional suppression of TUSC2, which we found to be ROS-dependent. Expression array studies showed that TUSC2 activates transcription of multiple genes with tumor suppressor properties and down-regulates pro-tumorigenic genes, thus supporting its role as a tumor suppressor. In agreement with our knockout model, TUSC2 up-regulated IL-15 and also modulated more than 40 other genes (approximately 20% of total TUSC2-affected genes) associated with immune system. Among these genes, we identified CD24 and CD274, key immunoreceptors that regulate immunogenic T and B cells and play important roles in systemic autoimmune diseases. Finally, clinical significance of TUSC2 transcriptional effects was validated on the expression array data produced previously on clinical specimens of MPM. In this analysis, 42 TUSC2 targets proved to be concordantly modulated in MM serving as disease discriminators. CONCLUSION: Our data support immuno-therapeutic potential of TUSC2, define its targets, and underscore its importance as a transcriptional stimulator of anti-tumorigenic pathways