PARP1 is overexpressed in nasopharyngeal carcinoma and its inhibition enhances radiotherapy

Nasopharyngeal carcinoma is a rare but highly invasive cancer. As options of agents for effectivecombination chemoradiotherapy for advanced nasopharyngeal carcinoma are limited, novel therapeutic approaches are desperately needed. The ubiquitin ligase CHFR is known to target PARP1 for degradation and is epigenetically inactivated in nasopharyngeal carcinoma. We present evidence that PARP1 protein is indeed overexpressed in nasopharyngeal carcinoma cells in comparison with immortalized normal nasopharyngeal epithelial cells. Tissue microarray analysis also indicated thatPARP1protein is significantly elevated in primary nasopharyngeal carcinoma tissues, with strong correlation with all stages of nasopharyngeal carcinoma development. We found that the PARP inhibitor AZD2281 (olaparib) increased DNA damage, cell-cycle arrest, and apoptosis in nasopharyngeal carcinoma cells challenged with ionizing radiation or temozolomide. Isobologram analysis confirmed that the cytotoxicity triggered by AZD2281 and DNAdamaging agents was synergistic. Finally, AZD2281 also enhanced the tumor-inhibitory effects of ionizing radiation in animal xenograft models. These observations implicate that PARP1 overexpression is an early event in nasopharyngeal carcinoma development and provide a molecular basis of using PARP inhibitors to potentiate treatment of nasopharyngeal carcinoma with radio- and chemotherapy. Mol Cancer Ther; 12(11); 2517-28. © 2013 AACR

Tumor suppressor Alpha B-crystallin (CRYAB) associates with the cadherin/catenin adherens junction and impairs NPC progression-associated properties

Alpha B-crystallin (CRYAB) maps within the nasopharyngeal carcinoma (NPC) tumor-suppressive critical region 11q22-23 and its downregulation is significantly associated with the progression of NPC. However, little is known about the functional impact of CRYAB on NPC progression. In this study we evaluated the NPC tumor-suppressive and progression-associated functions of CRYAB. Activation of CRYAB suppressed NPC tumor formation in nude mice. Overexpression of CRYAB affected NPC progression-associated phenotypes such as loss of cell adhesion, invasion, interaction with the tumor microenvironment, invasive protrusion formation in three dimensional Matrigel culture, as well as expression of epithelial-mesenchymal transition-associated markers. CRYAB mediates this ability to suppress cancer progression by inhibition of E-cadherin cytoplasmic internalization and maintenance of beta-catenin in the membrane that subsequently reduces the levels of expression of critical downstream targets such as cyclin-D1 and c-myc. Both ectopically expressed and recombinant CRYAB proteins were associated with endogenous E-cadherin and beta-catenin, and, thus, the cadherin/catenin adherens junction. The CRYAB alpha-crystallin core domain is responsible for the interaction of CRYAB with both E-cadherin and beta-catenin. Taken together, these results indicate that CRYAB functions to suppress NPC progression by associating with the cadherin/catenin adherens junction and modulating the beta-catenin function.link_to_subscribed_fulltex

LTBP-2 confers pleiotropic suppression and promotes dormancy in a growth factor permissive microenvironment in nasopharyngeal carcinoma

This study identified LTBP-2 as a pleiotropic tumor suppressor in nasopharyngeal carcinoma, which safeguards against critical malignant behaviors of tumor cells. LTBP-2 expression was significantly decreased or lost in up to 100% of NPC cell lines (7/7) and 80% of biopsies (24/30). Promoter hypermethylation was found to be involved in LTBP-2 silencing. Using a tetracycline-regulated inducible expression system, we unveiled functional roles of LTBP-2 in suppressing colony formation, anchorage-independent growth, cell migration, angiogenesis, VEGF secretion, and tumorigenicity. Three-dimensional culture studies suggested the involvement of LTBP-2 in maintenance of tumor cell dormancy in a growth factor favorable microenvironment. © 2012 Elsevier Ireland Ltd.link_to_subscribed_fulltex