Abstract A26: Tumor-suppressive LTBP2 is associated with NF-kB signaling pathway regulation in nasopharyngeal carcinoma
Authors: Kan Rebecca , Cheung Arthur Kwok Leung , Lung Maria Li 
Published: August 2014

In our previous study, in vivo and in vitro assays led to the discovery of Latent Transforming Growth Factor-b Binding Protein 2 (LTBP2), in nasopharyngeal carcinoma (NPC). LTBP2, mapping to chromosome 14q24, was confirmed to have high allelic loss in NPC tumors and showed its potential as a candidate tumor suppressor gene (TSG) in NPC. The LTBP2 gene encodes a 5.5kb secreted extracellular matrix protein. Our initial studies suggested that LTBP2 was significantly down-regulated in all seven NPC cell lines and in more than 85% (n=30) of patient biopsies. Further analysis of LTBP2-stable transfectants revealed its multi-functional roles in the maintenance of tumor cell dormancy in a growth factor favorable microenvironment.

In this current study, by utilizing a lentiviral infection system, LTBP2 was transduced into NPC cell lines, HONE1 and HK1. LTBP2-transduced cells displayed reduced colony formation ability, cell migration, in vivo tumor formation, and angiogenesis. The intrinsic biochemical pathway(s) implicated by LTBP2 was then scrutinized, revealing its relationship with the signal transduction pathway of the NF-kB protein. Western blotting analysis showed that re-expression of LTBP2 attenuated activities of NF-kB signaling pathway members and inhibited various NF-kB signaling-associated pro-tumorigenic downstream proteins. Real-time PCR was used to validate the transcription levels of NF-kB signaling-associated downstream targets, including angiogenesis markers, cell adhesion molecules, pro-tumorigenic proteins, proto-oncogenes, transcription factors, and repressors. NF-kB is recognized as a key pleiotropic transcriptional regulator, involved in diverse biological processes such as immune responses, cellular development, proliferation and survival, programmed cell death, cell adhesion, and tissue remodeling. Its expression is tightly coordinated by internal and external stimuli.

To further determine the critical functional domains of LTBP2, truncated gene constructs were cloned into the lentiviral vector and subsequently transduced into NPC cell lines. We have successfully expressed the LTBP2 protein deletion constructs in the NPC system. Colony formation assay was also performed to identify the functional regions or domains that are crucial for LTBP2 function.

In conclusion, LTBP2 appears to be a critical extracellular glycoprotein regulator in the normal cell microenvironment. Hence, its loss may lead to tumorigenesis. Acknowledgements: This work was supported by the Research Grants Council Area of Excellence scheme of the Hong Kong Special Administrative Region, People's Republic of China (AoE/M-06/08, to M.L.L.)

Citation Format: Rebecca Kan, Arthur Kwok Leung Cheung, Maria Li Lung. Tumor-suppressive LTBP2 is associated with NF-kB signaling pathway regulation in nasopharyngeal carcinoma. [abstract]. In: Proceedings of the Third AACR International Conference on Frontiers in Basic Cancer Research; Sep 18-22, 2013; National Harbor, MD. Philadelphia (PA): AACR; Cancer Res 2013;73(19 Suppl):Abstract nr A26.