Abstract 3064: HPP1 tumor suppression and JAK-STAT signaling

Abstract

Abstract Introduction: HPP1 is a putative tumor suppressor gene that is epigenetically silenced in various tumor types including colorectal cancer. We have previously reported that the ectopic expression of HPP1 results in the upregulation of STAT1, STAT2 and a number of interferon-inducible genes, and that activation of STAT1 is critical for HPP1's growth suppressive functions. We have sought to comprehensively evaluate alterations and the importance of the JAK-STAT signaling axis as they relate to HPP1 overexpression. Methods: Full-length HPP1 was amplified and cloned into the pcDNA3.1 expression vector which was then stably transfected into the HCT116 colon cancer cell line. Western Blot analyses were performed to assess both expression and activation for STAT1, STAT2, STAT3, JAK1, JAK2, JAK3 and TYK2 in HPP1 transfectants and empty vector controls. Functional STAT1 and STAT2 promoter binding were quantified using luciferase reporter plasmids containing ISRE-(Interferon Stimulated Regulatory Element) and GAS-(Gamma Activated Site) promoter elements. Results: The overexpression of HPP1 resulted in increased expression and activation of STAT1 and STAT2. Overexpression of HPP1 was associated with significant increases in both STAT1:STAT1 (p=0.007) and STAT1:STAT2 (p=0.036) binding, suggesting HPP1 mediates tumor suppression via association with Type II-like (gamma) and Type I-like (alpha) interferon pathways. Furthermore, additional corresponding dose-dependent inductions of STAT1 and STAT2 activation were achieved by treatment of HPP1 transfectants with interferon gamma and alpha. In contrast to STAT1 and 2, forced expression of HPP1 resulted in a downregulation of both STAT3 total expression and activation. HPP1 transfectants demonstrated increases in expression and activation of JAK1, JAK2 and JAK3, as well as a reduction in levels of TYK2 and phosphoTYK2. Conclusion: Activation of JAK1, 2 and 3 likely contribute to the upregulation and phosphorylation of STAT1 and STAT2 which in turn, result in the activation of Type I- and Type II-like interferon-inducible elements and their growth suppressive effects. Moreover, we demonstrate a reciprocal abrogation of the oncogenic STAT3 and its associated dominant kinase TYK2. HPP1 appears to mediate tumor suppression via modulation of JAK-STAT-interferon pathways. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3064.