Abstract 2478: Glycosylation of tid1 regulates galectin-7 ubiquitination and localization to suppress head and neck cancer metastasis
Authors: Chen Yu-Syuan 
Published: May 2015

Abstract
Background: Tid1, a DnaJ cochaperone protein mainly located in mitochondria, functions as a tumor suppressor in different types of solid tumors. Recently, we first demonstrate that Tid1 is negatively associated with cell migration, tumor status, and survival prognosis in head and neck squamous cell carcinoma (HNSCC) (J Pathol 2009; 219:347-55). As a cochaperone protein like Tid1, it should be instrumental to find the Tid1 client/interacting proteins, consequently, to understand the physiological function of those Tid1 client/interacting proteins as therapeutic targets for future HNSCC treatment.
Methods: First, we applied affinity chromatography and systemic proteomics analysis to identify galectin-7 as one of client/interacting proteins of Tid1. Subsequently, using the metastatic and/or non-metastatic cells determined tumorigenic properties of HNSCC with overexpression and/or knockdown of galectin-7 and/or Tid1. The nuclear and cytosolic subfractions were isolated to determine the role of Tid1 of galectin-7 nuclearization. We also attempted to correlate the expression of Tid1 and galectin-7 with tumor stage of HNSCC patient tissues by immunohistochemical assay. Finally, site-directed mutagenesis was applied to identify the novel N-link glycosylated sites of Tid1, by which to regulate the interaction and stability of galectin-7.
Results: We found metastatic cells expressed lower level of Tid1 and higher level of galectin-7 than non-metastatic cells. For in vitro tumorigenic analyses, we observed that overexpression of galectin-7 resulted in elevated migration, invasion and soft agar colony formation abilities in HNSCC. Inversely, co-overexpression of Tid1 reduced the expression of galectin-7, impaired the galectin-7 mediated migration, invasion and soft agar colony formation ability of HNSCC, and retarded nuclearization of galectin-7. Moreover, knockdown of galectin-7 reduced migration, invasion and soft agar colony formation ability of HNSCC metastatic cells. Further, we found that galectin-7 ubiquitination as revealed by antiubiquitin immunoblot analysis in immunoprecipitates. Finally, the negative relationship was between Tid1 and Galectin-7 expression in HNSCC clinical specimen. We found out that Tid1 interacts with galectin-7 through N-linked glycosylation. Tid1 mutants of N-link glycosylated sites restored the level and the tumorigenic function of galectin-7.
Conclusion: Our studies first pointed out that galectin-7 plays pivotal roles in HNSCC tumorigenesis. Notably, we identified galectin-7, which is the client/interacting protein of Tid1. We hypothesized that Tid1/ Hsp70 may regulate galectin-7 stability by ubiquitinylation. The molecular mechanism by which Tid1 negatively modulates the galectin-7 warrants further investigation.
Citation Format: Yu-Syuan Chen. Glycosylation of tid1 regulates galectin-7 ubiquitination and localization to suppress head and neck cancer metastasis. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2478. doi:10.1158/1538-7445.AM2014-2478