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HIF‐1α Is a Regulator of Galectin‐3 Expression in the Intervertebral Disc
Author(s) -
Zeng Yan,
Danielson Keith G,
Albert Todd J,
Shapiro Irving M,
Risbud Makarand V
Publication year - 2007
Publication title -
journal of bone and mineral research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.882
H-Index - 241
eISSN - 1523-4681
pISSN - 0884-0431
DOI - 10.1359/jbmr.070620
Subject(s) - regulator , intervertebral disc , galectin 3 , microbiology and biotechnology , galectin 1 , medicine , biology , anatomy , pathology , genetics , gene
Abstract The regulation of galectin‐3 expression in skeletal tissues is not completely understood. Our studies indicate that HIF‐1α regulates galectin‐3 expression by interacting with hypoxia regulatory elements in the promoter region. Finally, we show that galectin‐3 serves a prosurvival role in the intervertebral disc. Introduction: Earlier reports indicated that galectin‐3 (gal‐3) is highly expressed in the epiphyseal growth plate cartilage and the intervertebral disc. Because these skeletal tissues have a limited vascular supply and the cells reside in a low O 2 environment, we determined if the oxemic status modulates gal‐3 expression. Materials and Methods: Cells were cultured in normoxia (21% O 2 ) or hypoxia (2% O 2 ), and gal‐3 expression and promoter activity were evaluated. Interaction of hypoxia inducible factor (HIF)‐1α with the gal‐3 promoter was confirmed by gel shift and site‐directed mutagenesis. Results: There was minimal oxygen‐dependent change in HIF‐1α levels and no change in gal‐3 expression and promoter activity in nucleus pulposus cells. In contrast, hypoxia induced gal‐3 mRNA, protein, and promoter activity in HeLa cells and mouse embryonic fibroblasts (MEFs) from HIF‐1α wildtype but not HIF‐1–null mice. To evaluate the importance of HIF‐1 in regulation of gal‐3 expression, we overexpressed HIF‐1α or constitutively active‐HIF‐1α in null MEF. An increase in gal‐3 promoter activity was observed in both normoxia and hypoxia. Similarly, suppression of HIF‐1α in nucleus pulposus cells, and wildtype MEF, using siRNA and pharmacological inhibitors resulted in suppression of gal‐3 promoter activity and mRNA levels. Analysis of the gal‐3 promoter indicated that it contained two hypoxia response elements (HREs). Gel‐shift and chromatin immunoprecipitation analysis confirmed that there was binding of HIF‐1α to the gal‐3 HRE. Furthermore, site‐directed mutagenesis of HRE completely blocked hypoxic induction of gal‐3 promoter activity. In nucleus pulposus cells, suppression of gal‐3 expression promoted FasL‐mediated apoptosis. Conclusions: Together, these studies showed that gal‐3 is a HIF‐1–regulated lectin that plays an important role in nucleus pulposus cell survival.