Department of Pathophysiology, Ruijin Hospital, Shanghai Jiao-Tong University School of Medicine, China.
Carcinogenesis. 2010 Aug;31(8):1367-75. doi: 10.1093/carcin/bgq116. Epub 2010 Jun 4.
The expression of galectin-1, one of the most important lectins participating in the malignant tumor development, has been shown to be regulated by hypoxia, but its exact mechanism remains elusive. Here, we find that ectopically expressed hypoxia-inducible factor (HIF) 1alpha protein, an oxygen-sensitive subunit of HIF-1 that is a master factor for cellular response to hypoxia, significantly increases galectin-1 expression in both messenger RNA and protein levels in all four colorectal cancer (CRC) cell lines tested. However, hypoxia-induced galectin-1 expression cannot be seen in sentrin/SUMO-specific protease 1 homozygous-null mouse embryonic fibroblasts that fail to accumulate HIF-1alpha protein. Furthermore, silence of HIF-1alpha or HIF-1beta expression by specific short hairpin RNAs (shRNAs) antagonizes hypoxia-induced galectin-1 expression. All these results propose that galectin-1 is a direct target of transcriptional factor HIF-1. Applying luciferase reporter assay and chromatin immunoprecipitation, we identify that two hypoxia-responsive elements located at -441 to -423 bp upstream to transcriptional start site of galectin-1 gene are essential for HIF-1-mediated galectin-1 expression. Finally, the knockdown of galectin-1 by its specific shRNA can significantly reduce hypoxia-induced invasion and migration of CRC cell line, and the ectopic expression of galectin-1 can remarkably restore invasion and migration abilities of HIF-1alpha-knocked SW620 cells, proposing that galectin-1 mediates the HIF-1-induced migration and invasion of CRC cells during hypoxia. Taken together, our results shed new light for understanding mechanism for hypoxia/HIF-1-mediated migration/invasion of CRC cells.
半乳糖凝集素-1（Galectin-1）是参与恶性肿瘤发展的最重要的凝集素之一，其表达受缺氧调节，但确切机制尚不清楚。在这里，我们发现，过表达的缺氧诱导因子（Hypoxia-inducible factor，HIF）1α蛋白，作为 HIF-1 的氧敏感亚基，是细胞对缺氧反应的主要调节因子，可显著增加所测试的四种结直肠癌细胞（CRC）系中 Galectin-1 的信使 RNA 和蛋白水平的表达。然而，在无法积累 HIF-1α蛋白的同源缺失型鼠胚胎成纤维细胞（sentrin/SUMO-specific protease 1 homozygous-null mouse embryonic fibroblasts）中，不能观察到缺氧诱导的 Galectin-1 表达。此外，通过特异性短发夹 RNA（short hairpin RNA，shRNA）沉默 HIF-1α或 HIF-1β的表达可拮抗缺氧诱导的 Galectin-1 表达。所有这些结果表明 Galectin-1 是转录因子 HIF-1 的直接靶标。通过荧光素酶报告基因检测和染色质免疫沉淀实验，我们鉴定出 Galectin-1 基因转录起始点上游-441 至-423bp 处的两个缺氧反应元件对于 HIF-1 介导的 Galectin-1 表达至关重要。最后，通过其特异性 shRNA 敲低 Galectin-1 可显著降低 CRC 细胞系缺氧诱导的侵袭和迁移，而过表达 Galectin-1 可显著恢复 HIF-1α敲除的 SW620 细胞的侵袭和迁移能力，提示 Galectin-1 介导了 HIF-1 诱导的 CRC 细胞在缺氧时的迁移和侵袭。总之，我们的研究结果为理解缺氧/HIF-1 介导的 CRC 细胞迁移/侵袭的机制提供了新的视角。
