The role of Lysine-specific demethylase 1 as a regulator of Hypoxia-inducible factor-1α in Tumor Angiogenesis

Abstract

The Lysine-Specific Demethylase 1 (LSD1/KDM1A), which has been shown to demethylate histone H3 on lysine 4 (H3K4), lysine 9 (H3K9) and several non-histone proteins, plays an important role in the epigenetic regulation of transcription and modulation of protein function. LSD1 is overexpressed in various cancers, but its biological significance in tumor development has not been fully elucidated. In addition, its role in breast cancer progression has been controversial. In this study, we investigated the effect of LSD1 on tumor angiogenesis in human breast cancer and found that LSD1 leads to increase the Hypoxia-Inducible Factor-1α (HIF-1α) and its target Vascular Endothelial Growth Factor (VEGF), a key angiogenic factor, expression. LSD1 enhanced the HIF-1α protein stability via the Von Hippel-Lindau protein (VHL)-dependent pathway. Knockdown of LSD1 using short hairpin RNA (shRNA) induced HIF-1α hydroxylation and the interaction between HIF-1α and VHL, thereby promoting VHL-mediated HIF-1α protein degradation. Mechanistically, LSD1 overexpression suppressed HIF-1α ubiquitination through the repression of interaction between HIF-1α and VHL mediated by decreasing HIF-1α hydroxylation levels. LSD1-induced HIF-1α expression was not affected by the treatment of pargyline, a monoamine oxidase inhibitor, indicating that the demethylase activity of LSD1 is not involved in regulation of HIF-1α expression. We also found that LSD1 modulates HIF-1α-mediated VEGF transcription via recruiting HIF-1α/CBP complex to the VEGF promoter during both normoxia and hypoxia. Furthermore, LSD1 enhanced tumor angiogenesis both in vitro and in vivo. Overexpression of LSD1 increased in vitro tube formation in human umbilical endothelial cells (HUVECs). LSD1 deficient xenograft tumors showed decreased tumor volume, microvessel density and HIF-1α expression levels. Taken together, these observations provided that LSD1 may be a novel regulator of HIF-1α protein and its target VEGF expressions mediated by VHL-dependent pathway, supporting an pro-oncogenic role of LSD1 as an inducer of tumor angiogenesis in human breast cancer.