Regulation of lysyl oxidase expression in THP-1 cell-derived M2-like macrophages.

Lysyl oxidase (LOX) is a copper-containing enzyme and its overexpression in tumor tissues promote tumor metastasis through the crosslinking of extracellular matrix. Our previous report demonstrated that LOX expression is significantly increased in human leukemic THP-1 cell-derived M2-like macrophages, and histone modification plays a key role in its induction. However, the rigorous mechanism of LOX regulation remains unclear. In this study, we investigated the role of functional transcription factors, hypoxia-inducible factor 1α (HIF1α), signal transducer and activator of transcription 3 (STAT3) and forkhead box O1 (FOXO1) in LOX regulation in M2-like macrophages. HIF1α expression was significantly increased in M2-like macrophages, and HIF1α inhibitor, TX402, suppressed LOX induction. The significant STAT3 activation was also observed in M2-like macrophages. Additionally, LOX induction was canceled in the presence of STAT3 inhibitor, S3I-201, suggesting that HIF1α and STAT3 pathways play a critical role in LOX induction. On the other hand, our ChIP results clearly indicated that the enrichment of FOXO1 within the lox promoter region was dramatically decreased in M2-like macrophages. In this context, knockdown of FOXO1 further enhanced LOX induction. LOX induction and HIF1α binding to the lox promoter region were suppressed in FOXO1-overexpressed cells, suggesting that the FOXO1 binding to the lox promoter region counteracted HIF1α binding to that region. Overall, the present data suggested that both of HIF1α and STAT3 were required for LOX induction in M2-like macrophages, and loss of FOXO1 within the lox promoter region facilitated HIF1α binding to that region which promoted LOX induction.

Lysyl oxidase expression is regulated by the H3K27 demethylase Jmjd3 in tumor-associated M2-like macrophages.

Copper is one of the essential micronutrients, and copper-containing enzymes contribute to crucial functions in the body. Lysyl oxidase is a copper-containing enzyme that remodels the extracellular matrix by cross-linking collagen and elastin. The overexpression of lysyl oxidase was recently shown to promote tumor metastasis. M2-like macrophages were also found to significantly accumulate in the tumor microenvironment, and correlated with a poor patient's outcome. We speculate that M2-like macrophages promote tumor progression via lysyl oxidase expression. Epigenetics, a mitotically heritable change in gene expression without any change in DNA sequencing, is also associated with tumor progression. However, the relationship between lysyl oxidase expression in M2-like macrophages and epigenetics remains unclear. Lysyl oxidase expression was significantly induced in human leukemic THP-1 cell-derived M2-like macrophages. Furthermore, the level of histone H3 tri-methylation at lysine 27 was decreased, and a pre-treatment with a H3K27 demethylase inhibitor notably suppressed lysyl oxidase expression in M2-like macrophages. Lysyl oxidase derived from M2-like macrophages also enhanced breast cancer cell migration, and this was suppressed by a H3K27 demethylase inhibitor. The present results suggest the mechanism of lysyl oxidase expression in M2-like macrophages as an aspect of epigenetics, particularly histone methylation.