Human RELMβ is a mitogenic factor in lung cells and induced in hypoxia

RELMβ (resistin-like molecule) represents the most related human homologue of mouse RELMα, also known as hypoxic-induced mitogenic factor (HIMF). In this study, we isolated RELMβ cDNA from human lung tissue and performed regulatory and functional expression studies. RELMβ mRNA was upregulated in hypoxia in human lung A549 cell line as well as primary cultured adventitial fibroblasts and smooth muscle cells (SMC) of pulmonary arteries. Upon transfection of a RELMβ encoding expression plasmid into these cells, we observed significant induction of proliferation particularly in SMC and A549 cells, which could be blocked by phosphatidyl-inositol 3-kinase (PI3K) inhibitors LY294002 and wortmannin. The results suggest that human RELMβ may contribute to hypoxic-induced pulmonary vascular remodeling processes or hypoxia related fibrotic lung disease.