[18], [19] To our knowledge, the effects of hypoxia on ARG expression in cancer tissues or fibroblasts have not been demonstrated previously. Our study together with the study that hypoxia induced expression of ARG2 but not ARG1 in PASMCs suggests that ARG2 is the hypoxia-inducible isoform. [17] It is consistent with our findings that accumulation of HIF-1α was found in CAFs under hypoxic conditions and also that the 5' flanking region of the first exon of the ARG2 gene has potential binding sites for HIF-1. Here, ARG1 is linked to cancer.