Runx3 inhibits endothelial progenitor cell differentiation and function via suppression of HIF-1α activity

Endothelial progenitor cells (EPCs) are bone marrow (BM)-derived progenitor cells that can differentiate into mature endothelial cells, contributing to vasculogenesis in the blood vessel formation process. Runt-related transcription factor 3 (RUNX3) belongs to the Runt domain family and is required for the differentiation of specific immune cells and neurons. The tumor suppressive role of RUNX3, via the induction of apoptosis and cell cycle arrest in a variety of cancers, and its deletion or frequent silencing by epigenetic mechanisms have been studied extensively; however, its role in the differentiation of EPCs is yet to be investigated. Therefore, in the present study, adult BM-derived hematopoietic stem cells (HSCs) were isolated from Runx3 heterozygous (Rx3(+/-)) or wild-type (WT) mice. The differentiation of EPCs from the BM-derived HSCs of Rx3(+/-) mice was found to be significantly increased compared with those of the WT mice, as determined by the number of small or large colony-forming units. The migration and tube formation abilities of Rx3(+/-) EPCs were also observed to be significantly increased compared with those of WT EPCs. Furthermore, the number of circulating EPCs, defined as CD34(+)/vascular endothelial growth factor receptor 2 (VEGFR2)(+) cells, was also significantly increased in Rx3(+/-) mice. Hypoxia-inducible factor (HIF)-1 alpha was upregulated in Rx3(+/-) EPCs compared with WT EPCs, even under normoxic conditions. Furthermore, in a hindlimb ischemic mouse models, the recovery of blood flow was observed to be highly stimulated in Rx3(+/-) mice compared with WT mice. Also, in a Lewis lung carcinoma cell allograft model, the tumor size in Rx3(+/-) mice was significantly larger than that in WT mice, and the EPC cell population (CD34(+)/VEGFR2(+) cells) recruited to the tumor was greater in the Rx3(+/-) mice compared with the WT mice. In conclusion, the present study revealed that Runx3 inhibits vasculogenesis via the inhibition of EPC differentiation and functions via the suppression of HIF-1 alpha activity.