KDR and hemangioma: Anyhow, HIF-1 is initially activated, and its downstream pathway VEGF is in turn stimulated in the presence of hypoxia, then activating PI3K/Akt signaling pathway, finally promoting vascular proliferation and resulting in hemangioma occurrence via the regulation of mTOR and p70S6K, which forms an autocrine loop of VEGF signaling via activation of VEGFR2.