Hypoxia influences vasculogenic mimicry channel formation and tumor invasion-related protein expression in melanoma

Background: Hypoxia can enhance tumor cell invasion and metastasis. The cause and the molecular mechanism are still not clear. Methods: In our study, mouse melanoma B16 cells were inoculated into mouse ischemic limbs and non-ischemic controls and the engrafted melanomas were subsequently observed. Vasculogenic mimicry channels in melanoma tumors of the two groups were counted and the expression of HIF-1 alpha, MMP-2, MMP-9 and VEGF was assessed by immunohistochemical staining. Formalin-fixed, paraffin-embedded tissues were used for immunohistochemical staining. Results: In the early stage of engrafted melanoma growth, the size of melanomas in ischemic limbs increased slower than in the controls. However, later there was no obvious difference in their size. Melanoma tumors in the ischemic group had more vasculogenic mimicry channels than those in the controls (P = 0.039). Similarly, the expression of HIF-1 alpha, MMP-2, MMP-9 and VEGF was higher in the ischemic group than in the non-ischemic controls (P = 0.024, 0.047, 0.007 and 0.025, respectively). There was a positive association in melanoma cells of the ischemic group between expression of HIF-1 alpha and VEGF, and also between MMP-9 and MMP-2. In the ischemic group, there was statistical significance for the correlation between HIF-1 alpha and VEGF expression (r = 0.456, P = 0.038). Furthermore, MMP-2 expression was positively correlated with MMP-9 and VEGF expression (r = 0.589 and 0.502, P = 0.008 and 0.024, respectively). Conclusions: Melanoma cells in a hypoxic microenvironment increased HIF-1 alpha expression and induced the formation of vasculogenic mimicry channels to acquire an adequate blood supply. On the other hand, the expression of MMP-2 and MMP-9 in tumor tissue increased to enhance the invasiveness. HIF-1 alpha, MMP-2 and MMP-9 may be associated with the failure of stop-flow perfusion in some patients with melanoma. (c) 2006 Elsevier Ireland Ltd. All rights reserved.