Tumor and Stem Cell Biology Cell Cycle Regulator ING4 Is a Suppressor of Melanoma Angiogenesis That Is Regulated by the Metastasis Suppressor BRMS1

ING4 has been previously shown to play important roles in regulating apoptosis, cell cycle progress, cell migration, and invasion. In this study, we investigated the impact of ING4 on melanoma angiogenesis. ING4 overexpression strongly suppressed the growth of human umbilical vein endothelial cells (HUVEC) and their ability to form tubular structure in vitro. We also found that ING4 inhibits interleukin-6 (IL-6) at both mRNA and protein levels through suppressing NF-kB activity. Knockdown of endogenous ING4 resulted in enhanced HUVEC growth and IL-6 expression. Our in vivo studies using nude mice confirmed that ING4 inhibited blood vessel formation and the recruitment of CD31-positive cells in matrigel plugs. Furthermore, we found that expression of ING4 was induced by BRMS1, a metastasis suppressor that inhibits melanoma angiogenesis through inhibiting NF-kB activity and IL-6 level as well. Further experiments showed that ING4 knockdown abrogated the suppressive effect of BRMS1 on HUVEC growth, whereas ING4 overexpression inhibited BRMS1 knockdown-induced angiogenesis, indicating that ING4 is a downstream target of BRMS1 in regulating tumor angiogenesis. Collectively, our findings indicate that ING4 is induced by BRMS1 and that it inhibits melanoma angiogenesis by suppressing NF-kB activity and IL-6 expression. Restoration of ING4 function offers a potential new strategy for the treatment of human melanoma. Cancer Res; 70(24); 10445–53. 2010 AACR.