**5.5.1 Regulation of VEGF and hypoxia inducible factor-1 (HIF1)**

It has been reported that hypoxia increases the expression and activity of Cdc42, Rac1 and RhoA in renal cell carcinoma cell lines and a human microvascular endothelial cell line (Turcotte, Desrosiers et al. 2003). This study demonstrated that reactive oxygen species (ROS) are responsible for the upregulation of Rho proteins and that RhoA is required for the accumulation of HIF-1α (Turcotte, Desrosiers et al. 2003), a transcription factor induced by hypoxia that plays important roles in the process of angiogenesis by inducing the transcription of crucial mediators, including VEGF, PDGFβ and Ang-2 (Gleadle and Ratcliffe 1998). In contrast, Rac1 is shown to be involved in hypoxia-induced PI3K activation of HIF-1α through a different mechanism (Hirota and Semenza 2001). Hypoxiainduced expression of Rac1 also contributes to the upregulation of HIF-1α and, subsequently, VEGF in gastric and hepatocellular cancer cells (Xue, Bi et al. 2004). VEGF has been reported to increase RhoA activity and localization to the cell membrane, and the RhoA /ROCK pathway has been implicated in the VEGF-mediated angiogenesis (van Nieuw Amerongen, Koolwijk et al. 2003). In addition, RhoA activation also increases tyrosine phosphorylation of the primary VEGF receptor, VEGFR-2 (Gingras, Lamy et al. 2000).

Overexpression of RhoC in human mammary epithelial cells (HME) and a highly aggressive breast cancer cell line, SUM-149, increases VEGF expression (van Golen, Wu et al. 2000). Similar finding were found in the MCF10A cells (Wu, Wu et al. 2004), further suggesting that RhoC plays a role in, further suggesting that RhoC plays a role in increasing VEGF in mammary neoplasis.
