Rac1 and Tumor Angiogenesis Figure 4. Genetic ablation of Rac1 in endothelial cells does not impair tumor growth or tumor angiogenesis. A. Western blot analysis of Rac1 flox/flox PDGFB-iCreER OHT-treated primary endothelial cell extracts showed that Rac1 was barely detectable (lane 3) when compared with Rac1 flox/flox OHT-treated (lane 1) or Rac1 flox/flox PDGFB-iCreER vehicle treated (lane 2) endothelial cell extracts (left panel). Western blots of extracts from non-endothelial cells, treated as described above, showed no differences in Rac1 expression (right panel). Hsc-70 provided loading controls. Bar graphs represent densitometric values relative to Hsc-70. N = 2 independent experiments. B. B16F0 tumor volume and angiogenesis (blood vessel density) from tumors grown in OHT-treated Rac1 flox/flox (1, white), or placebo- (2, grey) or OHT- (3, black) treated Rac1 flox/flox PDGFB-iCreER mice. Left bar graph shows mean tumor volume in mm3 (+ s.e.m) for 10-day-old tumors. No significant differences in tumor size were observed between groups. N = 6–7 animals per group. Right bar graph shows mean number of PECAM-1 positive vessels per tumor area per mm2 (+ s.e.m.) for 10-day-old tumors. No significant differences in microvessel density were observed between groups. N = 4 animals per group. C. B16F0 tumor volume and angiogenesis (blood vessel density) from tumors grown in OHT-treated Rac1 flox/flox PDGFB-iCreER animals. Tumors were PLoS ONE | www.plosone.org 6 March 2010 | Volume 5 | Issue 3 | e9766