Figure 7. Endothelial GRK2 levels influence tumor growth by altering pericyte recruitment and tumor microvasculature.

(A) Tumors implanted in mice with reduced endothelial expression of GRK2 exhibit higher growth rates. B16F10 melanoma cells were subcutaneously injected in mice and tumor size was monitored as described in Methods (n = 3–4 animals for each condition in 3 independent experiments). P values indicated in comparisons between WT and hemizygous mice and between hemizygous and Tie2Cre-Grk2^fl/– mice. (B and C) Higher occurrence of large and dilated vessels in tumors grown in Tie2Cre-Grk2^fl/– mice. Tumor sections were stained with the endothelial biotinylated ILB4 marker and hematoxylin counterstained. Vessel size was calculated as detailed in Methods. Distribution of vessel diameter in each condition is shown in C. (D and E) Reduced pericyte recruitment in tumors implanted in Tie2Cre-Grk2^fl/– mice. Sections of tumors were (D) stained with biotinylated ILB4 and anti-SMA antibodies or (E) double stained with fluorescein-ILB4 and anti-SMA antibodies to quantify the mural coverage as described in Methods. Data were expressed as a percentage of the total ILB4-positive area. (F) Tumors grown in Tie2Cre-Grk2^fl/– mice show increased macrophage density compared to those implanted in WT mice. The number of F4/80-positive cells in different sections covering the whole tumor mass is shown. Two distinct specimens were analyzed for each condition. Scale bar: 100 μm.