Context dependent role of the CD36--thrombospondin--histidine-rich glycoprotein axis in tumor angiogenesis and growth.
The angiogenic switch is a promising therapeutic target in cancer. Work by our laboratory and others has described an important endogenous anti-angiogenic pathway mediated by interactions of CD36, a receptor on microvascular endothelial cells, with proteins containing thrombospondin (TSP) type I repeat domains (TSR). Recent studies revealed that circulating Histidine Rich Glycoprotein (HRG) inhibits the anti-angiogenic potential of the CD36-TSR pathway by functioning as a decoy receptor that binds and sequesters TSR proteins. As tumors of different origin display variable expression profiles of numerous targets, we hypothesized that the TSP-CD36-HRG axis regulates vascularization and growth in the tumor microenvironment in a context, or tumor type, dependent manner. Growth of Lewis Lung Carcinoma (LL2) and B16F1 Melanoma tumor cell implants in syngeneic wild type (WT), hrg, or cd36 null mice were used as a model to interrogate this signaling axis. LL2 tumor volumes were greater in cd36 null mice and smaller in hrg null mice compared to WT. Immunofluorescent staining showed increased vascularity in cd36 null vs. WT and WT vs. hrg null mice. No differences in tumor growth or vascularity were observed with B16F1 implants, consistent with lack of expression of TSP-1 in B16F1 cells. When TSR expression was induced in B16F1 cells by cDNA transfection, tumor growth and vascularity were similar to that seen with LL2 cells. These data show a role for CD36-mediated anti-angiogenic activity in the tumor microenvironment when TSR proteins are available and demonstrate that HRG modulates this activity. Further, they suggest a mechanism by which tumor microenvironments may regulate sensitivity to TSR containing proteins.
Department of Biological, Geological and Environmental Sciences, Cleveland State University, Cleveland, Ohio, United States of America.
James Scott
JS
Hale
Meizhang
M
Li
Maksim
M
Sinyuk
Willi
W
Jahnen-Dechent
Justin Durla
JD
Lathia
Roy Lee
RL
Silverstein
D000818:Animals; D018955:CD36 Antigens / Q000172:deficiency / Q000235:genetics*; D018827:Carcinoma, Lewis Lung / Q000098:blood supply* / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D045744:Cell Line, Tumor; D042783:Endothelial Cells / Q000378:metabolism / Q000473:pathology; D015972:Gene Expression Regulation, Neoplastic; D008297:Male; D008546:Melanoma, Experimental / Q000098:blood supply* / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D051379:Mice; D018345:Mice, Knockout; D009389:Neovascularization, Pathologic; D009928:Organ Specificity; D011485:Protein Binding; D011506:Proteins / Q000235:genetics* / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics; D015398:Signal Transduction; D012878:Skin Neoplasms / Q000098:blood supply* / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D019700:Thrombospondin 1 / Q000235:genetics* / Q000378:metabolism; D047368:Tumor Burden / Q000235:genetics; D059016:Tumor Microenvironment / Q000235:genetics; D000099053:Histidine-Rich Glycoprotein
D018955:CD36 Antigens; D011506:Proteins; D034741:RNA, Small Interfering; D019700:Thrombospondin 1; D000099053:Histidine-Rich Glycoprotein