Targeting mutant (V600E) B-Raf in melanoma interrupts immunoediting of leukocyte functions and melanoma extravasation.
Polymorphonuclear neutrophils (PMN) facilitate melanoma cell extravasation under dynamic flow conditions by the binding of intercellular adhesion molecule-1 (ICAM-1) on melanoma cells to beta2 integrins on PMNs, which is mediated by endogenously produced chemokine interleukin 8 (IL-8) from the tumor microenvironment. However, little is known about the role of B-Raf, the most mutated gene in malignant melanomas, in this process. In this study, we investigated the functional importance of B-Raf in melanoma extravasation by using short interfering RNA to reduce expression/activity of mutant (V600E)B-Raf in melanoma. Results indicated that knockdown of mutant (V600E)B-Raf inhibited melanoma cell extravasation in vitro and subsequent lung metastasis development in vivo. Mechanistic studies showed that inhibition of (V600E)B-Raf significantly reduced the constitutive secretion of IL-8 from melanoma cells as well as the capacity of endogenous IL-8 production from the melanoma-PMN microenvironment. Furthermore, a reduction in ICAM-1 expression on melanoma cells was detected following mutant (V600E)B-Raf knockdown. Together, these results suggest that targeting mutant (V600E)B-Raf reduces melanoma cell extravasation by decreasing IL-8 production and interrupting ICAM-1-beta2 integrin binding of melanoma cells to the endothelium mediated by PMNs in the microcirculation, which provides a rationale and mechanistic basis for targeting mutant (V600E)B-Raf to inhibit melanoma extravasation and subsequent metastasis development.
Liang
Shile
S
Huck Institutes of the Life Sciences, The Pennsylvania State University, University Park, Pennsylvania 16802, USA.
Sharma
Arati
A
Peng
Hsin-Hsin
HH
Robertson
Gavin
G
Dong
Cheng
C
D000818:Animals; D045744:Cell Line, Tumor; D002465:Cell Movement / Q000502:physiology*; D024202:Electrophoretic Mobility Shift Assay; D004727:Endothelium / Q000378:metabolism; D006801:Humans; D018799:Intercellular Adhesion Molecule-1 / Q000378:metabolism; D016209:Interleukin-8 / Q000378:metabolism; D008175:Lung Neoplasms / Q000556:secondary; D008546:Melanoma, Experimental / Q000473:pathology*; D051379:Mice; D008819:Mice, Nude; D009154:Mutation; D009361:Neoplasm Invasiveness / Q000473:pathology*; D009368:Neoplasm Transplantation; D009504:Neutrophils / Q000378:metabolism*; D048493:Proto-Oncogene Proteins B-raf / Q000235:genetics / Q000378:metabolism*; D034741:RNA, Small Interfering
D016209:Interleukin-8; D034741:RNA, Small Interfering; D018799:Intercellular Adhesion Molecule-1; C482119:BRAF protein, human; D048493:Proto-Oncogene Proteins B-raf