Role of the mitogen-activated protein kinase signaling pathway in the regulation of human melanocytic antigen expression.
Heterogeneous expression of melanocytic antigens occurs frequently in melanomas and represents a potent barrier to immunotherapy. We previously showed that coordinated losses of several melanocytic antigens are generally attributable to down-regulation of antigen gene expression rather than irreversible mutation. Treatment of melanoma cells with mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) kinase (MEK) inhibitors blocks ERK activation and increases steady-state levels of mRNAs and corresponding protein expression for the melanocytic antigens Melan-A/MART-1, gp100, and tyrosinase. Although the degree of MEK inhibitor enhancement of antigen expression varied among different cell lines irrespective of their antigen expression status, all showed detectable responses. Notably, the antigen-enhancing effects of the MEK inhibitors could not be attributed to the master melanocytic regulator MITF-M. Because MAPK pathway activation via constitutively active mutant forms of BRAF is common in melanomas, correlation between BRAF function and antigen expression was investigated. No simple correlation of endogenous BRAF mutational status and antigen levels was observed, but transient overexpression of V600E BRAF increased ERK activation and reduced Melan-A/MART-1 levels in antigen-positive cell lines. These data indicate that whereas multiple factors may regulate antigen expression in melanomas, enhancement of MAPK signaling can act as a negative influence. Blocking such signaling with MEK inhibitors accordingly augments antigen levels, thereby enhancing Melan-A/MART-1-specific cytotoxic T-cell responses to antigen-negative cells following MEK inhibition treatment. Consequently, MAPK inhibition may assist targeting of melanomas for immunotherapy.
Kono
Michihiro
M
Department of Pathology, Massachusetts General Hospital, and Harvard Medical School, Boston, MA, USA.
Dunn
Ian S
IS
Durda
Paul J
PJ
Butera
David
D
Rose
Lenora B
LB
Haggerty
Timothy J
TJ
Benson
Elizabeth M
EM
Kurnick
James T
JT
D000951:Antigens, Neoplasm / Q000378:metabolism*; D002070:Butadienes / Q000494:pharmacology; D045744:Cell Line, Tumor; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D020935:MAP Kinase Signaling System; D058965:MART-1 Antigen; D008544:Melanocytes / Q000378:metabolism*; D008545:Melanoma / Q000378:metabolism*; D051739:Microphthalmia-Associated Transcription Factor / Q000502:physiology; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D009363:Neoplasm Proteins / Q000378:metabolism*; D009570:Nitriles / Q000494:pharmacology; D009930:Organic Chemicals / Q000494:pharmacology; D012150:Polymorphism, Restriction Fragment Length; D048493:Proto-Oncogene Proteins B-raf / Q000235:genetics / Q000378:metabolism; D013602:T-Lymphocytes, Cytotoxic / Q000502:physiology; D014158:Transcription, Genetic; D014162:Transfection
D000951:Antigens, Neoplasm; D002070:Butadienes; D004791:Enzyme Inhibitors; D058965:MART-1 Antigen; C548667:MLANA protein, human; D051739:Microphthalmia-Associated Transcription Factor; D009363:Neoplasm Proteins; D009570:Nitriles; D009930:Organic Chemicals; C466090:PD 98058; C113580:U 0126; C482119:BRAF protein, human; D048493:Proto-Oncogene Proteins B-raf; D020928:Mitogen-Activated Protein Kinases