Melanoma cells exhibit variable signal transducer and activator of transcription 1 phosphorylation and a reduced response to IFN-alpha compared with immune effector cells.
OBJECTIVE
IFN-alpha is administered to melanoma patients and its endogenous production is essential for immune-mediated tumor recognition. We hypothesized that a reduced capacity for signal transducer and activator of transcription (STAT) 1 activation allows melanoma cells to evade the direct actions of IFN-alpha.


METHODS
Tyr(701)-phosphorylated STAT1 (P-STAT1) was measured by flow cytometry in IFN-alpha-stimulated human melanoma cell lines, melanoma cells derived from patient tumors, and peripheral blood mononuclear cells (PBMC). Expression of other Janus-activated kinase (Jak)-STAT intermediates (STAT1, STAT2, Jak1, tyrosine kinase 2, IFN-alpha receptor, STAT3, and STAT5) was evaluated by flow cytometry, immunoblot, or immunohistochemistry.


RESULTS
Significant variability in P-STAT1 was observed in human melanoma cell lines following IFN-alpha treatment (P < 0.05) and IFN-alpha-induced P-STAT1 correlated with the antiproliferative effects of IFN-alpha (P = 0.042). Reduced formation of P-STAT1 was not explained by loss of Jak-STAT proteins or enhanced STAT5 signaling as reported previously. Basal levels of P-STAT3 were inversely correlated with IFN-alpha-induced P-STAT1 in cell lines (P = 0.013). IFN-alpha-induced formation of P-STAT1 was also variable in melanoma cells derived from patient tumors; however, no relationship between P-STAT3 and IFN-alpha-induced P-STAT1 was evident. Because IFN-alpha acts on both tumor and immune cells, we examined the ability of IFN-alpha to induce P-STAT1 in patient-derived melanoma cells and PBMCs. IFN-alpha induced significantly lower levels of P-STAT1 in melanoma cells compared with matched PBMCs (P = 0.046). Melanoma cells and human melanocytes required 10-fold higher IFN-alpha doses to exert P-STAT1 levels comparable with PBMCs.


CONCLUSIONS
Melanoma cells are variable in their IFN-alpha responsiveness, and cells of the melanocytic lineage exhibit a lower capacity for IFN-alpha-induced Jak-STAT signaling compared with immune cells.
Lesinski
Gregory B
GB
Human Cancer Genetics Program, Department of Molecular Virology, Immunology and Medical Genetics, The Ohio State University, Columbus, Ohio 43210, USA.
Trefry
John
J
Brasdovich
Melanie
M
Kondadasula
Sri Vidya
SV
Sackey
Korkor
K
Zimmerer
Jason M
JM
Chaudhury
Abhik Ray
AR
Yu
Lianbo
L
Zhang
Xiaoli
X
Crespin
Tim R
TR
Walker
Michael J
MJ
Carson
William E
WE
D000818:Animals; D006801:Humans; D016898:Interferon-alpha / Q000494:pharmacology*; D053613:Janus Kinase 1 / Q000378:metabolism; D008545:Melanoma / Q000276:immunology / Q000378:metabolism* / Q000473:pathology; D051379:Mice; D010766:Phosphorylation; D050794:STAT1 Transcription Factor / Q000378:metabolism*; D050795:STAT2 Transcription Factor / Q000032:analysis; D050796:STAT3 Transcription Factor / Q000378:metabolism; D050799:STAT5 Transcription Factor / Q000378:metabolism