Interferon Regulatory Factor-4 Is Expressed Infrequently in Metastatic Melanomas and Correlates with Amplification of the IRF4 Locus.
Andrew L Feldman, Lori A Erickson, Mark E Law, Julie C Porcher, Wendy K Nevala, Jacob B Allred, Svetomir N Markovic. Mayo Clinic, Rochester
Background: Interferon regulatory factor-4 (IRF4) is a transcription factor expressed in melanocytes and some melanomas, but its function in melanocytic cells is unknown. The IRF4 single nucleotide polymorphism allele, rs12203592*C, is a melanoma risk factor; this allele represses IRF4 promoter activity, raising the possibility that IRF4 protects against melanoma. IRF4 resides on 6p, a region often amplified in melanoma, suggesting IRF4 paradoxically might be up-regulated in advanced disease. We undertook this study to examine the relationship between IRF4 protein expression and IRF4 copy number in metastatic melanoma.
Design: We performed IRF4 immunohistochemistry (MUM1p, Dako) in 116 cases of metastatic cutaneous melanoma (87 M, 29 F; mean age, 57 y). Expression was scored as: 0 = <10% staining; 1 = 10-30% staining; 2 = >30% staining, weak; and 3 = >30% staining, strong. IRF4 amplification (>4 copies) or translocation was detected by fluorescence in situ hybridization using a breakapart probe. Associations with overall survival (OS) from time of biopsy were examined using the log-rank test. Metastatic melanoma cell lines were assayed for IRF4 expression (Western blot) and proliferation (EdU incorporation).
Results: Among tissue samples, IRF4 staining was seen in 25/116 (22%; 30% cutoff) or 38/116 (33%; 10% cutoff). IRF4 amplification was seen in 47/116 (41%). The mean IRF4 staining score significantly correlated with IRF4 gene amplification (0.93±1.00 vs 0.23±0.66 without amplification; p=0.00004, t test). One amplified case also had an IRF4 translocation. Median OS was slightly longer for patients with IRF4 expression (63.0 vs 41.0 mos) or IRF4 amplification (65.2 vs 41.9 mos), but these were not statistically significant. Cell line proliferation fractions were 92% in A375 (IRF4-negative), and 26% and 63% in C32TG and SK-MEL-28, respectively (IRF4-positive).
Conclusions: IRF4 is expressed in normal melanocytes, but, in contrast to one previous report, our data suggest IRF4 is expressed in only the minority of metastatic melanomas. IRF4 expression may have a protective effect in melanoma, becoming lost during melanoma development or progression. Indeed, proliferation fraction was highest in an IRF4-negative cell line. Paradoxically, IRF4 expression is associated with IRF4 amplification in metastatic melanoma. Since 6p amplification is associated with poor prognosis in melanoma, our inability to identify significantly improved OS in patients with IRF4 expression may be due to the opposing deleterious effects of other amplified genes on 6p in these patients.
Monday, February 28, 2011 2:15 PM
Platform Session: Section F, Monday Afternoon