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Original Investigation
October 2016

Analysis of the Expression and Single-Nucleotide Variant Frequencies of the Butyrophilin-like 2 Gene in Patients With Uveal Melanoma

Author Affiliations
  • 1Laboratory of Molecular Pathology, Istituto di Ricovero e Cura a Carattere Scientifico Azienda Ospedaliera Universitaria San Martino–IST Istituto Nazionale per la Ricerca sul Cancro, Genova, Italy
  • 2Department of Earth Sciences, Environment, and Life, Università Degli Studi di Genova, Genova, Italy
  • 3Intergruppo Melanoma Italiano, Genova, Italy
  • 4TIB-Molbiol Syntheselabor, Berlin, Germany
  • 5Ente Ospedaliero Galliera, Genova, Italy
  • 6Department of Tumor Epigenetics, Istituto di Ricovero e Cura a Carattere Scientifico Azienda Ospedaliera Universitaria San Martino–IST Istituto Nazionale per la Ricerca sul Cancro, Genova, Italy
  • 7Azienda Socio Sanitaria Territoriale Ospedale Papa Giovanni XXIII, Bergamo, Italy
  • 8Department of Genetics of Rare Tumors, Istituto di Ricovero e Cura a Carattere Scientifico Azienda Ospedaliera Universitaria San Martino–IST Istituto Nazionale per la Ricerca sul Cancro, Genova, Italy
  • 9Department of Blood Transfusion Center, Istituto di Ricovero e Cura a Carattere Scientifico Azienda Ospedaliera Universitaria San Martino–IST Istituto Nazionale per la Ricerca sul Cancro, Genova, Italy
  • 10Department of Anatomy and Cytohistopathology, Istituto di Ricovero e Cura a Carattere Scientifico Azienda Ospedaliera Universitaria San Martino–IST Istituto Nazionale per la Ricerca sul Cancro, Genova, Italy
  • 11Ospedale Villa Scassi, Genova, Italy
  • 12Department of Clinical Epidemiology, Istituto di Ricovero e Cura a Carattere Scientifico Azienda Ospedaliera Universitaria San Martino–IST Istituto Nazionale per la Ricerca sul Cancro, Genova, Italy
  • 13Laboratory of Molecular Biology, Istituto Giannina Gaslini, Genova, Italy
  • 14Institute of Human Genetics, Faculty of Medicine, University Duisburg-Essen, West German Cancer Center and the German Cancer Consortium, Essen, Germany
  • 15Department of Medical Oncology, Istituto di Ricovero e Cura a Carattere Scientifico Azienda Ospedaliera Universitaria San Martino–IST Istituto Nazionale per la Ricerca sul Cancro, Genova, Italy
JAMA Ophthalmol. 2016;134(10):1125-1133. doi:10.1001/jamaophthalmol.2016.2691
Key Points

Question  Does the butyrophilin-like 2 gene, an immune regulator, play a role in the risk and progression of uveal melanoma?

Findings  In this case-control study, butyrophilin-like 2 was expressed in uveal melanoma tumor cells and in macrophages, especially in M2-polarized macrophages. Macrophage polarization genes were associated with uveal melanoma metastasis risk, and butyrophilin-like 2 variants showed variable frequencies among ethnically related cohorts, but no association was evident between butyrophilin-like 2 and the risk to develop uveal melanoma.

Meaning  These findings suggest that inflammation plays a role in the development and progression of uveal melanoma, and butyrophilin-like 2 might play a role in the immune control of uveal melanoma and therefore could be a therapeutic target.

Abstract

Importance  Chromosome 6p amplification is associated with more benign behavior for uveal melanomas (UMs) with an otherwise high risk of metastasis conferred by chromosome 3 monosomy. Chromosome 6p contains several members of the B7 family of immune regulator genes, including butyrophilin-like 2 (BTNL2; OMIM, 606000), which is associated with prostate cancer risk and autoimmune diseases.

Objective  To investigate the expression and variant allele frequencies of BTNL2, a candidate gene for chromosome 6 amplification, in patients with UM.

Design, Setting, and Participants  In this case-control study, we analyzed the expression of BTNL2 in UM cell lines and human macrophages in patients with UM. Variants of BTNL2 were analyzed using probes for polymerase chain reaction and high-resolution melting. The association of missense variants rs28362679 and rs41441651 with tumor risk was analyzed in 209 patients with UM and 116 matched control patients as well as 12 UM and 64 other tumor cell lines. Genes that were differentially expressed in M1- and M2-polarized macrophages were identified by microarray analysis of 111 patients with UM, and the association of the expression of these genes with disease-free survival was analyzed by Cox regression analysis. Data were collected from September 2013 to November 2015.

Main Outcomes and Measures  Butyrophilin-like 2 single-nucleotide variants were associated with UM risk; M1 and M2 macrophage-specific gene expression was associated with disease-free survival.

Results  We genotyped a total of 325 patients. Of the 209 patients with UM, 124 (59.3%) were male, 114 (54.5%) were Italian, and 95 (45.5%) were German; the mean (range) age was 65 (27-94) years. Of the 116 Italian control patients, 67 (57.8%) were female, and the mean (range) age was 39 (21-88) years. Butyrophilin-like 2 is expressed in patients with UM and macrophages. The frequency of the rs28362679 variant was higher in patients with UM (16 of 209 [7.7%]; 95% CI, 4.7-12.2) than frequencies from European Variation Archive and Exome Aggregation Consortium data (2134 of 118 564 [1.8%]; 95% CI, 1.7-1.9) and Exome Sequencing Project data (100 of 4540 [2.2%]; 95% CI, 1.8-2.7) but were not higher compared with Italian control patients (10 of 116 [8.6%]; 95% CI, 4.6-15.4). The rs41441651 variant was present in 5 patients with UM (2.4%; 95% CI, 0.9-5.7), 2 Italian control patients (1.7%; 95% CI, 0.1-6.5), 2846 patients from European Variation Archive and Exome Aggregation Consortium data (2.4%; 95% CI, 2.3-2.5), and 23 patients from Exome Sequencing Project data (0.5%; 95% CI, 0.3-0.8). Human UM cells express M1 and M2 macrophage-specific genes, whose expression is associated with disease-free survival.

Conclusions and Relevance  Butyrophilin-like 2, expressed at various levels by UM cells and macrophages, might interfere with the immune control of the tumor. Butyrophilin-like 2 variants showed highly variable frequencies among ethnically related cohorts. There was no enrichment of BTNL2 variants in patients with UM compared with control patients.

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