The coincidence of chromosome 15 aberrations and beta2-microglobulin gene mutations is causative for the total loss of human leukocyte antigen class I expression in melanoma.
OBJECTIVE
Total loss of surface presentation of human leukocyte antigen (HLA) class I molecules, protecting tumor cells from the recognition by cytotoxic host CD8+ T cells, is known to be caused by mutations in the beta2-microglobulin (beta2m) gene. We asked whether abnormalities of chromosome 15, harboring the beta2m gene on 15q21, in addition to beta2m gene mutations, are causative for the HLA class I-negative phenotype of melanoma cells.


METHODS
To answer this, we established primary cell lines from the beta2m-negative metastatic melanoma tissues of four different patients and analyzed them for beta2m gene mutations and chromosome 15 aberrations, the latter by loss of heterozygosity analysis, fluorescence in situ hybridization (FISH), and multicolor FISH.


RESULTS
Mutations at the beta2m gene level were detected in all cell lines. The loss of heterozygosity analysis of microsatellite markers located on chromosome 15 in three of the four cell lines pointed to an extensive loss of chromosome 15 material. Subsequent molecular cytogenetic analysis revealed the coexistence of apparently normal and rearranged versions of chromosome 15 in three cell lines whereas the fourth cell line solely showed rearranged versions. Two of the four cell lines exhibited a special type of intrachromosomal rearrangement characterized by FISH signals specific for the subtelomeric region of 15q at both ends of the chromosome and one centromeric signal in between.


CONCLUSIONS
Our data indicate that the complete loss of HLA class I expression in melanoma cells is due to the coincidence of the following mutational events: (a) chromosome 15 instability associated with an extensive loss of genetic material and (b) beta2m gene mutations.
Paschen
Annette
A
Skin Cancer Unit of the German Cancer Research Center Heidelberg, University Clinics of Mannheim, Mannheim, Germany. a.paschen@dkfz.de
Arens
Norbert
N
Sucker
Antje
A
Greulich-Bode
Karin M
KM
Fonsatti
Ester
E
Gloghini
Annunziata
A
Striegel
Sandra
S
Schwinn
Nicole
N
Carbone
Antonino
A
Hildenbrand
Ralf
R
Cerwenka
Adelheid
A
Maio
Michele
M
Schadendorf
Dirk
D
D045744:Cell Line, Tumor; D002869:Chromosome Aberrations; D002884:Chromosomes, Human, Pair 15 / Q000235:genetics*; D020869:Gene Expression Profiling; D015972:Gene Expression Regulation, Neoplastic; D015395:Histocompatibility Antigens Class I / Q000235:genetics*; D006801:Humans; D007150:Immunohistochemistry; D017404:In Situ Hybridization, Fluorescence; D008545:Melanoma / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D009154:Mutation; D010641:Phenotype; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D017384:Sequence Deletion; D019139:Tumor Escape / Q000235:genetics; D001613:beta 2-Microglobulin / Q000235:genetics*
D015395:Histocompatibility Antigens Class I; D001613:beta 2-Microglobulin