Total HLA class I loss in a sarcomatoid renal carcinoma cell line caused by the coexistence of distinct mutations in the two encoding β2-microglobulin genes
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In renal cell carcinoma (RCC), HLA class I downregulation has been found in about 40% of the lesions examined. Since only scanty information is available about the molecular basis of these defects, we have investigated the mechanism(s) underlying HLA class I antigen downregulation or loss in six RCC cell lines. Five of them express HLA class I antigens although at various levels; on the other hand, HLA class I antigens are not detectable on the remaining cell line, the RCC52 cell line, belonging to a sarcomatoid subtype, even following incubation with IFN-γ. β2-microglobulin (β2 m) was not detected in RCC52 cells. Surprisingly, RCC52 cells harbor two mutations in the β 2 m genes in exon 1: a single G deletion (delG) in codon 6, which introduces a premature stop at codon 7, and a CT dinucleotide deletion (delCT), which leads to a premature stop at codon 55. Analysis of eight clonal sublines isolated from the RCC52 cell line showed that the two β 2 m gene mutations are carried separately by RCC52 cell subpopulations. The delG/delCT double mutations were detected in two sublines with a fibroblast-like morphology, while the delCT mutation was detected in the remaining six sublines with an epithelial cell morphology. Furthermore, loss of heterozygosity (LOH) of the β 2 m gene at STR D15S-209 was found only in the epithelioid subpopulation, indicating loss of one copy of chromosome 15. Immunostaining results of the tumor lesion from which the cell line RCC52 was originated were consistent with the phenotyping/molecular findings of the cultured cells. This is the first example of the coexistence of distinct β 2 m defects in two different tumor subpopulations of a RCC, where loss of one copy of chromosome 15 occurs in one of the subpopulations with total HLA class I antigen loss.
KeywordsHLA class I β2-Microglobulin Renal cell carcinoma Sarcomatoid subtype Cell lines
The authors wish to thank Tzu-Ju Chang, Chen-Chen Kang, and Hung-Chang Chen for their excellent technical assistance. Special thanks are also expressed to late Dr. Shanka K Nayak, Hoag Cancer Center, Newport Beach, CA, for providing the HH050, HH244 and HH332 cell lines and to Dr. Yukiyo Yoshida, Hasumi International Research Foundation, Tokyo Laboratory, Suginami, Japan, for the HOKN-9 cell line to be used in this study. This study was supported in part by the National Science Council of Taiwan (NSC93-2314-B-182-022; NSC94-2314-B-182-060) and the Chang Gung Medical Research Fund (CMRP-363) awarded to S-K.L, by the NSC grant NSC97-2923-B-007-002-MY2 to C-C.C, and by National Cancer Institute, DHHS (USA) PHS grants RO1CA67108 and RO1CA110249 to S.F.
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