In vitro assessment of the inflammatory breast cancer cell line SUM 149: Discovery of two single nucleotide polymorphisms in the RNase L gene.

Abstract

196 Background: Inflammatory breast cancer (IBC) is a rare, aggressive form of breast cancer, accounting for 5% of breast cancers diagnosed annually in the United States. Understanding the distinct biology of IBC could help provide novel treatment targets. We sought to evaluate whether or not the IBC cell lines SUM 149 and SUM 190 demonstrated evidence of viral infection. Methods: We performed single nucleotide polymorphism (SNP) genotyping for 2 variants of the ribonuclease (RNase) L gene that have been correlated with the risk of prostate cancer due to a possible viral etiology. We also performed proliferation assays; developed dose response curves to assess the treatment effect of interferon-alpha (IFN-a); and assayed for evidence of the putative human mammary tumor virus (HMTV, which has been implicated but not definitively associated with IBC,) in the DNA and RNA of SUM 149 cells. Results: According to our allelic discrimination SNP assay, 2/2 IBC cell lines were homozygous for the 462 and 541 variants, whereas 0/10 non-IBC cell lines were homozygous positive for the 462 variant (p = 0.015) and 2/10 non-IBC cell lines contained homozygous alleles for the 541 variant (p = 0.52). We also found a dose and time-dependent decrease in the proliferation of SUM 149 IBC cells treated with IFN-a. In contrast, non-IBC cell lines did not show a dose-response decrease in cell proliferation. Our reverse transcriptase polymerase chain reaction (RT-PCR) and Southern blot analysis for the env/LTR and late LTR sequences of the putative HMTV revealed no evidence of the putative viral genome. Conclusions: We discovered 2 SNPs, in the 462 and 541 variants of the RNase L gene, that were homozygously mutated in IBC cell lines but the 462 variant was absent in non-IBC lines. Our discovery of these mutated SNPs present in IBC cell lines suggests a possible genetic risk factor for IBC. In our study, the IBC cell line SUM 149 demonstrated a direct and specific response to treatment with IFN-a, an antiviral agent. We noted no evidence of HMTV infection in that cell line. Further studies of the prevalence and significance of the RNase L 462 and 541 variants in human IBC tissue specimens are warranted to validate our in vitro findings.