Characterization of TROM, a novel transcription repressor in human cancers identified by modified suppression subtractive Hybidization (MSSH)

Abstract

In order to understand cancer at its fundamentals, we developed a method termed modified suppression subtractive hybridization (mSSH), to discover low abundance yet cancer specific genes. Our strategy entails the generation of unidirectional anti-sense RNA following subtraction, allowing it to be used in conjunction with oligonucleotide (Affymetrix) arrays. Using this strategy, the detection sensitivity of low abundance transcripts was significantly enhanced. With mSSH, we identified common and specific gene signatures for Hepatocellular carcinoma (HCC), Breast carcinoma, and Nasopharyngeal carcinoma (NPC). The highest expressed gene in the common gene set was selected for further characterization, and it was named Transcription Repressor of MHCII (TROM). Exogenous over-expression of TROM leads to the marked reduction in the level of HLA-DRA mRNA. Similarly, silencing of the TROM gene resulted in an increase in the level of HLA-DRA. Further investigation showed that TROM represses HLA-DRA by competing against the transcription activators in promoter binding activity. In addition, TROM deactivates STAT1 (an upstream regulator of MHCII) during the induction of IFNN3, and contributed to its degradation. Moreover, the repression of HLA-DRA by TROM could be recapitulated in various human cancers, which in turn promotes cancer formation and progression. In conclusion, we have identified a novel cancer-specific transcription repressor by using the method of mSSH.