Role of EZH2 in Regulating EGR1 in Rhabdomyosarcoma

Abstract

Background: EGR1, one of the immediate-early response genes, plays an important role as a mediator for transmitting extracellular stimuli. EGR1 is down regulated in many cancers. Many studies show that it functions as a tumor suppressor gene in a variety of cancers. EGR1 also acts as an oncogene in number of cancers. We found that in rhabdomyosarcoma (RMS), which is a muscle derived pediatric cancer, EGR1 was expressed in both RMS subtypes, embryonal and alveolar, but with a much higher expression profile in embryonal RMS. This suggests different mechanisms of down regulation of EGR1 in these two subtypes. Methodology: Different Rhabdomyosarcoma cell lines were used. Gene expression was assessed by RT-qPCR. Then ChIP was performed to evaluate protein binding to EGR1 promoter. Results: The catalytic subunit of the PRC2 complex, EZH2, binds to the EGR1 promoter and represses the transcription of EGR1. This ultimately leads to the down regulation of EGR1 in RMS. The catalytic subunit of PRC2, EZH2, is a histone methyltransferase in which catalyzes tri-methylation of histone H3 lysine 27 (H3K27me3). We looked at the expression of one of the main targets of EGR1, PTEN, and we found an upregulation of PTEN mRNA expression investigate the mechanism by which EZH2 represses EGR1 and its target genes expression, we performed ChIP assays for EZH2 to the EGR1 promoter in both ARMS and ERMS cells, respectively. We found that EZH2 was strongly enriched on the EGR1 promoter in ARMS cells, RH30 and RD2. we also looked to the availability of EGR1 protein to bind and activate one of its main target genes, PTEN, which is a tumor suppressor gene. Conclusion: We concluded that targeting EZH2 therapeutically may be valuable in the treatment of RMS.