Die kooperative Rolle der Methyltransferasen CARM1 und PRMT1 in der Genregulation

The arginine methyltransferases CARM1 and PRMT1 are transcriptional coactivators. The vast majority of publications to date describe either one or the other methyltransferase as a coactivator for distinct transcription factors. However, both enzymes are cooperative regulators in the activation of nuclear hormone receptor and p53 target genes. First of all gene expression profiling was performed by means of a 11552 cDNA-Chip to identify novel target genes of CARM1. Upon treatment of HEK293 cells with an siRNA specific against CARM1 the immediate early response genes Egr1 and c-Fos were strongly upregulated. However, these genes did not depend on CARM1 since knock-downs performed with alternative siRNAs against the enzyme showed no change in expression of Egr1 and c-Fos. Consequently, subsequent microarray-analysis were carried out with two alternative siRNAs in order to rule out off-targets. We extended the experimental approach and performed gene expression profilings in HeLa cells upon loss of either one or both enzymes, CARM1 and PRMT1. The loss of one methyltransferase caused hardly measurable alterations in the expression profile of the cells. By contrast, the loss of both enzymes resulted in a more than twofold deregulation of 45 genes. Promoter analysis of those genes that were downregulated upon loss of both enzymes showed an enrichment of binding sites amongst others for the transcription factor STAT5. In a reporter gene assay we verified CARM1 and PRMT1 as cooperative coactivators for STAT5. Interleukin-4 stimulates the activation of STAT5 in HeLa cells. Upon loss of CARM1 and PRMT1 a subset of downregulated genes from the array failed to respond to Interleukin-4. However, the same targets were still inducible by serum. Taken together, in this study we uncover the cooperative effects among CARM1 and PRMT1 in vivo by gene expression profiling. Moreover, we provide evidence, that CARM1 and PRMT1 are transcriptional coactivators of STAT5 in the Interleukin-4 pathway.