NO2 study

NO effects on gene expression, independent of cGMP, were examined globally. Differentiated human U937 cells that lack soluble guanylate cyclase were exposed to Snitrosoglutathione, a NO donor, or glutathione without or with dibutyryl-cAMP (Bt2cAMP). NO regulated 110 transcripts that annotated disproportionately to the cell cycle and cell proliferation (47/110, 43%) and more frequently than expected contained AU-rich, post-transcriptional regulatory elements (ARE). Bt2cAMP regulated 106 genes; cell cycle gene enrichment did not reach significance. Like NO, Bt2cAMP was associated with ARE-containing transcripts. Cell cycle genes induced by NO were G1/S phase associated (7/8) including E2F1 and p21/Waf1/Cip1; 6 of these 7 were E2F target genes involved in G1/S transition. Repressed genes were G2/M associated (24/27); 8 of 27 were known targets of p21. E2F1 mRNA and protein were increased by NO, as was E2F1 binding to E2F promoter elements. NO activated p38 MAPK, stabilizing p21 mRNA and increasing p21 protein. Subsequent increases in protein binding to CDE/CHR sites repressed key G2/M phase genes and increased the proportion of cells in G2/M. Thus, NO triggers a specific and coordinated program of cell cycle arrest independent of cGMP. Stress kinase pathways and mRNA stability are major mechanisms by which NO regulates the transcriptome. Keywords: other