Early events in transcription and genome organization after STAG2 reconstitution in human cancer cells [Hi-C]

Truncating mutations of the tumor suppressor gene STAG2, encoding a component of the chromatin-bound cohesin complex, are present in many human cancer types. Here we report for the first time the early effects of reconstituting physiological levels of wild-type STAG2 in STAG2-mutant human cancer cells. Acute STAG2 reconstitution only modestly affected global gene expression - <1% of genes were altered by two-fold or greater. Only EFEMP1, encoding a secreted extracellular matrix glycoprotein, was induced by STAG2 in all experimental systems tested. There were similarly modest effects on chromatin loops - <1% of all chromatin loops were altered in intensity. and no loops were entirely STAG2-dependent. Loops strengthened by STAG2 reconstitution tended to be small, consistent with prior observations that STAG2-cohesin has less loop extrusion processivity than STAG1-cohesin. The STAG2-regulated “immediate early genes” were not accompanied by STAG2-regulated enhancer-promoter chromatin loops and no chromatin features were identified by integrative bioinformatics with newly generated ChIP-seq and ATAC-seq data that could explain their regulation by STAG2. Together these data indicate that the number of genes directly regulated by STAG2-cohesin is small, suggest that current models are likely insufficient to explain the mechanism of direct transcriptional regulation by STAG2-cohesin, and identify EFEMP1 as a potential effector of STAG2 tumor suppression. Overall design: Human glioblastoma multiforme cell lines H4 and MOG-G-UVW (both with endogenous truncating mutations of the STAG2 tumor suppressor gene) were infected with adenoviral vector alone or a derivative expressing wild-type STAG2. 36 hours after infection the cells were harvested and prepared for Hi-C.