dCas9-metabolic enzyme fusions modulate global and locus-specific gene expression.

Central metabolites function as essential co-substrates for chromatin-modifying enzymes, directly linking cellular metabolism to chromatin regulation. Accordingly, whole-cell fluctuations in co-substrate availabilities have been shown to promote diverse phenotypes through chromatin-dependent mechanisms. There is emerging evidence that metabolic enzymes producing co-substrates for chromatin modifying enzymes can exist in the nucleus, suggesting that nucleus-specific metabolite availability regulates chromatin state. Here, we developed CRISPRm (CRISPR metabolite) to assess how nucleus-specific metabolic perturbations influence chromatin function. Five dCas9-metabolic enzyme fusions (i.e., dCas9-ACSS2, -NMNAT1, -MAT2A, -GDH, and -AHCY) were used to modulate nuclear levels of essential co-substrates involved in histone (de)acetylation and (de)methylation reactions. Transient expression of all dCas9 fusions in HEK293T cells induced distinct global changes in gene expression patterns, with dCas9-ACSS2 (acetyl-CoA producing) and NMNAT1 (NAD+ producing) eliciting large opposing changes in gene expression, suggesting transcriptional responses to nuclear acetyl-CoA and NAD+ production may be directly facilitated by acetylation or deacetylation reactions, respectively. Targeting dCas9-ACSS2 and -NMNAT1 to promoters of select candidate genes revealed enhanced transcriptional modulation. dCas9-ACSS2 upregulated, and dCas9-NMNAT1 downregulated genes showed basal enrichment of H3K9ac, H3K18ac, H3K27ac, H3K4me3, and p300, suggesting these genomic loci reside within epigenetic environments susceptible to fluctuations in acetyl-CoA and NAD+ availability. Of significant genes altered, dCas9-MAT2A (SAM producing) increased expression of 72% whereas dCAS9-GDH (alpha-ketoglutarate producing) decreased expression of 79%. Surprisingly, dCAS9-AHCY (SAH hydrolysis) led to down-regulation of shared genes up-regulated by dCas9-MAT2A. The observations amongst the methylation-specific enzymes revealed unexpected and unique gene-regulatory sensitivities to SAM, SAH and alpha-ketoglutarate. Together, these results demonstrate the utility of CRISPRm in studying nuclear metabolic regulation of transcription and provide strong evidence that perturbations in nuclear co-substrates do not lead to a large mass- action changes in chromatin acetylation/methylation but rather to modulation of select chromatin-modifying enzymes with targeted transcription responses.