Brm transactivates the telomerase reverse transcriptase (TERT) gene and modulates the splicing patterns of its transcripts in concert with p54nrb

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Abstract
We report that a DBHS (Drosophila behaviour, human splicing) family protein, p54nrb, binds both BRG1 (Brahma-related gene 1) and Brm (Brahma), catalytic subunits of the SWI/SNF (switch/sucrose non-fermentable) chromatin remodelling complex, and also another core subunit of this complex, BAF60a. The N-terminal region of p54nrb is sufficient to pull-down other core subunits of the SWI/SNF complex, suggesting that p54nrb binds SWI/SNF-like complexes. PSF (polypyrimidine tract-binding protein-associated splicing factor), another DBHS family protein known to directly bind p54nrb, was also found to associate with the SWI/SNF-like complex. When sh (short hairpin) RNAs targeting Brm were retrovirally expressed in a BRG1-deficient human cell line (NCI-H1299), the resulting clones showed down-regulation of the TERT (telomerase reverse transcriptase) gene and an enhancement of ratios of exon-7-and-8-excluded TERT mRNA that encodes a β-site-deleted inactive protein. All of these clones display growth arrest within 2 months of the Brm-knockdown. In NCI-H1299 cells, Brm, p54nrb, PSF and RNA polymerase II phosphorylated on CTD (C-terminal domain) Ser2 specifically co-localize at a region incorporating an alternative splicing acceptor site of TERT exon 7. These findings suggest that, at the TERT gene locus in human tumour cells containing a functional SWI/SNF complex, Brm, and possibly BRG1, in concert with p54nrb, would initiate efficient transcription and could be involved in the subsequent splicing of TERT transcripts by accelerating exon-inclusion, which partly contributes to the maintenance of active telomerase.

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