TI - p16INK4a does not require BRG1 to promote cell cycle arrest or induce cell senescence . AB - To thoroughly evaluate any functional interaction between p16INK4a and BRG1 , we stably silenced BRG1 in the inducible WMM1175 p16INK4a cell model . These cells were transfected with a silencing molecule specifically targeting BRG1 or a non-specific ( NS ) silencing molecule directed to the luciferase transcript . Two BRG1-silenced clones , WMM1175 p16INK4a siBRG1 W9 and X1 , with gt 95% reduction in BRG1 accumulation and two control clones WMM1175 p16INK4a sicontrol E1 and X2 , with unaltered BRG1 expression , were selected for analysis . All clones remained inducible for p16INK4a expression ( Figure 5A , B ) . Silencing of BRG1 had no significant impact on the proliferation rate or cell cycle distribution of the WMM1175 p16INK4a cell line . In the absence of BRG1 , p16INK4a retained the ability to inhibit the proliferation of the WMM1175 cells (Figure 5C) , and this was associated with arrest in the G1-phase of the cell cycle with a concomitant S-phase inhibition ( Figure 5D ) that was maintained over the five-day induction period ( data not shown ) . Moreover , the silencing of BRG1 had no impact on the ability of p16INK4a to totally prevent outgrowth of colonies upon low seeding density ( Figure 5E ) . BRG1 has been reported to induce senescence in SW-13 cells and in mesenchymal stem cells [7,19] and the role of p16INK4a in initiating and maintaining senescence is widely acknowledged ( reviewed by Huschtscha & Reddel [20] ) . We investigated the role of BRG1 in p16INK4a -induced senescence . The long term induction of p16INK4a in WMM1175 p16INK4a cells was not influenced by the BRG1 status , caused pRb hypoPHOSphorylation (Figure 6A) and induced senescence-like features in the WMM1175 cells as reported previously [18,21] , ( Figure 6B ) . These features included increased cell size and granularity , positive senescence-associated beta-galactosidase activity and the appearance of senescence-associated heterochromatin foci . Formation of foci coincides with the recruitment of pRb to E2F-responsive promoters and is associated with the stable repression of E2F-target genes [22] . This important marker of pRb activity was not affected by BRG1 silencing . Similarly , BRG1 silencing did not alter the build up of SA-beta-galactosidase induced by p16INK4a (Figure 6B) or p16INK4a induced changes in cell size and granularity in the WMM1175 cells (Figure 6C) , the latter corresponds to senescence associated vacuolisation . This data confirms that cell cycle regulation and induction of cell senescence by p16INK4a does not require BRG1 .