SNR1 (INI1/SNF5) mediates important cell growth functions of the Drosophila Brahma (SWI/SNF) chromatin remodeling complex

SNR1 is an essential subunit of the Drosophila Brahma (Brm) ATP-dependent chromatin remodeling complex, with counterparts in yeast (SNF5) and mammals (INI1). Increased cell growth and wing patterning defects are associated with a conditional snr1 mutant, while loss of INI1 function is directly linked with aggressive cancers, suggesting important roles in development and growth control. The Brm complex is known to function during G, phase, where it appears to assist in restricting entry into S phase. In Drosophila, the activity of DmcycE/CDK2 is rate limiting for entry into S phase and we previously found that the Brm complex can suppress a reduced growth phenotype associated with a hypomorphic DmcycE mutant. Our results reveal that SNR1 helps mediate associations between the Brm complex and DmcycE/CDK2 both in vitro and in vivo. Further, disrupting snr1 function suppressed DmcycE(JP) phenotypes, and increased cell growth defects associated with the conditional snr1(E1) mutant were suppressed by reducing DmcycE levels. While the snr1(E1)-dependent increased cell growth did not appear to be directly associated with altered expression of G(1) or G(2) cyclins, transcription of the G(2)-M regulator string/cdc25 was reduced. Thus, in addition to important functions of the Brm complex in G(1)-S control, the complex also appears to be important for transcription of genes required for cell cycle progression.