A Lin-9 complex is recruited by B-Myb to activate transcription of G2/M genes in undifferentiated embryonal carcinoma cells

Abstract

It has recently been discovered that cell-cycle gene transcription is regulated by a core complex named LINC that switches from a transcriptionally repressive complex in G 0 -G 1 with the p130 or p107 pocket proteins and E2F4 to a transcriptionally active complex in S-G 2 containing B-Myb. We have studied the function of LINC in F9 embryonal carcinoma cells, which are distinguished by a rapid cell cycle resulting from an extremely short G 1 phase. We show that suppressing expression of the LINC component, Lin-9, in F9 cells causes arrest in mitosis, and we have used this system to screen for transcriptional targets. In these cells, B-Myb was found in complexes with Lin-9 and several other LINC constituents, however, the pocket proteins did not associate with LINC unless F9 cells were differentiated. Lin-9 and B-Myb were both required for transcription of G 2 /M genes such as Cyclin B1 and Survivin. Moreover, B-Myb was demonstrated to recruit Lin-9 to the Survivin promoter through multiple Myb-binding sites. The demonstration that a B-Myb/ LINC complex is vital for progression through mitosis in cells lacking a G 1 /S checkpoint has implications for both undifferentiated embryonal cells and for cancers in which pocket protein function is compromised.

Loss of LIN9, a member of the DREAM complex, cooperates with SV40 large T antigen to induce genomic instability and anchorage-independent growth

“…In recent studies, the DREAM complex has emerged as a master regulator of mitotic gene expression during the cell cycle (Litovchick et al, 2007;Osterloh et al, 2007;Schmit et al, 2007;Pilkinton et al, 2007a;Knight et al, 2009). Loss of LIN9, a core subunit of DREAM, Loss of LIN9, a member of the DREAM complex S Hauser et al in conditional knockout MEFs severely abolishes the ability of the cells to proliferate and to progress through mitosis and cytokinesis because of reduced expression of mitotic genes (Reichert et al, 2010).…”

“…The DREAM (or LINC) complex is a master regulator of mitotic gene expression during the cell cycle (Schmit et al, 2007, reviewed in Blais and Dynlacht, 2007;Litovchick et al, 2007;Osterloh et al, 2007;Pilkinton et al, 2007a;Knight et al, 2009). Several proteins that are involved in chromosome segregation and cytokinesis, such as Bub1 and survivin, are direct targets of DREAM (Osterloh et al, 2007;Schmit et al, 2007;Pilkinton et al, 2007b;Knight et al, 2009).…”

“…Several proteins that are involved in chromosome segregation and cytokinesis, such as Bub1 and survivin, are direct targets of DREAM (Osterloh et al, 2007;Schmit et al, 2007;Pilkinton et al, 2007b;Knight et al, 2009). DREAM consists of a fiveprotein core module and associated proteins (Litovchick et al, 2007;Schmit et al, 2007;Pilkinton et al, 2007a;Knight et al, 2009).…”

“…In the Sphase, binding to E2F4/p130 is lost and another transcription factor, B-MYB, is incorporated into the complex. DREAM, together with E2F4 and p130, contributes to the repression of E2F-regulated genes in G0/G1, whereas DREAM-B-MYB is essential for gene activation in G2/M (Litovchick et al, 2007;Osterloh et al, 2007;Schmit et al, 2007;Pilkinton et al, 2007a;Knight et al, 2009). RNA interference-mediated knockdown of DREAM subunits in human cells inhibits their proliferation owing to inhibition of mitotic gene expression (Osterloh et al, 2007;Schmit et al, 2007).…”

B- myb is an essential regulator of hematopoietic stem cell and myeloid progenitor cell development

“…In their steady-state, HSCs are largely quiescent and enter the cell cycle in response to stimuli that trigger differentiation and lineage commitment (18). B-myb has been shown to play a role in the cell cycle progression of multiple cell types and is involved in regulating progression through the S and G 2 /M phases (19)(20)(21)(22)(23)(24)(25). To determine whether loss of B-myb expression led to altered cell cycle kinetics in HSCs, pIpC-treated control and B-myb F/Fcre mice were injected with BrdU and BM was harvested 2 h posttreatment.…”