Transactivation mediated by B-Myb is dependent on TAFII250

Abstract

B-Myb is a highly conserved member of the Myb family of transcription factors, which has been implicated in cell cycle regulation. B-Myb is expressed in most proliferating cells and its activity is highly regulated around the G1/Sphase border of the cell cycle. It is generally assumed that B-Myb regulates the expression of genes that are crucial for cell proliferation; however, the identity of these genes, the molecular mechanisms by which B-Myb stimulates their expression and the involvement of other proteins have not been sufficiently clarified. We have employed the hamster cell line ts13 as a tool to demonstrate a functional link between B-Myb and the coactivator TAF II 250, a key component of the transcriptional machinery which itself is essential for cell proliferation. ts13 cells express a pointmutated version of TAF II 250 whose intrinsic histone acetyl transferase activity is temperature sensitive. Transactivation of Myb-responsive reporter genes by BMyb is temperature-dependent in ts13 cells but not in ts13 cells, which have been rescued by transfection with an expression vector for wild-type TAF II 250. Furthermore, B-Myb and TAF II 250 can be coprecipitated, suggesting that both proteins are present in a complex. The formation of this complex is dependent on the DNA-binding domain of B-Myb and not on its transactivation domain. Taken together, these observations provide the first evidence that the coactivator TAF II 250 is involved in the activation of Myb responsive promoters by B-Myb. The finding that BMyb transactivation is dependent on a key coactivator involved in cell cycle control is consistent with and strengthens the idea that B-Myb plays a crucial role as a transcription factor in proliferating cells.

MYBL2 (B-Myb): a central regulator of cell proliferation, cell survival and differentiation involved in tumorigenesis

“…24 Several other co-activators, such as PARP1, ZPR9, TAF(II)250, or co-repressors, such as p107, p57 or CDK9, were further shown to modulate transactivation properties of MYBL2. 26, 27, 28, 29, 30, 31, 32, 33 …”

Regulation of the cyclin D1 and cyclin A1 promoters by B-Myb is mediated by Sp1 binding sites

“…Phosphorylation of B-Myb by cyclin A/Cdk2 in the early S-phase of the cell cycle stimulates the transactivation potential of BMyb by counteracting the repressive function of an inhibitory domain located at the carboxyl-terminus (Robinson et al, 1996;Lane et al, 1997;Sala et al, 1997;Ziebold et al, 1997;Saville and Watson, 1998b;Bartsch et al, 1999). Several B-Myb interacting proteins have been identified and shown to affect the B-Myb transactivation potential, including cyclin D1 (Horstmann et al, 2000;Schubert et al, 2004), poly-(ADP-ribose) polymerase (PARP) (Cervellera and Sala, 2000), p107 (Joaquin et al, 2002), nucleolin (Ying et al, 2000), p300 (Bessa et al, 2001;Johnson et al, 2002;Schubert et al, 2004), TAFII250 (Bartusel and Klempnauer, 2003) and N-CoR/SMRT (Masselink et al, 2001;Li and McDonnell, 2002). The interactions of some of these proteins, such as PARP (Santilli et al, 2001), N-CoR/SMRT (Li and McDonnell, 2002) and p300 (Schubert et al, 2004), appear to be modulated by the phosphorylation state of B-Myb suggesting that they are involved in the phosphorylation-dependent stimulation of B-Myb activity.…”

Interplay with the Mre11-Rad50-Nbs1 complex and phosphorylation by GSK3β implicate human B-Myb in DNA-damage signaling

“…Notably, phosphorylation of B-Myb by Cyclin A/Cdk2 at the onset of S-phase stimulates its transactivation potential by relieving repressive effects exerted by its C-terminal domain and also triggers its degradation by the ubiquitin-dependent Cdc34-SCF p45Skp2 pathway 11 12 13 14 15 16 17 . B-Myb has been shown to interact with several other proteins in addition to the MuvB complex, including cyclin D1 18 19 , poly-(ADP-ribose) polymerase (PARP) 20 , nucleolin 21 , p300 19 22 , TAFII250 23 and N-CoR/SMRT 24 .…”