Interaction of BTG1 and p53-regulatedBTG2 Gene Products with mCaf1, the Murine Homolog of a Component of the Yeast CCR4 Transcriptional Regulatory Complex

Abstract

Both BTG1 and BTG2 are involved in cell-growth control. BTG2 expression is regulated by p53, and its inactivation in embryonic stem cells leads to the disruption of DNA damage-induced G 2 /M cell-cycle arrest. In order to investigate the mechanism underlying Btg-mediated functions, we looked for possible functional partners of Btg1 and Btg2. Using yeast two-hybrid screening, protein-binding assays, and transient transfection assays in HeLa cells, we demonstrated the physical in vitro and in vivo interaction of both Btg1 and Btg2 with the mouse protein mCaf1 (i.e. mouse CCR4-associated factor 1). mCaf1 was identified through its interaction with the CCR4 protein, a component of a general transcription multisubunit complex, which, in yeast, regulates the expression of different genes involved in cell-cycle regulation and progression. These data suggest that Btg proteins, through their association with mCaf1, may participate, either directly or indirectly, in the transcriptional regulation of the genes involved in the control of the cell cycle. Finally, we found that box B, one of two conserved domains which define the Btg family, plays a functional role, namely that it is essential to the Btg-mCaf1 interaction.

Roles for p53 in growth arrest and apoptosis: putting on the brakes after genotoxic stress

“…p19 ARF has also been shown to bind p53 directly, and overexpressed p53 was impaired in its ability to induce both p21 CIP1/WAF1 and G1 arrest in arf7/7 MEFs, suggesting direct modulation of p53 transactivation activity by p19 ARF . Conversely, p19 ARF levels are unusually elevated in p537/7 MEFs (Rouault et al, 1998) and can be restored to normal by restoration of functional p53 , suggesting another autoregulatory loop between p53 and p19 ARF (Figure 2). A similar autoregulation operates between p53 and the product of the proto-oncogene c-Myc (Figure 2).…”

“…14-3-3 proteins can bind and sequester phosphorylated Cdc25C, thereby preventing its dephosphorylation and activation of Cdc2 , and providing another link between p53 and the G2 checkpoint. BTG2 has also recently been shown to be regulated by p53, and its inactivation in ES cells led to the disruption of DNA damageinduced G2/M arrest, perhaps through loss of interaction with mCaf1 and consequent transcriptional regulation of other cell cycle regulatory genes (Rouault et al, 1998). …”

Oligo-astheno-teratozoospermia in mice lacking Cnot7, a regulator of retinoid X receptor beta

“…In addition, proteins in the CCR4-NOT complex are involved in mRNA metabolism in yeast 5,6 . Two mammalian homologs of yeast CAF1 are known: Cnot7 (also called CAF1) and Cnot8 (also called CALIF) 7,8 . Both are expressed in a variety of tissues, with relatively high expression of Cnot7 in lung, liver and thyroid gland 7,8 .…”

AF15q14, a novel partner gene fused to the MLL gene in an acute myeloid leukaemia with a t(11;15)(q23;q14)

“…It will be interesting to see if this gene is found to be involved in other cases of t(11;15)(q23;q14). Immuno¯uorescence staining of Cos-7 cells was carried out after transient transfection, using Fugene 2 (Roche), either by the wild-type pSG5-¯ag vector (Rouault et al, 1998), used as a control (data not shown), or by the pSG5-¯ag expression vector which encodes the last 85 amino acids of AF15q14. The anti-Flag M2 monoclonal antibody (Stratagene) was used to detect the¯agAF15-85aa fusion protein (green).…”