Together, these results strongly support the existence of a direct protein-protein interaction between Mdm2 and L26

Together, these results strongly support the existence of a direct protein-protein interaction between Mdm2 and L26. To characterize the Mdm2 interaction domain, we performed Co-IP assays with two Mdm2 deletion mutants, one lacking the Eslicarbazepine Acetate C-terminal RING domain (deletion of amino acids 441491; Mdm2R) and the other lacking the acidic domain (deletion of amino acids 239301; Mdm2A). is subject to exquisite regulation. One key regulator of p53 is the Mdm2 (mouse double minute 2) protein, which binds specifically to p53 and inhibits many of p53s biochemical activities (Marine et al., 2006;Michael and Oren, 2003). Furthermore, as a p53-selective E3-ubiquitin ligase, Mdm2 promotes p53 polyubiquitylation and targets p53 to degradation by the 26S proteasome (Fang et al., 2000;Haupt et al., 1997;Honda et al., 1997;Kubbutat et al., 1997). As theMdm2gene is a transcriptional target of p53, Mdm2 and p53 form a negative feedback loop, which ensures that p53 is maintained at low levels under normal conditions (Barak et al., 1993;Lahav et al., 2004;Wu et al., 1993) and is of vital importance to cellular homeostasis. Numerous mechanisms regulate the p53-Mdm2 axis, enabling optimal coupling of the particular triggering stress with the ensuing cellular Tmeff2 response. Under stress conditions, various mechanisms render p53 less affected by Mdm2. Such mechanisms include enhanced Mdm2 degradation, post-translational modifications on p53 and Mdm2, altered binding to other proteins that modulate the p53-Mdm2 interaction and its consequences, and altered sub-cellular localization of p53 and Mdm2 (reviewed in (Marine et al., 2006;Oren, 2003;Toledo and Wahl, 2006)). The Mdm2 protein comprises several distinct, highly conserved regions. The N-terminal domain harbors the main p53 binding interface. Two other notable regions of Mdm2 are the central domain (amino acids ~200300), often referred to as the acidic domain (AD), and the C-terminal RING domain (amino acids 438478). The latter is the enzymatic heart of Mdm2, enabling its E3-ubiquitin ligase activity, while the acidic domain is a hub for many protein-protein interactions that regulate Mdm2 function (Oren 2003). The acidic domain contributes to p53 degradation in at least two distinct ways. On the one hand, it harbors an additional p53 binding site (Kulikov et al., 2006;Ma et al., 2006;Wallace et al., 2006;Yu et al., 2006), required for efficient p53 polyubiquitylation, while on the other hand it mediates a post-ubiquitylation step required for proteasomal degradation of p53 (Argentini et al., 2001), which may involve direct binding of Mdm2 to the proteasome (Sdek et al., 2005). Mdm2 interacts with a variety of ribosomal proteins, including L5, L11, L23 and S7 (Chen et al., 2007;Dai and Lu, 2004;Dai et al., 2004;Jin et al., 2004;Lindstrom et al., 2007;Lohrum et al., 2003;Marechal et al., 1994;Zhang et al., 2003). These interactions, which typically involve the acidic domain and sometimes the adjacent zinc finger of Mdm2, interfere with the inhibitory functions of this region of Mdm2 and contribute to p53 activation. As first exemplified for L11 (Lohrum et al., 2003), these interactions increase when ribosome biogenesis is disrupted, a situation termed ribosomal biogenesis stress or nucleolar stress (Pestov et al., 2001;Rubbi and Milner, 2003). Such stress can be induced by Eslicarbazepine Acetate drugs that inhibit RNA polymerase I, e.g., low levels of actinomycin D (Bhat et al., 2004;Lohrum et al., 2003), 5-FU (Gilkes et al., 2006), or other growth inhibitory conditions such as serum starvation and contact inhibition (Bhat et al., 2004). Mechanistically, ribosomal stress causes translocation of free ribosomal proteins from the nucleolus to the nucleoplasm (Bhat et al., 2004;Lam et al., 2007), where they bind Mdm2 (Bhat et al., 2004). The increased binding of ribosomal proteins to Mdm2 augments cellular p53 activity, leading to growth arrest and coupling deficient protein synthesis with cessation of cell proliferation. We have previously described the use of a yeast two-hybrid screen (Y2H) to Eslicarbazepine Acetate discover proteins that interact with the Mdm2 acidic domain, leading to identification of the Lats2 tumor suppressor as a novel regulator of the p53-Mdm2 axis (Aylon et al., 2006). We now report, using the same Y2H approach, that the ribosomal protein L26 (RPL26) also interacts specifically with Mdm2. Interestingly, L26 is an.