LDE225 956697-53-3 up near the carboxy terminal RING domain

up near the carboxy terminal RING domain. Mdm2 serine 17 near the amino terminus is phosphorylated by DNA PK in vitro. More recent biochemical studies have shown that this site is responsible for dictating the dynamic equilibrium of Mdm2 p53 interactions. Under homeostatic conditions, LDE225 956697-53-3 a large group of serine residues in the acidic domain are phosphorylated. This region becomes hypo phosphorylated under stress conditions. The acidic domain is important for target recruitment and ubiquitination. DNA damage also leads to phosphorylation of a more disperse group of serine and tyrosine residues mainly residing near the RING domain Waning et al. Page 3 Pharmaceuticals. Author manuscript, available in PMC 2010 July 21. NIH PA Author Manuscript NIH PA Author Manuscript NIH PA Author Manuscript with an additional site adjacent to the acidic domain.
DNA damage activates cell cycle checkpoints that lead to the robust activation of ATM and ATR kinase pathways. ATM is activated by DNA double strand breaks while Fludarabine ATR is activated by stalled replication forks. Direct phosphorylation of Mdm2 at serine 395 by ATM blocks nuclear export of p53 and leads to stabilization of p53 protein. ATM phosphorylation of Mdm2 at serine 386, 395, 425 and 428, and at threonine 419 cooperatively lead to stabilization of p53 by preventing poly ubiquitination, a consequence of preventing Mdm2 RING domain homo dimerization. ATR phosphorylates Mdm2 at serine 407 in response to specific types of DNA damage blocking nuclear export of p53. ATM also activates the downstream c Abl kinase through direct phosphorylation in response to DNA damage.
c Abl phosphorylates Mdm2 at tyrosines 276 and 394. Phosphorylation of Mdm2 tyrosine 276 leads to increased levels of nucleolar Mdm2 and increases binding of Mdm2 to its negative regulator, ARF. Thus ARF protects p53 through re localization of Mdm2. Phosphorylation of Mdm2 tyrosine 394 stabilizes p53 and inhibits the negative regulation of Mdm2 on p53 transcriptional and apoptotic activities. An additional c Abl target site at Mdm2 tyrosine 405 has been identified but a physiological role has not been determined. These events support a multi factorial model of Mdm2 regulation based on varied signaling events. 2.3. Phosphorylation of Mdmx after DNA damage As with Mdm2, Mdmx is also phosphorylated at multiple sites in response to DNA damage.
ATM phosphorylation of Mdmx at serine 403 leads to rapid degradation of Mdmx alleviating repression of p53 activity. ATM dependent Chk2 phosphorylation of Mdmx at serine 367 increases binding to the adapter protein 14 3 3, which has been suggested to compete with the de ubiquitinating enzyme HAUSP leading to destabilization of Mdmx. In addition, Mdmx serines 161, 342, 365 and 391 are also phosphorylated in response to DNA damage but their relative contribution to Mdmx regulation is not known. Wang YV and co authors have generated a mouse that harbors a series of three conserved serine to alanine mutations in Mdmx, sites that become phosphorylated in response to DNA damage. The authors report that these mice lack robust Mdmx degradation in response to DNA damage and that this compromises p53 activity.
This result highlights the in vivo importance of these modifications in control of the cellular response to stress. Recently it has been shown that c Abl phosphorylates Mdmx at tyrosines 55 and 99. Phosphorylation of Mdmx at tyrosine 99 inhibits Mdmx p53 complex formation, which frees p53 to activate gene expression. Also, casein kinase 1 alpha has been shown to phosphorylate Mdmx at serine 289 in the acidic domain. Knockdown of CK1 or ionizing radiation leads to the activation of p53 and apoptosis but the molecular mechanism remains to be determined. Thus varied responses to DNA damage have the potenti