These include specific phosphatases as well as MAPK kinase kinases

re treated for 04h with cycloheximide to inhibit protein synthesis, and lysates were interrogated for the abundance of the ectopically expressed proteins. K129A was indeed less stable than WT, but K129R, despite being almost exclusively cytoplasmic, also turned over more rapidly. Thus we conclude that K129 is important for survivin stability regardless of its Digitoxin subcellular localization. Discussion Acetylation is a post-translational modification implemented by acetyl transferases/deacetylases, of which the best known are histone acetyl-transferases/deacetylases, and a family of nicotinamide adenine dinucleotide C-dependent deacetylases called Sirtuins.20,21 Activation of many genes is regulated by acetylation, but transcription is only one of many mechanisms regulated by reversible acetylation, and the 2 most relevant here are cell proliferation and apoptosis. For example, depletion of the ubiquitous and highly conserved HDAC3 prevents proper construction of the mitotic spindle PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19837048 and weakens kinetochore-microtubule attachment in prometaphase cells.22 Furthermore many mitotic proteins, including tubulin, BubR1,23 APC, shuogoshin-2,24 CPPs aurora-B kinase25 and survivin6 are acetylated. 1744 Cell Cycle Volume 14 Issue 11 Using acetylation mimetics, Wang et al., demonstrated that survivin acetylation at K129 influences its subcellular localization in interphase cells.6 More recently the same group has suggested that monitoring the localization of acetylated survivin has diagnostic potential in breast cancer subtyping.26,27 Using a similar mutagenic strategy to them, we investigated whether this PTM impacts on survivin function during mitotic exit. Our data clearly show that cells expressing the acetyl-mimetic, K129A, do not heed the “wait anaphase” signal, but rush through anaphase in the presence of maloriented chromosomes, resulting in aberrant division, often producing 3 aneuploid cells or binucleation. Thus persistent acetylation of survivin at K129 during mitosis compromises SAC and consequently cytokinesis fails, showing that if acetylated at this site, deacetylation has to occur to ensure successful segregation of the chromosomes and division. We, like others, have demonstrated that survivin is required to ensure a robust SAC mounted by the tension sensing protein, BubR1.2,28 As K129A cells exit mitosis in the presence of maloriented chromosomes, this observation was extended; it showed that persistent acetylation of survivin at K129 compromises BubR1 sensing. In support of our mutagenesis data, we noted that sustained global acetylation by treatment with the HDAC inhibitor, TSA, also led to precocious entry into anaphase and cytokinesis failure. These data provide substantial evidence that the acetylation status of survivin is critical for genomic stability during mitosis. However, we are mindful that acetylation of other mitotic proteins including aurora-B25 and BubR1 itself,23 as well as certain cytokinetic proteins, may contribute to and exacerbate the mitotic and cytokinetic abnormalities seen in the chemically-induced acetylated state. In addition to mitotic defects we found that mimicking acetylation of survivin leads to some relocation to the nucleus, which concurs with Wang et al.,.6 By way of a mechanistic explanation, it has been proposed that survivin is acetylated in a CBP-dependent manner and that deacetylation by HDAC626 aids survivin interaction with CRM1/exportin to alter its export from the nucleus.6 This seems unusual