p53-family proteins and their regulators: hubs and spokes in tumor suppressionCollavin, L; Lunardi, A; Del Sal, G
doi: 10.1038/cdd.2010.35pmid: 20379196
The tumor suppressor p53 is a central hub in a molecular network controlling cell proliferation and death in response to potentially oncogenic conditions, and a wide array of covalent modifications and protein interactions modulate the nuclear and cytoplasmic activities of p53. The p53 relatives, p73 and p63, are entangled in the same regulatory network, being subject at least in part to the same modifications and interactions that convey signals on p53, and actively contributing to the resulting cellular output. The emerging picture is that of an interconnected pathway, in which all p53-family proteins are involved in the response to oncogenic stress and physiological inputs. Therefore, common and specific interactors of p53-family proteins can have a wide effect on function and dysfunction of this pathway. Many years of research have uncovered an impressive number of p53-interacting proteins, but much less is known about protein interactions of p63 and p73. Yet, many interactors may be shared by multiple p53-family proteins, with similar or different effects. In this study we review shared interactors of p53-family proteins with the aim to encourage research into this field; this knowledge promises to unveil regulatory elements that could be targeted by a new generation of molecules, and allow more efficient use of currently available drugs for cancer treatment.
Reciprocal epigenetic modification of histone H2B occurs in chromatin during apoptosis in vitro and in vivoAjiro, K; Scoltock, A B; Smith, L K; Ashasima, M; Cidlowski, J A
doi: 10.1038/cdd.2009.199pmid: 20057502
Histone H2B phosphorylation at Serine 14 (phosS14) has been proposed as an epigenetic marker of apoptotic cells, whereas acetylation at the adjacent Lysine 15 (acK15) is a property of non-dying cells. We investigated the relationship and the potential regulatory mechanisms between these two epigenetic histone modifications and internucleosomal DNA degradation during apoptosis. Using rat primary thymocytes induced to undergo apoptosis with glucocorticoids we found that H2B phosphorylated at Ser14 was associated with soluble, cleaved DNA in apoptotic nuclei. In contrast acK15 was prevalent in non-apoptotic nuclei and scarce in apoptotic nuclei. This switch between K15 acetylation and S14 phosphorylation on H2B was also observed in apoptotic thymocytes from animals treated in vivo with glucocorticoids and in a rat hepatoma cell line (HTC) induced to die by UV-C or Fas ligand. It is interesting to note that the combined use of a histone deacetylase inhibitor and glucocorticoid suppressed both S14 phosphorylation and internucleosomal DNA degradation without inhibiting apoptosis in thymocytes. Using synthetic peptides and a PKC phosphorylation assay system, we show that the deacetylation of K15 was necessary to allow the S14 phosphorylation. These findings suggest that selective chromatin post-translational modifications are associated with DNA degradation during apoptosis.
Mcl-1 promotes survival of thymocytes by inhibition of Bak in a pathway separate from Bcl-2Dunkle, A; Dzhagalov, I; He, Y-W
doi: 10.1038/cdd.2009.201pmid: 20057504
The antiapoptotic proteins Mcl-1 and Bcl-2 have been shown to be critical in T-cell development and homeostasis, but the precise mechanism by which these proteins function in T cells and other cells of the body is unclear. Potential mechanisms have allowed both for overlapping and unique roles for these proteins because of their abilities to bind different proapoptotic Bcl-2 family members, but it is unclear which of these mechanisms are important in an in vivo context. By generation of various genetic mouse models, we found that Mcl-1-deficient thymocytes die largely by a Bak-specific mechanism. In vivo deletion of Bak rescued the survival and developmental blocks of Mcl-1-deficient thymocytes at the double-negative and single-positive stages. Transgenic overexpression of Bcl-2 and in vivo deletion of Bax or Bim were unable to rescue Mcl-1-deficient thymocytes. Thus, Mcl-1 functions in a unique pathway from Bcl-2 in T lymphocytes, likely because of its specific ability to bind and sequester proapoptotic Bak. Together, these data provide an in vivo model for Mcl-1 activity and present us with a greater understanding of the pathways that promote thymocyte survival.
BUB3 that dissociates from BUB1 activates caspase-independent mitotic death (CIMD)Niikura, Y; Ogi, H; Kikuchi, K; Kitagawa, K
doi: 10.1038/cdd.2009.207pmid: 20057499
The cell death mechanism that prevents aneuploidy caused by a failure of the spindle checkpoint has recently emerged as an important regulatory paradigm. We previously identified a new type of mitotic cell death, termed caspase-independent mitotic death (CIMD), which is induced during early mitosis by partial BUB1 (a spindle checkpoint protein) depletion and defects in kinetochore–microtubule attachment. In this study, we have shown that survived cells that escape CIMD have abnormal nuclei, and we have determined the molecular mechanism by which BUB1 depletion activates CIMD. The BUB3 protein (a BUB1 interactor and a spindle checkpoint protein) interacts with p73 (a homolog of p53), specifically in cells wherein CIMD occurs. The BUB3 protein that is freed from BUB1 associates with p73 on which Y99 is phosphorylated by c-Abl tyrosine kinase, resulting in the activation of CIMD. These results strongly support the hypothesis that CIMD is the cell death mechanism protecting cells from aneuploidy by inducing the death of cells prone to substantial chromosome missegregation.
Nitric oxide repression of Nanog promotes mouse embryonic stem cell differentiationMora-Castilla, S; Tejedo, J R; Hmadcha, A; Cahuana, G M; Martín, F; Soria, B; Bedoya, F J
doi: 10.1038/cdd.2009.204pmid: 20075941
Exposure of mouse embryonic stem (mES) cells to high concentrations of chemical nitric oxide (NO) donors promotes differentiation, but the mechanisms involved in this process at the gene expression level are poorly defined. In this study we report that culture of mES cells in the presence of 0.25–1.0 mM diethylenetriamine nitric oxide adduct (DETA-NO) leads to downregulation of Nanog and Oct4, the two master genes involved in the control of the pluripotent state. This action of NO was also apparent in the human ES cell line, HS 181. The suppressive action of NO on Nanog gene depends on the activation of p53 repressor protein by covalent modifications, such as pSer15, pSer315, pSer392 and acetyl Lys 379. NO-induced repression of Nanog is also associated with binding of trimethylated histone H3 and pSer315 p53 to its promoter region. In addition, exposure to 0.5 mM DETA-NO induces early differentiation events of cells with acquisition of epithelial morphology and expression of markers of definitive endoderm, such as FoxA2, Gata4, Hfn1-β and Sox 17. This phenotype was increased when cells were treated with valproic acid (VPA) for 10 days.
Fas ligand gene expression is directly regulated by stress-inducible heat shock transcription factor-1Bouchier-Hayes, L; McBride, S; van Geelen, C M; Nance, S; Lewis, L K; Pinkoski, M J; Beere, H M
doi: 10.1038/cdd.2010.4pmid: 20150914
Heat shock transcription factor-1 (HSF-1) is the primary stress responsive transcription factor that regulates expression of heat shock proteins (Hsps) in response to elevated temperature. We show that the transcriptional activity of HSF-1 can also directly mediate hyperthermia-induced Fas ligand (FasL) expression in activated T cells. We identify a conserved region within the human FasL promoter spanning from –276 to –236 upstream of the translational start site that contains two 15 bp non-identical adjacent HSF-1-binding sites or heat shock elements (HSEs) separated by 11 bp. Both the distal HSE (HSE1) (extending from −276 to –262) and the proximal HSE (HSE2) (spanning from −250 to –236) consist of two perfect and one imperfect nGAAn pentamers. We show the direct binding of HSF-1 to these elements and that mutation of these sites abrogates the ability of HSF-1 to bind and drive promoter activity. HSF-1 associates with these elements in a cooperative manner to mediate optimal promoter activity. We propose that the ability of HSF-1 to mediate stress-inducible expression of FasL extends its classical function as a regulator of Hsps to encompass a function for this transcription factor in the regulation of immune function and homeostasis.
Association of fission proteins with mitochondrial raft-like domainsCiarlo, L; Manganelli, V; Garofalo, T; Matarrese, P; Tinari, A; Misasi, R; Malorni, W; Sorice, M
doi: 10.1038/cdd.2009.208pmid: 20075943
It was shown that receptor-mediated apoptosis involves a cascade of subcellular events including alterations of mitochondria. Loss of mitochondrial membrane potential that follows death receptor ligation allows the release of apoptogenic factors that result in apoptosis execution. Further important mitochondrial changes have been observed in this regard: mitochondrial remodeling and fission that appear as prerequisites for the occurrence of the cell death program. As it was observed that lipid rafts, glycosphingolipid-enriched structures, can participate in the apoptotic cascade being recruited to the mitochondria under receptor-mediated proapoptotic stimulation, we decided to analyze the possible implication of these microdomains in mitochondrial fission. We found that molecules involved in mitochondrial fission processes are associated with these domains. In particular, although hFis1 was constitutively included in mitochondrial raft-like domains, dynamin-like protein 1 was recruited to these domains on CD95/Fas triggering. Accordingly, the disruption of rafts, for example, by inhibiting ceramide synthase, leads to the impairment of fission molecule recruitment to the mitochondria, reduction of mitochondrial fission and a significant reduction of apoptosis. We hypothesize that under apoptotic stimulation the recruitment of fission-associated molecules to the mitochondrial rafts could have a role in the morphogenetic changes leading to organelle fission.