Regulation of p53 activity by its interaction with homeodomain-interacting protein kinase-2Hofmann, Thomas G.; Möller, Andreas; Sirma, Hüseyin; Zentgraf, Hanswalter; Taya, Yoichi; Dröge, Wulf; Will, Hans; Schmitz, M. Lienhard
doi: 10.1038/ncb715pmid: 11740489
Transcriptional activity of p53, a central regulatory switch in a network controlling cell proliferation and apoptosis, is modulated by protein stability and post-translational modifications including phosphorylation and acetylation. Here we demonstrate that the human serine/threonine kinase homeodomain-interacting protein kinase-2 (HIPK2) colocalizes and interacts with p53 and CREB-binding protein (CBP) within promyelocytic leukaemia (PML) nuclear bodies. HIPK2 is activated by ultraviolet (UV) radiation and selectively phosphorylates p53 at Ser 46, thus facilitating the CBP-mediated acetylation of p53 at Lys 382, and promoting p53-dependent gene expression. Accordingly, the kinase function of HIPK2 mediates the increased expression of p53 target genes, which results in growth arrest and the enhancement of UV-induced apoptosis. Interference with HIPK2 expression by antisense oligonucleotides impairs UV-induced apoptosis. Our results imply that HIPK2 is a novel regulator of p53 effector functions involved in cell growth, proliferation and apoptosis.
The planar cell-polarity gene stbm regulates cell behaviour and cell fate in vertebrate embryosPark, Maiyon; Moon, Randall T.
doi: 10.1038/ncb716pmid: 11780127
The gene strabismus (stbm)/Van Gogh (Vang) functions in the planar cell-polarity pathway in Drosophila. As the existence of such a pathway in vertebrates has not been firmly established, we investigated the functions and signalling activities encoded by stbm in vertebrate embryos. In regard to cell fate, inhibition of Stbm function in zebrafish embryos leads to reduction of anterior neural markers, whereas gain of function leads to a rise in the levels of these markers. In regard to cell behaviour, both gain-of-function and loss-of-function assays reveal a role for Stbm in mediating cell movements during gastrulation. Mechanistically, Stbm inhibits Wnt-mediated activation of β-catenin-dependent transcription while promoting phosphorylation of c-Jun- and AP-1-dependent transcription. This complex effect on intracellular signalling pathways probably involves dishevelled (dsh), as Stbm was found to interact with the Dsh protein, and as Dsh is known to function in both planar cell-polarity and β-catenin pathways in Drosophila.
Interleukin-12 suppresses ultraviolet radiation-induced apoptosis by inducing DNA repairSchwarz, Agatha; Ständer, Sonja; Berneburg, Mark; Böhm, Markus; Kulms, Dagmar; van Steeg, Harry; Grosse-Heitmeyer, Karin; Krutmann, Jean; Schwarz, Thomas
doi: 10.1038/ncb717pmid: 11780128
Induction of apoptosis of keratinocytes by ultraviolet (UV) radiation is a protective phenomenon relevant in limiting the survival of cells with irreparable DNA damage. Changes in UV-induced apoptosis may therefore have significant impact on photocarcinogenesis. We have found that the immunomodulatory cytokine IL-12 suppresses UV-mediated apoptosis of keratinocytes both in vitro and in vivo. IL-12 caused a remarkable reduction in UV-specific DNA lesions which was due to induction of DNA repair. In accordance with this, IL-12 induced the expression of particular components of the nucleotide-excision repair complex. Our results show that cytokines can protect cells from apoptosis induced by DNA-damaging UV radiation by inducing DNA repair, and that nucleotide-excision repair can be manipulated by cytokines.
Yeast formins regulate cell polarity by controlling the assembly of actin cablesSagot, Isabelle; Klee, Saskia K.; Pellman, David
doi: 10.1038/ncb719pmid: 11740491
Formins are conserved Rho-GTPase effectors that communicate Rho-GTPase signals to the cytoskeleton. We found that formins were required for the assembly of one of the three budding yeast actin structures: polarized arrays of actin cables. A dominant-active formin induced the assembly of actin cables. The activation and localization of the formin Bni1p required components of the polarisome complex. These findings potentially define the cellular function of formins in budding yeast and explain their involvement in the generation of cell polarity. A requirement for formins in constructing specific actin structures might be the basis for the diverse activities of formins in development.
TGF-β induces apoptosis through Smad-mediated expression of DAP-kinaseJang, Chuan-Wei; Chen, Chun-Hau; Chen, Chun-Chieh; Chen, Jia-yun; Su, Yi-Hsien; Chen, Ruey-Hwa
doi: 10.1038/ncb731pmid: 11740493
Transforming growth factor-β (TGF-β) and TGF-β-related factors induce apoptosis in a variety of tissues; however, the mechanism underlying this induction is largely unknown. Here, we demonstrate that TGF-β induces the expression of the death-associated protein kinase (DAP-kinase) as an immediate early response in cells that undergo apoptosis in response to TGF-β. DAP-kinase is a positive mediator of apoptosis induced by certain cytokines and oncogenes. We show that the DAP-kinase promoter is activated by TGF-β through the action of Smad2, Smad3 and Smad4. Overexpression of DAP-kinase triggers apoptosis in the absence of TGF-β, whereas inhibition of DAP-kinase activity protects cells from TGF-β-induced apoptosis, blocks TGF-β-induced release of cytochrome c from mitochondria and prevents TGF-β-induced dissipation of the mitochondrial membrane potential. Our findings indicate that DAP-kinase mediates TGF-β-dependent apoptosis by linking Smads to mitochondrial-based pro-apoptotic events.
The gated gait of the processive molecular motor, myosin VVeigel, Claudia; Wang, Fei; Bartoo, Marc L.; Sellers, James R.; Molloy, Justin E.
doi: 10.1038/ncb732pmid: 11740494
Class V myosins are actin-based molecular motors involved in vesicular and organellar transport. Single myosin V molecules move processively along F-actin, taking several 36-nm steps for each diffusional encounter. Here we have measured the mechanical interactions between mouse brain myosin V and rabbit skeletal F-actin. The working stroke produced by a myosin V head is ∼25 nm, consisting of two separate mechanical phases (20 + 5 nm). We show that there are preferred myosin binding positions (target zones) every 36 nm along the actin filament, and propose that the 36-nm steps of the double-headed motor are a combination of the working stroke (25 nm) of the bound head and a biased, thermally driven diffusive movement (11 nm) of the free head onto the next target zone. The second phase of the working stroke (5 nm) acts as a gate — like an escapement in a clock, coordinating the ATPase cycles of the two myosin V heads. This mechanism increases processivity and enables a single myosin V molecule to travel distances of several hundred nanometres along the actin filament.
The exocyst is a Ral effector complexMoskalenko, Serge; Henry, Dale O.; Rosse, Carine; Mirey, Gladys; Camonis, Jacques H.; White, Michael A.
doi: 10.1038/ncb728pmid: 11740492
Delivery of cytoplasmic vesicles to discrete plasma-membrane domains is critical for establishing and maintaining cell polarity, neurite differentiation and regulated exocytosis. The exocyst is a multisubunit complex required for vectorial targeting of a subset of secretory vesicles. Mechanisms that regulate the activity of this complex in mammals are unknown. Here we show that Sec5, an integral component of the exocyst, is a direct target for activated Ral GTPases. Ral GTPases regulate targeting of basolateral proteins in epithelial cells, secretagogue-dependent exocytosis in neuroendocrine cells and assembly of exocyst complexes. These observations define Ral GTPases as critical regulators of vesicle trafficking.
The exocyst complex binds the small GTPase RalA to mediate filopodia formationSugihara, Kazuhiro; Asano, Shiro; Tanaka, Kenichi; Iwamatsu, Akihiro; Okawa, Katsuya; Ohta, Yasutaka
doi: 10.1038/ncb720pmid: 11744922
The Ras-related small GTPase RalA is involved in controlling actin cytoskeletal remodelling and vesicle transport in mammalian cells
1,2
. We identified the mammalian homologue of Sec5, a subunit of the exocyst complex determining yeast cell polarity, as a specific binding partner for GTP-ligated RalA. Inhibition of RalA binding to Sec5 prevents filopod production by tumor necrosis factor-α (TNF-α) and interleukin-1 (IL-1) and by activated forms of RalA and Cdc42, signalling intermediates downstream of these inflammatory cytokines. We propose that the RalA–exocyst complex interaction integrates the secretory and cytoskeletal pathways.