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Marikki Laiho

Publications and source records attributed to Marikki Laiho.

17 recordsLinked to original sources
PubMed2005

Cellular UV damage responses--functions of tumor suppressor p53.

DNA damage, provoked by ultraviolet (UV) radiation, evokes a cellular damage response composed of activation of stress signaling and DNA checkpoint functions. These are translated to responses of replicative arrest, damage repair, and apoptosis aimed at cellular recovery from the damage. p53 tumor suppressor is a central stress response protein, activated by multiple endogenous and environmental insults, including UV radiation. The significance of p53 in the DNA damage responses has frequently been reviewed in the context of ionizing radiation or other double strand break (DSB)-inducing agents. Despite partly similar patterns, the molecular events following UV radiation are, however, distinct from the responses induced by DSBs and are profoundly coupled with transcriptional stress. These are illustrated, e.g., by the UV damage-specific translocations of Mdm2, promyelocytic leukemia protein, and nucleophosmin and their interactions with p53. In this review, we discuss UV damage-provoked cellular responses and the functions of p53 in damage recovery and cell death.

Animals↗
PubMed2005

FGF-2 blocks TGF-beta1-mediated suppression of Bcl-2 in normal melanocytes.

Normal melanocytes require growth support provided by the adjacent basement membrane. In contrast, nevus cells and melanoma cells survive in the dermis, and in vitro on a soft collagen gel. Transforming growth factor-beta1 (TGF-beta1) produced by melanocytes themselves induces apoptosis in normal melanocytes cultured on collagen gel, an effect that can be counteracted by fibroblast growth factor-2 (FGF-2). The purpose of this study was to investigate the mechanisms by which FGF-2 counteracts the apoptotic signals from TGF-beta1 in melanocytes cultured on collagen gel. We report that FGF-2 did not interfere with the signal transduction from the TGF-beta1 receptors to SMAD2/3 proteins. Instead, TGF-beta1 decreased the level of Bcl-2 in normal melanocytes cultured on collagen gel, and FGF-2 reversed the TGF-beta1-mediated reduction in the level of Bcl-2. In nevus and melanoma cells, TGF-beta1 was unable to induce a decrease in the level of Bcl-2, and treatment with FGF-2 did not cause an increase in the level of Bcl-2 in nevus or melanoma cells. In conclusion, our results suggest that a reduction in the level of the anti-apoptotic Bcl-2 is involved in the execution of apoptosis induced by TGF-beta1 in normal melanocytes cultured on collagen gel and that FGF-2 can prevent TGF-beta1 from causing this reduction.

Apoptosis↗
PubMed2005

Melanoma cell lines are susceptible to histone deacetylase inhibitor TSA provoked cell cycle arrest and apoptosis.

Melanoma is the most aggressive of skin cancers because of its high resistance to currently available therapy. Although melanoma cells often retain wild-type p53 tumour suppressor protein and express it at high levels, the p53 mediated apoptosis pathway is suppressed. Histone deacetylase (HDAC) inhibitors are a promising group of compounds inducing differentiation, growth arrest and apoptosis in tumour cells in preclinical studies. We have studied the cellular effects of trichostatin A (TSA), a HDAC inhibitor, in a panel of melanoma cell lines and its mechanism of action in relation to p53. TSA stabilized wild-type p53, but p53 protein accumulation was overridden by simultaneous downregulation of p53 mRNA leading to a decrease in p53 protein. While growth arrest was induced in all cell lines studied and apoptosis in most (6/7), these cellular effects were independent of the p53 status of the cells. Inhibiting p53 function by a dominant negative p53 (p53(175His)) confirmed that the HDAC inhibitor induced apoptosis was independent of wild-type p53, even though TSA slightly activated p53 in a reporter assay. The results indicate that while the action of TSA is independent of p53, the activation of the apoptosis pathway by the HDAC inhibitors may provide therapeutic approaches for melanoma treatment.

Apoptosis↗
PubMed2004

Myc antagonizes Ras-mediated growth arrest in leukemia cells through the inhibition of the Ras-ERK-p21Cip1 pathway.

Even though RAS usually acts as a dominant transforming oncogene, in primary fibroblasts and some established cell lines Ras inhibits proliferation. This can explain the virtual absence of RAS mutations in some types of tumors, such as chronic myeloid leukemia (CML). We report that in the CML cell line K562 Ras induces p21Cip1 expression through the Raf-MEK-ERK pathway. Because K562 cells are deficient for p15INK4b, p16INK4a, p14ARF, and p53, this would be the main mechanism whereby Ras up-regulates p21 expression in these cells. Accordingly, we also found that Ras suppresses K562 growth by signaling through the Raf-ERK pathway. Because c-Myc and Ras cooperate in cell transformation and c-Myc is up-regulated in CML, we investigated the effect of c-Myc on Ras activity in K562 cells. c-Myc antagonized the induction of p21Cip1 mediated by oncogenic H-, K-, and N-Ras and by constitutively activated Raf and ERK2. Activation of the p21Cip1 promoter by Ras was dependent on Sp1/3 binding sites in K562. However, mutational analysis of the p21 promoter and the use of a Gal4-Sp1 chimeric protein strongly suggest that c-Myc affects Sp1 transcriptional activity but not the binding of Sp1 to the p21 promoter. c-Myc-mediated impairment of Ras activity on p21 expression required a transactivation domain, a DNA binding region, and a Max binding region. Moreover, the effect was independent of Miz1 binding to c-Myc. Consistent with its effect on p21Cip1 expression, c-Myc rescued cell growth inhibition induced by Ras. The data suggest that in particular tumor types, such as those associated with CML, c-Myc contributes to tumorigenesis by inhibiting Ras antiproliferative activity.

Cell Cycle Proteins↗
PubMed2004

Nucleophosmin, HDM2 and p53: players in UV damage incited nucleolar stress response.

p53 tumor suppressor protein acts as a critical monitor preventing survival of cells with irreparable genetic damage. Its levels are tightly controlled by its negative regulator HDM2, and are allowed to rise only during cellular stress. In our recent paper (Kurki, et al. Cancer Cell 2004; 5:465-75) we identify a novel mechanism leading to p53 stabilization following UV damage of the cells. This involves UV damage provoked nucleoplasmic relocalization of a nucleolar protein, nucleophosmin (NPM, B23) and its rapid and transient interactions with both p53 and HDM2. We discuss here implications of recent findings that several p53 pathway proteins interact with NPM and find that its participation in cellular damage responses is limited to transcriptional stress but absent in direct ds DNA breaks. These findings suggest divergence in the routes provoking p53 stability and implicate the nucleolus as a central site participating in transcriptional stress responses.

Cell Nucleus↗
PubMed2004

Nucleolar protein NPM interacts with HDM2 and protects tumor suppressor protein p53 from HDM2-mediated degradation.

Nucleophosmin (NPM, B23) is an abundant nucleolar phosphoprotein involved in ribosome biogenesis, and interacts with tumor suppressor proteins p53 and Rb. Here we show that NPM is a UV damage response protein that undergoes nucleoplasmic redistribution and regulates p53 and HDM2 levels and their interaction. By utilizing RNAi approaches and analyses of endogenous and ectopically expressed proteins, we demonstrate that NPM binds HDM2 and acts as a negative regulator of p53-HDM2 interaction. Viral stress, enforced by expression of Kaposi's sarcoma virus K cyclin, causes NPM redistribution, K cyclin-NPM association, and p53 stabilization by dissociation of HDM2-p53 complexes. The results demonstrate novel associations of HDM2 and K cyclin with NPM and implicate NPM as a crucial controller of p53 through inhibition of HDM2.

Animals↗
PubMed2003

On and off: proteasome and TGF-beta signaling.

Transforming growth factor-beta (TGF-beta) signaling mainly relies on the TGF-beta receptor-Smad pathway. Meanwhile, TGF-beta binding to its receptors initiates the degradation of several key components of its signaling pathway. The degradation of these components, including both positive and negative transducers, is mediated by the ubiquitin-proteasome system. Inhibition of the proteasome activity causes accumulation of these components in the cells and modulates TGF-beta signaling in a time-dependent and gene-specific manner. The accelerated degradation of TGF-beta signaling components via the proteasome system has been found in a number of tumors, indicating that dysregulated proteasomal degradation is a novel pathway how tumor cells silence TGF-beta signaling.

Animals↗
PubMed2003

Cell cycle arrest and apoptosis provoked by UV radiation-induced DNA damage are transcriptionally highly divergent responses.

DNA damage caused by UV radiation initiates cellular recovery mechanisms, which involve activation of DNA damage response pathways, cell cycle arrest and apoptosis. To assess cellular transcriptional responses to UVC-induced DNA damage we compared time course responses of human skin fibroblasts to low and high doses of UVC radiation known to induce a transient cellular replicative arrest or apoptosis, respectively. UVC radiation elicited >3-fold changes in 460 out of 12,000 transcripts and 89% of these represented downregulated transcripts. Only 5% of the regulated genes were common to both low and high doses of radiation. Cells inflicted with a low dose of UVC exhibited transcription profiles demonstrating transient regulation followed by recovery, whereas the responses were persistent after the high dose. A detailed clustering analysis and functional classification of the targets implied regulation of biologically divergent responses and suggested involvement of transcriptional and translational machinery, inflammatory, anti-proliferative and anti-angiogenic responses. The data support the notion that UVC radiation induces prominent, dose-dependent downregulation of transcription. However, the data strongly suggest that transcriptional repression is also target gene selective. Furthermore, the results demonstrate that dose-dependent induction of cell cycle arrest and apoptosis by UVC radiation are transcriptionally highly distinct responses.

Apoptosis↗
PubMed2003

Ski-related novel protein N (SnoN), a negative controller of transforming growth factor-beta signaling, is a prognostic marker in estrogen receptor-positive breast carcinomas.

Transforming growth factor (TGF)-beta arrests the growth of breast epithelial cells, whereas breast cancer cells are highly resistant to its growth restrictive properties. To define causes for the defect in TGF-beta action, we present here the first in vivo analysis of Ski-related novel protein N (SnoN), a negative regulator of TGF-beta signaling, in human breast carcinomas. SnoN expression was analyzed by immunohistochemistry in a tissue microarray of 1122 breast carcinomas and 10 reduction mammoplasties. In the normal breast, SnoN was located predominantly in nuclei of large duct epithelial cells and the cytoplasm of terminal duct epithelial cells. Breast cancers displayed variances in both SnoN expression levels and subcellular localizations. High levels of cytoplasmic SnoN were more often observed in tumors of ductal histological type and associated with adverse prognostic features, such as lack of hormone receptors; high levels of p53, Ki-67, and cyclooxygenase-2; and amplifications of HER-2. High levels of nuclear SnoN were associated with lobular histology and favorable features, including presence of hormone receptors, low expression of p53 and Ki-67, and lack of HER-2 amplifications. Reduced expression of SnoN significantly correlated with longer distant disease-free survival in estrogen receptor-positive patients (P = 0.0027, relative risk = 3.27; 95% confidence interval = 1.44-7.41). The results suggest that the subcellular localization of SnoN may have clinical significance and that reduced expression of SnoN is associated with favorable outcome in estrogen receptor-positive breast cancer.

Adult↗
PubMed2003

Cellular stress and DNA damage invoke temporally distinct Mdm2, p53 and PML complexes and damage-specific nuclear relocalization.

Mdm2 is a nucleoplasmic and nucleolar protein interacting with p53 and alternative reading frame (ARF) tumor suppressor proteins. Here we demonstrate relocalization and novel interactions of Mdm2 with the promyelocytic leukemia (PML) protein following cellular stress and DNA damage. We show that Mdm2 and PML interact directly in vivo and in vitro depending on the Mdm2 RING finger domain and the PML C-terminus, and that Mdm2 is recruited to the PML nuclear bodies by overexpression of PML. Cellular stress and DNA damage caused by UV-radiation, downregulation of the proteasome and arsenic trioxide promoted Mdm2 and PML damage-specific nuclear relocalization and interaction in a p53-independent manner. However, in vitro analyses showed that PML, Mdm2 and p53 form trimeric complexes. UV-radiation caused rapid rearrangements of PML nuclear bodies and promoted PML-p53 and PML-Mdm2 complex formation, coinciding with p53 stabilization and preceding p53-Mdm2 interaction suggesting temporally distinct complexes. The results demonstrate novel associations between Mdm2 and PML and show the capacity of PML to participate in the activation and stabilization of p53 in response to cellular stress through PML interaction with Mdm2.

Animals↗
PubMed2003

p53 and MDM2 are regulated by PI-3-kinases on multiple levels under stress induced by UV radiation and proteasome dysfunction.

p53 is a key stress responsive cellular component. It is negatively regulated by MDM2, which is also its transcriptional target. Here we have studied the involvement of phosphatidylinositol-3-kinases (PI-3-kinase) in the regulation of p53-MDM2 pathway following cellular stress induced by UV damage and proteasomal downregulation. We show that p53 stabilized both by proteasome inhibition and UV damage is transcriptionally active. However, p53 in proteasomally downregulated cells differs from UV-stabilized p53 in its interaction with MDM2, posttranslational modifications and subnuclear localization. It is known that members of PI-3-kinase family are able to directly phosphorylate p53 and MDM2. We show that these kinases regulate p53 accumulation after UV radiation, but accumulation of MDM2 after proteasome inhibition. Both proteins have earlier been shown to translocate into nucleoli after downregulation of the proteasome. We found this effect to be dependent on PI-3-kinase activity but not on any suggested PI-3-kinase phosphorylation site on MDM2. In conclusion, we show here that PI-3-kinases regulate p53-MDM2 pathway on multiple, earlier unknown levels.

Animals↗
PubMed2003

Cell cycle control, DNA damage checkpoints and cancer.

DNA damage checkpoints are essential control points in the cell cycle ensuring effective damage repair. The loss of checkpoint functions leads to loss of genomic integrity and allows accumulation of genetic damage in the daughter cells. Checkpoint deficiency is one of the main causes of DNA aberrations in cancer.

Animals↗
PubMed2002

TGF-beta induced G(1) cell cycle arrest requires the activity of the proteasome pathway. Transforming growth factor.

Transforming growth factor-beta (TGF-beta) induces a potent G(1)/S-phase cell cycle arrest of epithelial cells by inhibiting the activities of cyclin D- and cyclin E-associated kinase complexes. Downregulation of the kinase activities is mediated by induction of cyclin dependent kinase (CDK) inhibitor p15(Ink4b) which blocks CDK4 and CDK6 kinases and leads to binding of p27(Kip1) to CDK2-cyclin E complex. Levels of several of these factors are controlled by the ubiquitin-proteasome pathway. We demonstrate here that proteasomal inhibitors release the cells from TGF-beta imposed G(1)-phase arrest and instigate the entry of the cells into S-phase. Proteasomal inhibitors are shown to specifically increase the activity of the cyclin D-kinase complex by increasing the levels of p27(Kip1) and cyclin D and by maintaining CDK4/6 protein levels leading to phosphorylation of the retinoblastoma protein without increasing cyclin E-associated kinase activity. The results indicate caution in the potential therapeutic use of the proteasome inhibitors due to unscheduled initiation of DNA replication in the presence of a physiological growth inhibitor.

Animals↗
PubMed2002

Proteasomal activity modulates TGF-ss signaling in a gene-specific manner.

Transforming growth factor-beta (TGF-beta) signaling relies on Smad-signaling pathway controlled in part by the proteasome. Here we demonstrate that inhibition of the proteasome function in mink epithelial cells accumulates both positive and negative modulators of TGF-beta signaling, phospho-Smad2 and SnoN. Inhibition of the proteasome led to abrogation of TGF-beta target gene regulation in a gene-specific manner. While regulation of p15Ink4b and myc by TGF-beta are lost, PAI-1 induction, previously shown to occur in a Smad3-dependent manner, was not affected by treatment of the cells with the proteasomal inhibitor MG132. The results suggest that proteasomal activity is required for TGF-beta signaling in a gene-specific manner.

Animals↗
PubMed2002

Redox state of tumor suppressor p53 regulates its sequence-specific DNA binding in DNA-damaged cells by cysteine 277.

Using a bio-oligo pull-down DNA-binding assay we investigated the binding capacity of endogenous, DNA damage-induced p53 in human diploid fibroblasts to several p53-responsive elements (REs) present in p53-regulated genes. During the course of p53 accumulation, we observed a decrease in p53 binding to the GADD45 but not to the p21(WAF1/CIP1) RE. Using mutated GADD45 sequences we show that this change is dependent on the presence of cytosines at position 3 in RE pentamers and on the p53 redox state. Site-directed mutagenesis experiments demonstrated that Cys277 (a residue directly contacting base 3 in a RE pentamer) is critical for differential regulation of GADD45 in DNA-damaged cells. These data represent a novel mechanism for differential affinity of p53 to distinct REs.

Amino Acid Substitution↗