Isolation and characterization of p19INK4d, a p16-related inhibitor specific to CDK6 and CDK4

The E2F4/p130 Repressor Complex Cooperates with Oncogenic ΔNp73α To Inhibit Gene Expression in Human Papillomavirus 38 E6/E7-Transformed Keratinocytes and in Cancer Cells

Tumor suppressor p53 and its related proteins, p63 and p73, can be synthesized as multiple isoforms lacking part of the N- or C-terminal regions. Specifically, high expression of the ΔNp73α isoform is notoriously associated with various human malignancies characterized by poor prognosis. This isoform is also accumulated by oncogenic viruses, such as Epstein-Barr virus (EBV), as well as genus beta human papillomaviruses (HPV) that appear to be involved in carcinogenesis. To gain additional insight into ΔNp73α mechanisms, we have performed proteomics analyses using human keratinocytes transformed by the E6 and E7 proteins of the beta-HPV type 38 virus as an experimental model (38HK). We find that ΔNp73α associates with the E2F4/p130 repressor complex through a direct interaction with E2F4. This interaction is favored by the N-terminal truncation of p73 characteristic of ΔNp73 isoforms. Moreover, it is independent of the C-terminal splicing status, suggesting that it could represent a general feature of ΔNp73 isoforms (α, β, γ, δ, ε, ζ, θ, η, and η1). We show that the ΔNp73α-E2F4/p130 complex inhibits the expression of specific genes, including genes encoding for negative regulators of proliferation, both in 38HK and in HPV-negative cancer-derived cell lines. Such genes are not inhibited by E2F4/p130 in primary keratinocytes lacking ΔNp73α, indicating that the interaction with ΔNp73α rewires the E2F4 transcriptional program. In conclusion, we have identified and characterized a novel transcriptional regulatory complex with potential implications in oncogenesis. IMPORTANCE The TP53 gene is mutated in about 50% of human cancers. In contrast, the TP63 and TP73 genes are rarely mutated but rather expressed as ΔNp63 and ΔNp73 isoforms in a wide range of malignancies, where they act as p53 antagonists. Accumulation of ΔNp63 and ΔNp73, which is associated with chemoresistance, can result from infection by oncogenic viruses such as EBV or HPV. Our study focuses on the highly carcinogenic ΔNp73α isoform and uses a viral model of cellular transformation. We unveil a physical interaction between ΔNp73α and the E2F4/p130 complex involved in cell cycle control, which rewires the E2F4/p130 transcriptional program. Our work shows that ΔNp73 isoforms can establish interactions with proteins that do not bind to the TAp73α tumor suppressor. This situation is analogous to the gain-of-function interactions of p53 mutants supporting cellular proliferation.

Cyclin-dependent kinase inhibitors in malignant hematopoiesis

The cell-cycle is a tightly orchestrated process where sequential steps guarantee cellular growth linked to a correct DNA replication. The entire cell division is controlled by cyclin-dependent kinases (CDKs). CDK activation is balanced by the activating cyclins and CDK inhibitors whose correct expression, accumulation and degradation schedule the time-flow through the cell cycle phases. Dysregulation of the cell cycle regulatory proteins causes the loss of a controlled cell division and is inevitably linked to neoplastic transformation. Due to their function as cell-cycle brakes, CDK inhibitors are considered as tumor suppressors. The CDK inhibitors p16^INK4a and p15^INK4b are among the most frequently altered genes in cancer, including hematopoietic malignancies. Aberrant cell cycle regulation in hematopoietic stem cells (HSCs) bears severe consequences on hematopoiesis and provokes hematological disorders with a broad array of symptoms. In this review, we focus on the importance and prevalence of deregulated CDK inhibitors in hematological malignancies.

Folding and Stability of Ankyrin Repeats Control Biological Protein Function

Ankyrin repeat proteins are found in all three kingdoms of life. Fundamentally, these proteins are involved in protein-protein interaction in order to activate or suppress biological processes. The basic architecture of these proteins comprises repeating modules forming elongated structures. Due to the lack of long-range interactions, a graded stability among the repeats is the generic properties of this protein family determining both protein folding and biological function. Protein folding intermediates were frequently found to be key for the biological functions of repeat proteins. In this review, we discuss most recent findings addressing this close relation for ankyrin repeat proteins including DARPins, Notch receptor ankyrin repeat domain, IκBα inhibitor of NFκB, and CDK inhibitor p19^INK4d. The role of local folding and unfolding and gradual stability of individual repeats will be discussed during protein folding, protein-protein interactions, and post-translational modifications. The conformational changes of these repeats function as molecular switches for biological regulation, a versatile property for modern drug discovery.

p19INK4d inhibits proliferation and enhances imatinib efficacy through BCR-ABL signaling pathway in chronic myeloid leukemia

Chronic myeloid leukemia (CML) is a kind of myeloproliferative disorder caused by a constitutively active BCR-ABL tyrosine kinase. Tyrosine kinase inhibitors (TKIs), imatinib and its derivatives, have achieved great progress in the treatment of CML. However, many CML patients do not respond to TKIs alone. p19^INK4d, a cyclin-dependent kinase inhibitor, plays important roles in proliferation, DNA damage repair, apoptosis and cell differentiation, but its role in CML is unknown. Herein, we found that the expression of p19^INK4d in CML patients was significantly lower than that in healthy controls. p19^INK4d overexpression inhibits cell proliferation through cell cycle arrest, and cooperates with imatinib to inhibit CML more effectively in vitro and in vivo. Mechanistically, p19^INK4d decreased the expression of BCR-ABL and its downstream molecules p-Mek1/2, moreover, the expression of Gli-1, c-myc, MUC1, Shh and TC48 also reduced significantly. Collectively, p19^INK4d inhibits proliferation and enhances imatinib efficacy in the treatment of CML. These findings maybe have implications for developing potential targets to increase imatinib sensitivity for CML.

Effects of aflatoxin B1 on the cell cycle distribution of splenocytes in chickens

The purpose of the present study was to evaluate effects of aflatoxin B1 (AFB1) on the cell cycle and proliferation of splenic cells in chickens. A total of 144 one-day-old Cobb male chickens were randomly divided into 2 equal groups of 72 each and were fed on diets as follows: a control diet and a 0.6 mg/kg AFB1 diet for 21 days. The AFB1 diet reduced body weight, absolute weight and relative weight of the spleen in broilers. Histopathological lesions in AFB1 groups were characterized as slight congestion in red pulp and lymphocytic depletion in white pulp. Compared with the control group, the expression levels of ataxia-telangiectasia mutated (ATM), cyclin E1, cyclin-dependent kinases 6 (CDK6), CDK2, p53, p21 and cyclin B3 mRNA were significantly increased, while the mRNA expression levels of cyclin D1, cdc2 (CDK1), p16, p15 were significantly decreased in the AFB1 groups. Significantly decreased proliferating cell nuclear antigen (PCNA) expression and arrested G0G1 phases of the cell cycle were also seen in the AFB1 groups. In conclusion, dietary AFB1 could induce cell cycle blockage at G0G1 phase and impair the immune function of the spleen. Cyclin D1/CDK6 complex, which inhibits the activin/nodal signaling pathway, might play a significant role in the cell cycle arrest induced by AFB1.

BOK promotes chemical-induced hepatocarcinogenesis in mice

BCL-2-related ovarian killer (BOK) is a conserved and widely expressed BCL-2 family member with sequence homology to pro-apoptotic BAX and BAK, but with poorly understood pathophysiological function. Since several members of the BCL-2 family are critically involved in the regulation of hepatocellular apoptosis and carcinogenesis we aimed to establish whether loss of BOK affects diethylnitrosamine (DEN)-induced hepatocarcinogenesis in mice. Short-term exposure to DEN lead to upregulation of BOK mRNA and protein in the liver. Of note, induction of CHOP and the pro-apoptotic BH3-only proteins PUMA and BIM by DEN was strongly reduced in the absence of BOK. Accordingly, Bok^-/- mice were significantly protected from DEN-induced acute hepatocellular apoptosis and associated inflammation. As a consequence, Bok^-/- animals were partially protected against chemical-induced hepatocarcinogenesis showing fewer and, surprisingly, also smaller tumors than WT controls. Gene expression profiling revealed that downregulation of BOK results in upregulation of genes involved in cell cycle arrest. Bok^-/- hepatocellular carcinoma (HCC) displayed higher expression levels of the cyclin kinase inhibitors p19^INK4d and p21^cip1. Accordingly, hepatocellular carcinoma in Bok^-/- animals, BOK-deficient human HCC cell lines, as well as non-transformed cells, showed significantly less proliferation than BOK-proficient controls. We conclude that BOK is induced by DEN, contributes to DEN-induced hepatocellular apoptosis and resulting hepatocarcinogenesis. In line with its previously reported predominant localization at the endoplasmic reticulum, our findings support a role of BOK that links the cell cycle and cell death machineries upstream of mitochondrial damage.

Targeting CDK6 in cancer: State of the art and new insights

Cyclin-dependent kinase 6 (CDK6) plays a vital role in regulating the progression of the cell cycle. More recently, CDK6 has also been shown to have a transcriptional role in tumor angiogenesis. Up-regulated CDK6 activity is associated with the development of several types of cancers. While CDK6 is over-expressed in cancer cells, it has a low detectable level in non-cancerous cells and CDK6-null mice develop normally, suggesting a specific oncogenic role of CDK6, and that its inhibition may represent an ideal mechanism-based and low toxic therapeutic strategy in cancer treatment. Identification of selective small molecule inhibitors of CDK6 is thus needed for drug development. Herein, we review the latest understandings of the biological regulation and oncogenic roles of CDK6. The potential clinical relevance of CDK6 inhibition, the progress in the development of small-molecule CDK6 inhibitors and the rational design of potential selective CDK6 inhibitors are also discussed.

Canine Mammary Carcinomas: A Comparative Analysis of Altered Gene Expression

Breast cancer represents the second most frequent neoplasm in humans and sexually intact female dogs after lung and skin cancers, respectively. Many similar features in human and dog cancers including, spontaneous development, clinical presentation, tumor heterogeneity, disease progression and response to conventional therapies have supported development of this comparative model as an alternative to mice. The highly conserved similarities between canine and human genomes are also key to this comparative analysis, especially when compared to the murine genome. Studies with canine mammary tumor (CMT) models have shown a strong genetic correlation with their human counterparts, particularly in terms of altered expression profiles of cell cycle regulatory genes, tumor suppressor and oncogenes and also a large group of non-coding RNAs or microRNAs (miRNAs). Because CMTs are considered predictive intermediate models for human breast cancer, similarities in genetic alterations and cancer predisposition between humans and dogs have raised further interest. Many cancer-associated genetic defects critical to mammary tumor development and oncogenic determinants of metastasis have been reported and appear to be similar in both species. Comparative analysis of deregulated gene sets or cancer signaling pathways has shown that a significant proportion of orthologous genes are comparably up- or down-regulated in both human and dog breast tumors. Particularly, a group of cell cycle regulators called cyclin-dependent kinase inhibitors (CKIs) acting as potent tumor suppressors are frequently defective in CMTs. Interestingly, comparative analysis of coding sequences has also shown that these genes are highly conserved in mammals in terms of their evolutionary divergence from a common ancestor. Moreover, co-deletion and/or homozygous loss of the INK4A/ARF/INK4B (CDKN2A/B) locus, encoding three members of the CKI tumor suppressor gene families (p16/INK4A, p14ARF and p15/INK4B), in many human and dog cancers including mammary carcinomas, suggested their important conserved genetic order and localization in orthologous chromosomal regions. miRNAs, as powerful post-transcriptional regulators of most of the cancer-associated genes, have not been well evaluated to date in animal cancer models. Comprehensive expression profiles of miRNAs in CMTs have revealed their altered regulation showing a strong correlation with those found in human breast cancers. These genetic correlations between human and dog mammary cancers will greatly advance our understanding of regulatory mechanisms involving many critical cancer-associated genes that promote neoplasia and contribute to the promising development of future therapeutics.

Regulation of T cell differentiation and alloimmunity by the cyclin-dependent kinase inhibitor p18ink4c

Cellular proliferation in response to mitogenic stimuli is negatively regulated by the Cip/Kip and the Ink4 families of cyclin-dependent kinase (CDK) inhibitors. Several of these proteins are elevated in anergic T cells, suggesting a potential role in the induction or maintenance of tolerance. Our previous studies showed that p27kip1 is required for the induction of T cell anergy and transplantation tolerance by costimulatory blockade, but a role for Ink4 proteins in these processes has not been established. Here we show that CD4+ T cells from mice genetically deficient for p18ink4c divide more rapidly than wild-type cells in response to antigenic, costimulatory and growth factor signals. However, this gain of proliferative function was accompanied by a moderate increase in the rate of cell death, and was accompanied by an overall defect in the generation of alloreactive IFNγ-producing effector cells. Consistent with this, p18ink4c-deficient T cells were unable to induce graft-vs-host disease in vivo, and p18ink4c deficiency cooperated with costimulatory blockade to significantly increase the survival of fully mismatched allografts in a cardiac transplantation model. While both p18ink4c and p27kip1 act to restrict T cell proliferation, p18ink4c exerts an opposite effect from p27kip1 on alloimmunity and organ transplant rejection, most likely by sustaining T cell survival and the development of effector function. Our studies point to additional important links between the cell cycle machinery and the processes of T cell differentiation, survival and tolerance.

p19(INK4d) mRNA and protein expression as new prognostic factors in ovarian cancer patients

p19(INK4d) (CDKN2D) is a negative regulator of the cell cycle. Little is known of its role in cancer development and prognosis. We aimed to evaluate the clinical significance of p19(INK4d) expression in ovarian carcinomas with respect to the TP53 accumulation status, as well as the frequency of CDKN2D mutations. p19(INK4d) and TP53 expression was evaluated immunohistochemically in 445 ovarian carcinomas: 246 patients were treated with platinum-cyclophosphamide (PC/PAC), while 199 were treated with taxane-platinum agents (TP). CDKN2D gene expression (mRNA) was examined in 106 carcinomas, while CDKN2D mutations in 68 tumors. Uni- and multivariate statistical analyses (logistic regression and the Cox proportional hazards model) were performed for patient groups divided according to the chemotherapeutic regimen administered, and in subgroups with and without TP53 accumulation. High p19(INK4d) expression increased the risk of death, but only in patients with the TP53-negative carcinomas (HR 1.61, P = 0.049 for PC/PAC-treated patients, HR 2.00, P = 0.015 for TP-treated patients). This result was confirmed by the mRNA analysis (HR 4.24, P = 0.001 for TP-treated group). High p19(INK4d) protein expression associated with adverse clinicopathological factors. We found no alterations in the CDKN2D gene; the c.90C>G (p.R30R; rs1968445) polymorphism was detected in 10% of tumors. Our results suggest that p19(INK4d) expression is a poor prognostic factor in ovarian cancer patients. Analyses of tumor groups according to the TP53 accumulation status facilitate the identification of cancer biomarkers.

Signaling through cyclin D-dependent kinases

Research over the past quarter century has identified cyclin D-dependent kinases, CDK4 and CDK6, as the major oncogenic drivers among members of the CDK superfamily. CDK4/6 are rendered hyperactive in the majority of human cancers through a multitude of genomic alterations. Sustained activation of these protein kinases provides cancer cells with the power to enter the cell cycle continuously by triggering G1-S-phase transitions and dramatically shortening the duration of the G1 phase. It has also become clear, however, that CDK4/6 effectively counter cancer cell-intrinsic tumor suppression mechanisms, senescence and apoptosis, which must be overcome during cell transformation and kept at bay throughout all stages of tumorigenesis. As a central 'node' in cellular signaling networks, cyclin D-dependent kinases sense a plethora of mitogenic signals to orchestrate specific transcriptional programs. As the complexity of the cellular signaling network regulated by these oncogenic kinases unfolds, much remains to be learned about its architecture, its dynamics and the consequences of its perturbation.

IL-1 and EGF regulate expression of genes important in inflammation and cancer

This review focuses on the mechanisms by which the expression of specific genes is regulated by two proteins that are important in inflammation and cancer, namely the pro-inflammatory cytokine interleukin (IL)-1β and epidermal growth factor (EGF). In the review the receptors that recognize factors that cause inflammation are described with main focus on the receptors associated with activation of IL-1β. The function of IL-1β and pathways leading to activation of transcription factors, particularly NFκB and Elk-1 are analyzed. Then the mechanisms of EGF action, with particular emphasis of the activation of Elk-1 are illustrated. The link between aberrant signaling of EGF receptor family members and cancer development is explained. The relationship between inflammation and tumorigenesis is discussed.

CDK4 inhibition restores G(1)-S arrest in MYCN-amplified neuroblastoma cells in the context of doxorubicin-induced DNA damage

Relapse with drug-resistant disease is the main cause of death in MYCN-amplified neuroblastoma patients. MYCN-amplified neuroblastoma cells in vitro are characterized by a failure to arrest at the G(1)-S checkpoint after irradiation- or drug-induced DNA damage. We show that several MYCN-amplified cell lines harbor additional chromosomal aberrations targeting p53 and/or pRB pathway components, including CDK4/CCND1/MDM2 amplifications, p16INK4A/p14ARF deletions or TP53 mutations. Cells with these additional aberrations undergo significantly lower levels of cell death after doxorubicin treatment compared with MYCN-amplified cells, with no additional mutations in these pathways. In MYCN-amplified cells CDK4 expression is elevated, increasing the competition between CDK4 and CDK2 for binding p21. This results in insufficient p21 to inhibit CDK2, leading to high CDK4 and CDK2 kinase activity upon doxorubicin treatment. CDK4 inhibition by siRNAs, selective small compounds or p19(INK4D) overexpression partly restored G(1)-S arrest, delayed S-phase progression and reduced cell viability upon doxorubicin treatment. Our results suggest a specific function of p19(INK4D), but not p16(INK4A), in sensitizing MYCN-amplified cells with a functional p53 pathway to doxorubicin-induced cell death. In summary, the CDK4/cyclin D-pRB axis is altered in MYCN-amplified cells to evade a G(1)-S arrest after doxorubicin-induced DNA damage. Additional chromosomal aberrations affecting the p53-p21 and CDK4-pRB axes compound the effects of MYCN on the G(1) checkpoint and reduce sensitivity to cell death after doxorubicin treatment. CDK4 inhibition partly restores G(1)-S arrest and sensitizes cells to doxorubicin-mediated cell death in MYCN-amplified cells with an intact p53 pathway.

Cell cycle regulation during proliferation and differentiation of mammalian muscle precursor cells

Proliferation and differentiation of muscle precursor cells are intensively studied not only in the developing mouse embryo but also using models of skeletal muscle regeneration or analyzing in vitro cultured cells. These analyses allowed to show the universality of the cell cycle regulation and also uncovered tissue-specific interplay between major cell cycle regulators and factors crucial for the myogenic differentiation. Examination of the events accompanying proliferation and differentiation leading to the formation of functional skeletal muscle fibers allows understanding the molecular basis not only of myogenesis but also of skeletal muscle regeneration. This chapter presents the basis of the cell cycle regulation in proliferating and differentiating muscle precursor cells during development and after muscle injury. It focuses at major cell cycle regulators, myogenic factors, and extracellular environment impacting on the skeletal muscle.

Laforin negatively regulates cell cycle progression through glycogen synthase kinase 3beta-dependent mechanisms

Glycogen synthase kinase 3beta (GSK-3beta) represses cell cycle progression by directly phosphorylating cyclin D1 and indirectly regulating cyclin D1 transcription by inhibiting Wnt signaling. Recently, we reported that the Epm2a-encoded laforin is a GSK-3beta phosphatase and a tumor suppressor. The cellular mechanism for its tumor suppression remains unknown. Using ex vivo thymocytes and primary embryonic fibroblasts from Epm2a(-/-) mice, we show here a general function of laforin in the cell cycle regulation and repression of cyclin D1 expression. Moreover, targeted mutation of Epm2a increased the phosphorylation of Ser9 on GSK-3beta while having no effect on the phosphorylation of Ser21 on GSK-3alpha. In the GSK-3beta(+/+) but not the GSK-3beta(-/-) cells, Epm2a small interfering RNA significantly enhanced cell growth. Consistent with an increased level of cyclin D1, the phosphorylation of retinoblastoma protein (Rb) and the levels of Rb-E2F-regulated genes cyclin A, cyclin E, MCM3, and PCNA are also elevated. Inhibitors of GSK-3beta selectively increased the cell growth of Epm2a(+/+) but not of Epm2a(-/-) cells. Taken together, our data demonstrate that laforin is a selective phosphatase for GSK-3beta and regulates cell cycle progression by GSK-3beta-dependent mechanisms. These data provide a cellular basis for the tumor suppression activity of laforin.

P19INK4D links endomitotic arrest and megakaryocyte maturation and is regulated by AML-1

The molecular mechanisms that regulate megakaryocyte (MK) ploidization are poorly understood. Using MK differentiation from primary human CD34(+) cells, we observed that p19(INK4D) expression was increased both at the mRNA and protein levels during ploidization. p19(INK4D) knockdown led to a moderate increase (31.7% +/- 5%) in the mean ploidy of MKs suggesting a role of p19(INK4D) in the endomitotic arrest. This increase in ploidy was associated with a decrease in the more mature MK population (CD41(high)CD42(high)) at day 9 of culture, which was related to a delay in differentiation. Inversely, p19(INK4D) overexpression in CD34(+) cells resulted in a decrease in mean ploidy level associated with an increase in CD41 and CD42 expression in each ploidy class. Confirming these in vitro results, bone marrow MKs from p19(INK4D) KO mice exhibited an increase in mean ploidy level from 18.7N (+/- 0.58N) to 52.7N (+/- 12.3N). Chromatin immunoprecipitation assays performed in human MKs revealed that AML-1 binds in vivo the p19(INK4D) promoter. Moreover, AML-1 inhibition led to the p19(INK4D) down-regulation in human MKs. These results may explain the molecular link at the transcriptional level between the arrest of endomitosis and the acceleration of MK differentiation.

A CDKN2A mutation in familial melanoma that abrogates binding of p16INK4a to CDK4 but not CDK6

The CDKN2A locus encodes two distinct proteins, p16INK4a and p14ARF, both of which are implicated in replicative senescence and tumor suppression in different contexts. Here, we describe the characterization of a novel strain of human diploid fibroblasts (designated Milan HDFs) from an individual who is homozygous for the R24P mutation in p16INK4a. As this mutation occurs in the first exon of INK4a (exon 1alpha), it has no effect on the primary sequence of p14(ARF). Based on both in vitro and in vivo analyses, the R24P variant is specifically defective for binding to CDK4 but remains able to associate with CDK6. Nevertheless, Milan HDFs behave as if they are p16INK4a deficient, in terms of sensitivity to spontaneous and oncogene-induced senescence, and the R24P variant has little effect on proliferation when ectopically expressed in normal fibroblasts. It can, however, impair the proliferation of U20S cells, presumably because they express more CDK6 than primary fibroblasts. These observations suggest that CDK4 and CDK6 are not functionally redundant and underscore the importance of CDK4 in the development of melanoma.

p19Ink4d and p18Ink4c cyclin-dependent kinase inhibitors in the male reproductive axis

The loss of the cyclin-dependent kinase inhibitors (CKIs) p18(Ink4c) and p19(Ink4d) leads to male reproductive defects (Franklin et al., 1998. Genes Dev 12: 2899-2911; Zindy et al., 2000. Mol Cell Biol 20: 372-378; Zindy et al., 2001. Mol Cell Biol 21: 3244-3255). In order to assess whether these inhibitors directly or indirectly affect male germ cell differentiation, we examined the expression of p18(Ink4c) and p19(Ink4d) in spermatogenic and supporting cells in the testis and in pituitary gonadotropes. Both p18(Ink4c) and p19(Ink4d) are most abundant in the testis after 18 days of age and are expressed in purified populations of spermatogenic and testicular somatic cells. Different p18(Ink4c) mRNAs are expressed in isolated spermatogenic and Leydig cells. Spermatogenic cells also express a novel p19(Ink4d) transcript that is distinct from the smaller transcript expressed in Sertoli cells, Leydig cells and in other tissues. Immunohistochemistry detected significant levels of p19(Ink4d) in preleptotene spermatocytes, pachytene spermatocytes, condensing spermatids, and Sertoli cells. Immunoprecipitation-Western analysis detected both CKI proteins in isolated pachytene spermatocytes and round spermatids. CDK4/6-CKI complexes were detected in germ cells by co-immunoprecipitation, although the composition differed by cell type. p19(Ink4d) was also identified in FSH+ gonadotrophs, suggesting that this CKI may be independently required in the pituitary. Possible cell autonomous and paracrine mechanisms for the spermatogenic defects in mice lacking p18(Ink4c) or p19(Ink4d) are supported by expression of these CKIs in spermatogenic cells and in somatic cells of the testis and pituitary.

Anti-p19 antibody treatment exacerbates lyme arthritis and enhances borreliacidal activity

Considerable effort has been made to elucidate the mechanism of Lyme arthritis. We focused on p19, a cell cycle-regulating molecule, because it is known to inhibit cell cycle division of T lymphocytes which may be responsible for the induction of arthritis. We show that anti-p19 antibody treatment enhances the inflammatory response normally detected at the tibiotarsal joints of Borrelia burgdorferi-vaccinated and Borrelia bissettii-challenged mice. Specifically, anti-p19 antibody treatment augmented the severity of inflammation within the synovial and subsynovial tissue. Moreover, treatment with anti-p19 antibody caused severe erosion of cartilage and bone with ankle joint destruction. In addition, anti-p19 antibody treatment of Borrelia-vaccinated and -challenged mice enhanced the borreliacidal antibody response, especially against the vaccine isolate. The novel activities of anti-p19 antibody show that p19 may be an important therapeutic site for the treatment of Lyme arthritis.

Cell cycle inhibitor, p19INK4d, promotes cell survival and decreases chromosomal aberrations after genotoxic insult due to enhanced DNA repair

Genome integrity and cell proliferation and survival are regulated by an intricate network of pathways that includes cell cycle checkpoints, DNA repair and recombination, and programmed cell death. It makes sense that there should be a coordinated regulation of these different processes, but the components of such mechanisms remain unknown. In this report, we demonstrate that p19INK4d expression enhances cell survival under genotoxic conditions. By using p19INK4d-overexpressing clones, we demonstrated that p19INK4d expression correlates with the cellular resistance to UV treatment with increased DNA repair activity against UV-induced lesions. On the contrary, cells transfected with p19INK4d antisense cDNA show reduced ability to repair DNA damage and increased sensitivity to genotoxic insult when compared with their p19INK4d-overexpressing counterparts. Consistent with these findings, our studies also show that p19INK4d-overexpressing cells present not only a minor accumulation of UV-induced chromosomal aberrations but a lower frequency of spontaneous chromosome abnormalities than p19INK4d-antisense cells. Lastly, we suggest that p19INK4d effects are dissociated from its role as CDK4/6 inhibitor. The results presented herein support a crucial role for p19INK4d in regulating genomic stability and overall cell viability under conditions of genotoxic stress. We propose that p19INK4d would belong to a protein network that would integrate DNA repair, apoptotic and checkpoint mechanisms in order to maintain the genomic integrity.

Cell cycle regulated D3-type cyclins form active complexes with plant-specific B-type cyclin-dependent kinase in vitro

Tobacco (Nicotiana tabacum L.) cv Bright Yellow-2 (BY-2) cells are the most highly synchronizable plant cell culture, and previously we used them to analyze cell cycle regulation of cyclin-dependent kinases (CDKs) containing the cyclin binding motifs PSTAIRE (CDKA) and PPTA/TLRE (CDKB). Here we describe the analysis of tobacco CycD3 cyclins whose transcripts predominantly accumulate during G2 to M phase, which represents a unique feature of this type of cyclin D in plants. Although protein levels of CycD3s fluctuate with different patterns during the cell cycle, kinase assays revealed that the CycD3-associated kinases phosphorylate histone H1 and the tobacco retinoblastoma related protein (NtRBR1) with two peaks at the G1/S and G2/M boundaries. In vitro pull-down assays revealed that cell cycle-regulated CycD3s bind to CDKA, but more weakly than does CycD3;3, and that they also bind to CDKB and the CDK inhibitor NtKIS1a. Mutations in the cyclin box of the CycD3s showed that two amino acids are required for binding with CDKA and NtKIS1a, but no diminished interaction was observed with CDKB. A reconstituted kinase assay was adapted for use with bacterially produced GST-CycD3s, and kinase activity could be activated by incubation of extracts from exponentially growing BY-2 cells. Such activated complexes contained CDKA and CDKB, and the reconstituted GST-CycD3 mutants, retaining binding ability to CDKB, showed kinase activity, suggesting that these cell cycle-regulated CycD3s form active complexes with both A- and B-type CDKs in vitro.

Molecular biology of malignant mesothelioma: a review

Malignant mesothelioma (MM) is an uncommon tumor with high mortality and morbidity rates. It arises from mesothelial cells that line the pleural, pericardial, peritoneal, and testicular cavities. This is a disease with an indolent course because tumors arise 20 to 40 years after exposure to an inciting agent. Extensive research has shown that mesothelial cells are transformed into MM cells through various chromosomal and cellular pathway defects. These changes alter the normal cells' ability to survive, proliferate, and metastasize. This article discusses the alterations that occur in transforming normal mesothelial cells into MM. It also details some of the signal transduction pathways that seem to be important in MM with the potential for novel targeted therapeutics.

Molecular genetics of supratentorial primitive neuroectodermal tumors and pineoblastoma

The supratentorial primitive neuroectodermal tumors (PNETs) are a group of highly malignant lesions primarily affecting young children. Although these tumors are histologically indistinguishable from infratentorial medulloblastoma, they often respond poorly to medulloblastoma-specific therapy. Indeed, existing molecular genetic studies indicate that supratentorial PNETs have transcriptional and cytogenetic profiles that are different from those of medullo-blastomas, thus pointing to unique biological derivation for the supratentorial PNET. Due to the rarity of these tumors and disagreement about their histopathological diagnoses, very little is known about the molecular characteristics of the supratentorial PNET. Clearly, future concerted efforts to characterize the molecular features of these rare tumors will be necessary for development of more effective supratentorial PNET treatment protocols and appropriate disease models. In this article the authors review existing molecular genetic data derived from human and mouse studies, with the aim of providing some insight into the putative histogenesis of these rare tumors and the underlying transforming pathways that drive their development. Studies of the related but distinct pineoblastoma PNET are also reviewed.

Induction of p19INK4d in response to ultraviolet light improves DNA repair and confers resistance to apoptosis in neuroblastoma cells

The genetic instability driving tumorigenesis is fueled by DNA damage and by errors made by the DNA replication. Upon DNA damage the cell organizes an integrated response not only by the classical DNA repair mechanisms but also involving mechanisms of replication, transcription, chromatin structure dynamics, cell cycle progression, and apoptosis. In the present study, we investigated the role of p19INK4d in the response driven by neuroblastoma cells against DNA injury caused by UV irradiation. We show that p19INK4d is the only INK4 protein whose expression is induced by UV light in neuroblastoma cells. Furthermore, p19INK4d translocation from cytoplasm to nucleus is observed after UV irradiation. Ectopic expression of p19INK4d clearly reduces the UV-induced apoptosis as well as enhances the cellular ability to repair the damaged DNA. It is clearly shown that DNA repair is the main target of p19INK4d effect and that diminished apoptosis is a downstream event. Importantly, experiments performed with CDK4 mutants suggest that these p19INK4d effects would be independent of its role as a cell cycle checkpoint gene. The results presented herein uncover a new role of p19INK4d as regulator of DNA-damage-induced apoptosis and suggest that it protects cells from undergoing apoptosis by allowing a more efficient DNA repair. We propose that, in addition to its role as cell cycle inhibitor, p19INK4d is involved in maintenance of DNA integrity and, therefore, would contribute to cancer prevention.

S-phase entry of oligodendrocyte lineage cells is associated with increased levels of p21Cip1

The mechanisms regulating the number of myelinating cells in the central nervous system are crucial for both normal development and repair in pathological conditions. Among relevant growth factors involved in this process, fibroblast growth factor-2 (FGF2) induces oligodendrocyte progenitors (OLPs) to proliferate and stimulates mature oligodendrocytes (OLs) to reenter the S-phase of the cell cycle. S-phase entry is modulated by the formation of complexes between cyclins and cyclin-dependent kinases (CDKs), on one hand, and by their interactions with cell cycle inhibitors (e.g., p18INK, p27Kip1, p21Cip1), on the other. Although the roles of cyclin E/CDK2 complexes and the inhibitor p27Kip1 have been extensively investigated relative to proliferation and differentiation in the OL lineage, less is known about the regulation of the formation of cyclin D1/CDK4 complexes and the role of p21Cip1 in these events. In this study, we show that the FGF2-mediated increase in bromodeoxyuridine (BrdU) incorporation into OL progenitors and mature OLs occurs concomitantly with increase in the levels of p21Cip1 and the formation of p21Cip1/cyclin D1/CDK4 ternary complexes. These complexes are functionally active is indicated by the ensuing FGF2-dependent hyperphosphorylation of the downstream target Rb. In untreated mature OLs that do not incorporate BrdU, the levels of p21Cip1 are low, and the level of the inhibitor p18INK is high. Furthermore, p18INK sequesters CDK2 into binary complexes, precluding the formation of p21Cip1/cyclin D1/CDK4 ternary complexes in these cells. Therefore, we propose that p21Cip1 is acting as a positive regulator, rather than an inhibitor, of cell cycle entry by favoring the assembly of active cyclin D1/CDK4 complexes.

Genetic and biochemical interactions among Yar1, Ltv1 and Rps3 define novel links between environmental stress and ribosome biogenesis in Saccharomyces cerevisiae

In the yeast S. cerevisiae, ribosome assembly is linked to environmental conditions by the coordinate transcriptional regulation of genes required for ribosome biogenesis. In this study we show that two nonessential stress-responsive genes, YAR1 and LTV1, function in 40S subunit production. We provide genetic and biochemical evidence that Yar1, a small ankyrin-repeat protein, physically interacts with RpS3, a component of the 40S subunit, and with Ltv1, a protein recently identified as a substoichiometric component of a 43S preribosomal particle. We demonstrate that cells lacking YAR1 or LTV1 are hypersensitive to particular protein synthesis inhibitors and exhibit aberrant polysome profiles, with a reduced absolute number of 40S subunits and an excess of free 60S subunits. Surprisingly, both mutants are also hypersensitive to a variety of environmental stress conditions. Overexpression of RPS3 suppresses both the stress sensitivity and the ribosome biogenesis defect of Deltayar1 mutants, but does not suppress either defect in Deltaltv1 mutants. We propose that YAR1 and LTV1 play distinct, nonessential roles in 40S subunit production. The stress-sensitive phenotypes of strains lacking these genes reveal a hitherto unknown link between ribosome biogenesis factors and environmental stress sensitivity.

Cell cycle in mouse development

Mice likely represent the most-studied mammalian organism, except for humans. Genetic engineering in embryonic stem cells has allowed derivation of mouse strains lacking particular cell cycle proteins. Analyses of these mutant mice, and cells derived from them, facilitated the studies of the functions of cell cycle apparatus at the organismal and cellular levels. In this review, we give some background about the cell cycle progression during mouse development. We next discuss some insights about in vivo functions of the cell cycle proteins, gleaned from mouse knockout experiments. Our text is meant to provide examples of the recent experiments, rather than to supply an extensive and complete list.

Opposing roles for the cyclin-dependent kinase inhibitor p27kip1 in the control of CD4+ T cell proliferation and effector function

Cell division drives T cell clonal expansion and differentiation, and is the result of concerted signaling from Ag, costimulatory, and growth factor receptors. How these mitogenic signals are coupled to the cell cycle machinery in primary T cells is not clear. We have focused on the role of p27kip1, a major cyclin-dependent kinase binding protein expressed by CD4+ T cells. Our studies using p27kip1 gene dosage demonstrate that early after activation, p27kip1 acts to promote, rather than inhibit, G1 to S phase progression within the first division cycle. However, throughout subsequent cell divisions p27kip1 behaves as a negative regulator, directly establishing the threshold amount of growth factor signaling required to support continued cell division. During this phase, signals from CD28 and IL-2R cooperate with the TCR to "tune" this threshold by inducing the degradation of p27kip1 protein, and we show that agents that block these pathways require elevated p27kip1 levels for their full antiproliferative activity. Finally, we show that p27kip1 opposes the development of CD4+ T cell effector function, and is required for the full development of anergy in response to a tolerizing stimulus. Our results suggest that p27kip1 plays a complex and important role in the regulation of cell division and effector function in primary CD4+ T cells.

Biochemical and cellular mechanisms of mammalian CDK inhibitors: a few unresolved issues

p21 and p16, first identified as two small molecular weight proteins in CDK and cyclin immunocomplexes, represent two distinct families constituting a total of seven CDK inhibitors in mammalian cells. The physiological functions of these genes are believed to be broadly involved in connecting various cellular pathways to cell cycle control. Extensive studies over the past 10 years have led to a fairly clear understanding of their biochemical and cellular mechanisms and have also left some unresolved and controversial issues.

Trichostatin A activates p18INK4c gene: differential activation and cooperation with p19INK4d gene

We have reported that histone deacetylase (HDAC) inhibitors activate a member of the INK4 family, the p19INK4d gene, causing G1 phase arrest. We report here that HDAC inhibitor, Trichostatin A, activates another member of the INK4 family, the p18INK4c gene, through its promoter in Jurkat cells. Interestingly, the activation patterns of the p18INK4c gene were different from those of p19INK4d. Furthermore, mouse embryo fibroblasts lacking p18Ink4c or p18Ink4c/p19Ink4d were resistant to the growth inhibitory effects of TSA as compared to their wild-type counterpart. Our findings suggest that p18INK4c is involved in TSA-mediated cell growth inhibition and cooperates with p19INK4d.

Protein kinase CK2 is an inhibitor of the neuronal Cdk5 kinase

The complex of Cdk5 and its neuronal activator p35 is a proline-directed Ser/Thr kinase that plays an important role in various neuronal functions. Deregulation of the Cdk5 enzymatic activity was found to associate with a number of neurodegenerative diseases. To search for regulatory factors of Cdk5-p35 in the brain, we developed biochemical affinity isolation using a recombinant protein comprising the N-terminal 149 amino acids of p35. The catalytic alpha-subunit of protein kinase CK2 (formerly known as casein kinase 2) was identified by mass spectrometry from the isolation. The association of CK2 with p35 and Cdk5 was demonstrated, and the CK2-binding sites were delineated in p35. Furthermore, CK2 displayed strong inhibition toward the Cdk5 activation by p35. The Cdk5 inhibition is dissociated from the kinase function of CK2 because the kinase-dead mutant of CK2 displayed the similar Cdk5 inhibitory activity as the wild-type enzyme. Further characterization showed that CK2 blocks the complex formation of Cdk5 and p35. Together, these findings suggest that CK2 acts as an inhibitor of Cdk5 in the brain.

Gene expression profiling and identification of novel prognostic marker genes in neuroblastoma

To investigate the various genetic characteristics of and differences between early- and advanced-stage neuroblastoma (NB) and to identify candidate genes involved in NB progression, we performed DNA microarray analysis on 20 primary tumors. Two-way clustering analysis based on the expression pattern of approximately 500 of 1,700 genes revealed genetic subgroups in these NB tumors. Although 9 of the 13 early-stage tumors (69%) and 4 of the 6 advanced-stage tumors (67%) were classified as being in the same cluster, the remaining tumors showed different expression profiles. This indicates that both the early- and advanced-stage tumors were heterogeneous. Based on the microarray data, we identified the BIRC, CDKN2D, and SMARCD3 genes as those that are predominantly expressed in either the early or the advanced stage of NB. These genes have been reported to be associated with apoptosis, cell cycles, and the transcriptional activator, respectively. To better assess the prognostic value of the expression of these genes in NB, real-time polymerase chain reaction was carried out on 50 primary tumors. The expression of both the BIRC3 and CDKN2D genes was significantly higher in the early-stage group than in the advanced-stage group (P = 0.002 and 0.003, respectively), whereas the expression of the SMARCD3 gene was significantly reduced in the early-stage group (P = 0.02). Therefore, the BIRC, CDKN2D, and SMARCD3 genes are possible candidates for being novel prognostic markers for NB.

BRD7, a novel bromodomain gene, inhibits G1-S progression by transcriptionally regulating some important molecules involved in ras/MEK/ERK and Rb/E2F pathways

Bromodomain is a 110 amino acid domain. It is evolutionally conserved and is found in proteins strongly implicated in signal-dependent transcriptional regulation. BRD7 is a novel bromodomain gene and it is downexpressed in nasopharyngeal carcinoma (NPC) biopsies and cell lines; its function is poorly understood. In the present study, tet-on inducible expression system was used to investigate the role of BRD7 in cell growth and cell cycle progression. We found that ectopic expression of BRD7 in NPC cells inhibited cell growth and cell cycle progression from G1 to S. We further performed cell cycle cDNA array to screen potential transcriptional targets of BRD7 in cell cycle. Thirteen important signaling molecules, mainly implicated in ras/MEK/ERK and Rb/E2F pathways, were differentially expressed by induction of BRD7. Moreover, we observed that BRD7 could regulate the promoter activity of E2F3, one of its targets. Taken together, the present study indicated that BRD7 inhibited G1-S progression by transcriptionally regulating some important molecules involved in ras/MEK/ERK and Rb/E2F pathways and suggested that BRD7 may present a promising candidate of NPC trade mark associated tumor suppressor gene.

Histone deacetylase inhibitors activate INK4d gene through Sp1 site in its promoter

Histone deacetylase (HDAC) inhibitors are known to arrest human tumor cells at the G1 phase of the cell cycle and activate the cyclin-dependent kinase inhibitor, p21(WAF1/Cip1). However, several studies have suggested the existence of a p21(WAF1/Cip1)-independent molecular pathway. We report here that HDAC inhibitors activate a member of the INK4 family, the INK4d gene, causing G1 phase arrest, in the human T cell leukemia cell line, Jurkat. One of the major Trichostatin A (TSA)-responsive elements is a specific Sp1 binding site in the INK4d promoter. Electrophoretic mobility-shift assay revealed that Sp1 and Sp3 can specifically interact with this Sp1 binding site. Furthermore, using chromatin immunoprecipitation assay, we demonstrated that HDAC2 was present in the INK4d proximal promoter region in the absence, but not the presence, of TSA. Taken together, these results suggest that treatment with TSA transcriptionally activates INK4d by releasing HDAC2 from the histone-DNA complex at the INK4d promoter. Using a p21(WAF1/Cip1)-deleted human colorectal carcinoma cell line, HCT116 p21 (-/-), we show that upregulation of p19(INK4d) by TSA is associated with inhibition of cell proliferation. Moreover, mouse embryo fibroblasts lacking Ink4d were resistant to the growth inhibitory effects of TSA as compared to their wild-type counterpart. Our findings suggest that p19(INK4d) in addition to p21(WAF1/Cip1) is an important molecular target of HDAC inhibitors inducing growth arrest.

Cell-cycle control of plasma cell differentiation and tumorigenesis

Cell-cycle control is a major determinant of homeostasis during B-cell development, differentiation, and tumorigenesis. The generation of an antibody response requires activation and expansion of antigen-specific B cells and terminal differentiation of these cells into plasma cells. Plasma cells arrest in the G1 phase of the cell cycle, but the mechanism that underlies timely cell-cycle entry and exit in the humoral immune response is not known. The mammalian cell-cycle is regulated primarily at the G1 to S transition by the balance between positive regulators, the cyclin-dependent kinases (CDK) together with cyclins, and negative regulators, the CDK inhibitors. One such inhibitor, p18INK4c, has been shown to be required for cell-cycle termination and final differentiation of non-secreting plasmacytoid cells to antibody-secreting plasma cells. This finding provides the first direct evidence for cell-cycle control of B-cell immunity. It also raises important questions regarding cell-cycle control of cellular differentiation, apoptosis, and earlier steps of B-cell terminal differentiation. This article discusses the biochemical mechanism of cell-cycle control in the context of antibody response and plasma cell differentiation along with the role of cell-cycle dysregulation in the pathogenesis of multiple myeloma, the plasma cell cancer.

Epigenetic and genetic analysis of p16 in dermal fibroblasts from type 1 diabetic patients with nephropathy

BACKGROUND

Several studies have shown that cultured skin fibroblasts from patients with diabetic nephropathy (DN) exhibit a hyperplastic growth phenotype. Increased DNA synthesis in cells from patients with DN may ultimately involve alterations in cell cycle regulatory proteins. p16 protein is a member of INK4 family of cyclin-dependent kinase inhibitors, which plays an important role in cell cycle regulation. In this study, we examined the correlation between p16 protein expression in cultured dermal fibroblasts from type 1 diabetic patients and the presence of DN.

METHOD

Western blot analysis was performed to compare p16 protein expression in skin fibroblasts from patients with DN as compared to control subjects, diabetic patients without DN, and nondiabetic patients with nephropathy. Transcriptional regulation of the p16 gene was assessed using competitive reverse transcription-polymerase chain reaction (RT-PCR). Methylation status of the promoter region of p16 was examined using methylation-specific PCR, and we used single-stranded conformational polymorphism (SSCP)-PCR to assess p16 single-nucleotide polymorphism.

RESULTS

Cells from diabetic patients with DN had nondetectable to significantly lower protein expression of p16. Similarly, mRNA expression of p16 was significantly lower in diabetic patients with DN. No hypermethylation of p16 gene was detected, and no abnormal migrating bands were noticed on SSCP-PCR analysis in cells from patients with DN.

CONCLUSION

Our data indicate that cells from patients with DN exhibit significantly lower protein and mRNA expression of p16. This study could have not only important implications for the understanding of the pathogenesis of DN, but also the absence of p16 may ultimately serve as an early marker for DN.

Microarray analysis of lipopolysaccharide-treated human neutrophils

Neutrophils respond to infection by degranulation, release of reactive oxygen intermediates, and secretion of chemokines and cytokines; however, activation of neutrophil transcriptional machinery has been little appreciated. Recent findings suggest that gene expression may represent an additional neutrophil function after exposure to lipopolysaccharide (LPS). We performed microarray gene expression analysis of 4,608 mostly nonredundant genes on LPS-stimulated human neutrophils. Analysis of three donors indicated some variability but also a high degree of reproducibility in gene expression. Twenty-eight verifiable, distinct genes were induced by 4 h of LPS treatment, and 13 genes were repressed. Genes other than cytokines and chemokines are regulated; interestingly, genes involved in cell growth regulation and survival, transcriptional regulation, and interferon response are among those induced, whereas genes involved in cytoskeletal regulation are predominantly repressed. In addition, we identified monocyte chemoattractant protein-1 as a novel LPS-regulated chemokine in neutrophils. Included in these lists are five clones with no defined function. These data suggest molecular mechanisms by which neutrophils respond to infection and indicate that the transcriptional potential of neutrophils is greater than previously thought.

Evidence of a role for the INK4 family of cyclin-dependent kinase inhibitors in ovarian granulosa cell tumors

Granulosa cell tumors (GCTs) of the ovary are relatively rare and account for <5% of all ovarian cancers. The molecular pathogenesis of these tumors is not well understood. We tested the hypothesis that cyclin-dependent kinase inhibitors, specifically the inhibitors of the cyclin-dependent kinase 4 (INK4) family, are targets for altered gene expression in GCTs. The status of RB1, INK4A, INK4B, INK4C, INK4D, and ARF in 13 adult and 2 juvenile ovarian GCTs was determined by reverse transcription-polymerase chain reaction of total RNA and exon-specific sequencing of genomic DNA. Tumors showing loss of INK4A expression were assayed further by exon-deletion analysis and methylation-specific PCR. None of the juvenile tumors demonstrated altered expression, but 7/12 (58%) adult GCTs lacked expression of INK4A, INK4B, or both. In one of these cases, we noted a homozygous deletion of the INK4A locus, and in the remaining tumors we found hypermethylation of the promoter region, a mechanism that can lead to gene inactivation. These data support a role for the INK4 family of CDK inhibitors in the biology of GCTs.

CDK inhibitor p18(INK4c) is required for the generation of functional plasma cells

B cell terminal differentiation is associated with the onset of high-level antibody secretion and cell cycle arrest. Here the cyclin-dependent kinase (CDK) inhibitor p18(INK4c) is shown to be required within B cells for both terminating cell proliferation and differentiation of functional plasma cells. In its absence, B cells hyperproliferate in germinal centers and extrafollicular foci in response to T-dependent antigens but serum antibody titers are severely reduced, despite unimpaired germinal center formation, class switch recombination, variable region-directed hypermutation, and differentiation to antibody-containing plasmacytoid cells. The novel link between cell cycle control and plasma cell differentiation may, at least in part, relate to p18(INK4c) inhibition of CDK6. Cell cycle arrest mediated by p18(INK4C) is therefore requisite for the generation of functional plasma cells.

4-Hydroxynonenal affects pRb/E2F pathway in HL-60 human leukemic cells

4-Hydroxynonenal (HNE), a highly reactive product of lipid peroxidation, has an antiproliferative effect in several tumor cell lines and provokes alteration of cell cycle progression in HL-60 cells. HNE down-regulates c-myc expression in K562, HL-60, and MEL cells. This prompted us to study the cascade of phenomena that, starting from the CKIs expression and the phosphorylation of pRb, arrives at the E2F binding to consensus sequence in the P2 promoter of the c-myc gene. Treatment of HL-60 cells with HNE (1 microM) causes a p53-independent increase of p21(WAF1/CIP1) expression, pRb dephosphorylation, a decrease of low molecular weight E2F complexes and an increase of high molecular weight E2F complexes bound to P2 c-myc promoter. E2F4 expression is reduced by HNE treatment as well as the amount of pRb/E2F4 complexes, whereas the amount of pRb/E2F1 complexes is increased. In conclusion, HNE can affect the pRb/E2F pathway by modifying the expression of several genes involved in the control of cell proliferation.

Increased expression of unmethylated CDKN2D by 5-aza-2'-deoxycytidine in human lung cancer cells

DNA hypermethylation of CpG islands in the promoter region of genes is associated with transcriptional silencing. Treatment with hypo-methylating agents can lead to expression of these silenced genes. However, whether inhibition of DNA methylation influences the expression of unmethylated genes has not been extensively studied. We analysed the methylation status of CDKN2A and CDKN2D in human lung cancer cell lines and demonstrated that the CDKN2A CpG island is methylated, whereas CDKN2D is unmethylated. Treatment of cells with 5-aza-2'-deoxycytidine (5-Aza-CdR), an inhibitor of DNA methyltransferase 1, induced a dose and duration dependent increased expression of both p16(INK4a) and p19(INK4d), the products of CDKN2A and CDKN2D, respectively. These data indicate that global DNA demethylation not only influences the expression of methylated genes but also of unmethylated genes. Histone acetylation is linked to methylation induced transcriptional silencing. Depsipeptide, an inhibitor of histone deacetylase, acts synergistically with 5-Aza-CdR in inducing expression of p16(INK4a) and p19(INK4d). However, when cells were treated with higher concentrations of 5-Aza-CdR and depsipeptide, p16(INK4a) expression was decreased together with significant suppression of cell growth. Interestingly, p19(INK4d) expression was enhanced even more by the higher concentrations of 5-Aza-CdR and depsipeptide. Our data suggest that p19(INK4d) plays a distinct role from other INK4 family members in response to the cytotoxicity induced by inhibition of DNA methylation and histone deacetylation.

One INK4 gene and no ARF at the Fugu equivalent of the human INK4A/ARF/INK4B tumour suppressor locus

The INK4A/ARF/INK4B locus, conserved in mammals, encodes three polypeptides that regulate cell proliferation via the pRb and p53 tumour suppressor pathways. The locus is mutated in many cancers. The related, tandemly-linked INK4A and INK4B genes encode the p16(INK4A) and p15(INK4B) members of the INK4 family of cyclin-dependent kinase inhibitors which block phosphorylation of pRb, whereas the third product, ARF, derived from an alternative reading frame of INK4A, regulates p53 activity. We assessed the status of this unusual locus in the puffer fish, Fugu rubripes, and identified two INK4 genes using degenerate PCR and hybridization analyses. Sequence conservation and conservation of synteny between human and Fugu predict one gene to be an INK4A or INK4B homologue and the other an INK4D homologue. Analysis of the Fugu INK4A/B gene and the surrounding 40-kb of genomic DNA did not reveal the presence of any ARF-encoding potential or another related INK4 gene. We conclude that the gene duplication event that generated adjacent INK4A and INK4B genes and the association of ARF with the ancestral INK4A gene occurred after the divergence of the lineage leading to mammals from fish. Thus, unlike mammals, the fish p53 and pRb tumour suppressor pathways are not regulated by a single locus.

An important role of CDK inhibitor p18(INK4c) in modulating antigen receptor-mediated T cell proliferation

The inhibitors of cyclin-dependent kinase (CDK) 4 (INK4) bind CDK4/6 to prevent their association with D-cyclins and G(1) cell cycle initiation and progression. We report here that among the seven CDK inhibitors, p18(INK4c) played an important role in modulating TCR-mediated T cell proliferation. Loss of p18(INK4c) in T cells led to hyperproliferation in response to CD3 stimulation. p18(INK4c)-null mice developed lymphoproliferative disorder and T cell lymphomas. Expression of IL-2, IL-2R-alpha, and the major G(1) cell cycle regulatory proteins was not altered in p18-null T cells. Both FK506 and rapamycin efficiently inhibited proliferation of p18-null T cells. In activated T cells, p18(INK4c) remained constant, and preferentially associated with and inhibited CDK6 but not CDK4. We propose that p18(INK4c) sets an inhibitory threshold in T cells and one function of CD28 costimulation is to counteract the p18(INK4c) inhibitory activity on CDK6-cyclin D complexes. The p18(INK4c) protein may provide a novel target to modulate T cell immunity.

p27-p16 fusion gene inhibits angioplasty-induced neointimal hyperplasia and coronary artery occlusion

Inhibition of proliferative neointima formed by vascular smooth muscle cells is a potential target in preventing angioplasty-induced restenosis. We have created a potent antiproliferative by fusing the active regions of the p27 and p16 cell cycle inhibitors. Intravascular delivery of a replication-deficient adenoviral vector (AV) encoding this p27-p16 fusion protein, named W9, inhibited balloon injury-induced neointimal hyperplasia in rabbit carotid arteries. In a therapeutically more relevant model, AV-W9 was delivered to balloon-injured porcine coronary arteries in vivo using an infusion catheter. Of the three coronary arteries, two were injured with a 15-mm balloon catheter and either were left untreated or were treated with 10(12) viral particles of either AV-W9 or a control null virus. AV-W9 treatment significantly inhibited neointimal hyperplasia in this porcine arterial balloon injury model compared with untreated or control virus-treated vessels. The average intimal area of the AV-W9-treated group 10 days after balloon injury and treatment was 0.42+/-0.36 mm(2), whereas the AV-null group demonstrated an intimal area of 0.70+/-0.52 mm(2). At day 10 the average intimal thickness of the AV-W9-treated vessels was 9.1 microm (n=5, x 20 magnification) compared with 21.2 microm (n=5, x 20 magnification) in control virus-treated vessels. This trend was also observed at 28 days after balloon injury and gene transfer during which AV-W9-treated vessels demonstrated an average intimal thickness of 4.7 microm (n=8, x 20 magnification) compared with 13.3 microm (n=3, x 20 magnification) in control virus-treated vessels and 7.3 microm (n=5, x 20 magnification) in the sham-treated vessels. The AV-W9 treatment was safe and well tolerated. These data suggest that AV-W9 gene therapy may be useful in preventing angioplasty-induced intimal hyperplasia in the coronary artery.

Inhibitory effects of 1alpha,25-dihydroxyvitamin D(3) on the G(1)-S phase-controlling machinery

The nuclear hormone 1alpha,25-dihydroxyvitamin D(3) induces cell cycle arrest, differentiation, or apoptosis depending on target cell type and state. Although the antiproliferative effect of 1alpha,25-dihydroxyvitamin D(3) has been known for years, the molecular basis of the cell cycle blockade by 1alpha,25-dihydroxyvitamin D(3) remains largely unknown. Here we have investigated the mechanisms underlying the G(1) arrest induced upon 1alpha,25-dihydroxyvitamin D(3) treatment of the human breast cancer cell line MCF-7. Twenty-four-hour exposure of exponentially growing MCF-7 cells to 1alpha,25-dihydroxyvitamin D(3) impeded proliferation by preventing S phase entry, an effect that correlated with appearance of the growth-suppressing, hypophosphorylated form of the retinoblastoma protein (pRb), and modulation of cyclin-dependent kinase (cdk) activities of cdk-4, -6, and -2. Time course immunochemical and biochemical analyses of the cellular and molecular effects of 1alpha,25-dihydroxyvitamin D(3) treatment for up to 6 d revealed a dynamic chain of events, preventing activation of cyclin D1/cdk4, and loss of cyclin D3, which collectively lead to repression of the E2F transcription factors and thus negatively affected cyclin A protein expression. While the observed 10-fold inhibition of cyclin D1/cdk 4-associated kinase activity appeared independent of cdk inhibitors, the activity of cdk 2 decreased about 20-fold, reflecting joint effects of the lower abundance of its cyclin partners and a significant increase of the cdk inhibitor p21(CIP1/WAF1), which blocked the remaining cyclin A(E)/cdk 2 complexes. Together with a rapid down-modulation of the c-Myc oncoprotein in response to 1alpha,25-dihydroxyvitamin D(3), these results demonstrate that 1alpha,25-dihydroxyvitamin D(3) inhibits cell proliferation by targeting several key regulators governing the G(1)/S transition.

Gene expression profile in response to chromium-induced cell stress in A549 cells

Chromium (Cr) is a trace element required for life. Biological activities of Cr are complicated and remain to be fully investigated. It is known that the valence of Cr plays an important role in the biological activities of Cr. For example, Cr (VI) is classified as a metal carcinogen, but Cr (III) is widely used as a nutritional supplement. Establishment of a gene expression profile for Cr-induced cellular response is necessary to facilitate investigation of the biological activities of Cr. In the present study, a large-scale gene expression analysis was conducted using RNA of human lung epithelial cells after in vitro exposure to Cr (VI). Utilizing high-density oligonucleotide arrays representing 2400 genes, we observed that expression of 150 genes was up-regulated, and that of 70 genes were down-regulated by Cr (VI). Functional analysis of these responsive genes led to an outline of potential biological activities of Cr in six aspects. The gene expression profile reveals that Cr may involves in redox stress, calcium mobilization, energy metabolism, protein synthesis, cell cycle regulation and carcinogenesis in the cell. The results provide a critical clue for understanding molecular mechanisms of the biological activities of Cr.

Disturbance of neuronal plasticity is a critical pathogenetic event in Alzheimer's disease

Brain areas affected by AD pathology are primarily those structures that are invovled in the regulation of "higher brain functions". The functions these areas subserve such as learning, memory, perception, self-awareness, and consciousness require a life-long re-fittng of synaptic contacts that allows for the acquistion of new epigenetic information, a process based on a particularly high degree of structural plasticity. Here, we outline a hypothesis that it is the "labile state fo differentiation" of a subset of neurons in the adult brain that allows for ongoing neuroplastic processes after development is completed but at the same time renders these neurons particularly vulnerable. Mechanisms of molecular and cellular control of neuronal differentiation and proliferation might, thus, not only play a role during development but critically involved in the pathogenesis of neurodegeneration.

Alzheimer's disease as a disorder of mechanisms underlying structural brain self-organization

Mental function has as its cerebral basis a specific dynamic structure. In particular, cortical and limbic areas involved in "higher brain functions" such as learning, memory, perception, self-awareness and consciousness continuously need to be self-adjusted even after development is completed. By this lifelong self-optimization process, the cognitive, behavioural and emotional reactivity of an individual is stepwise remodelled to meet the environmental demands. While the presence of rigid synaptic connections ensures the stability of the principal characteristics of function, the variable configuration of the flexible synaptic connections determines the unique, non-repeatable character of an experienced mental act. With the increasing need during evolution to organize brain structures of increasing complexity, this process of selective dynamic stabilization and destabilization of synaptic connections becomes more and more important. These mechanisms of structural stabilization and labilization underlying a lifelong synaptic remodelling according to experience, are accompanied, however, by increasing inherent possibilities of failure and may, thus, not only allow for the evolutionary acquisition of "higher brain function" but at the same time provide the basis for a variety of neuropsychiatric disorders. It is the objective of the present paper to outline the hypothesis that it might be the disturbance of structural brain self-organization which, based on both genetic and epigenetic information, constantly "creates" and "re-creates" the brain throughout life, that is the defect that underlies Alzheimer's disease (AD). This hypothesis is, in particular, based on the following lines of evidence. (1) AD is a synaptic disorder. (2) AD is associated with aberrant sprouting at both the presynaptic (axonal) and postsynaptic (dendritic) site. (3) The spatial and temporal distribution of AD pathology follows the pattern of structural neuroplasticity in adulthood, which is a developmental pattern. (4) AD pathology preferentially involves molecules critical for the regulation of modifications of synaptic connections, i.e. "morphoregulatory" molecules that are developmentally controlled, such as growth-inducing and growth-associated molecules, synaptic molecules, adhesion molecules, molecules involved in membrane turnover, cytoskeletal proteins, etc. (5) Life events that place an additional burden on the plastic capacity of the brain or that require a particularly high plastic capacity of the brain might trigger the onset of the disease or might stimulate a more rapid progression of the disease. In other words, they might increase the risk for AD in the sense that they determine when, not whether, one gets AD. (6) AD is associated with a reactivation of developmental programmes that are incompatible with a differentiated cellular background and, therefore, lead to neuronal death. From this hypothesis, it can be predicted that a therapeutic intervention into these pathogenetic mechanisms is a particular challenge as it potentially interferes with those mechanisms that at the same time provide the basis for "higher brain function".