A hantavirus causing hemorrhagic fever with renal syndrome requires gC1qR/p32 for efficient cell binding and infection

Hantaan virus (HTNV) is a pathogenic hantavirus that causes hemorrhagic fever with renal syndrome (HFRS). HTNV infection is mediated by αvβ3 integrin. We used protein blots of Vero E6 cell homogenates to demonstrate that radiolabeled HTNV virions bind to gC1qR/p32, the acidic 32-kDa protein known as the receptor for the globular head domain of complement C1q. RNAi-mediated suppression of gC1qR/p32 markedly reduced HTNV binding and infection in human lung epithelial A549 cells. Conversely, transient expression of either simian or human gC1qR/p32 rendered non-permissive CHO cells susceptible to HTNV infection. These results suggest an important role for gC1qR/p32 in HTNV infection and pathogenesis.     

Inverse expression of Jun activation domain binding protein 1 and cell cycle inhibitor p27Kip1: influence on proliferation in hepatocellular carcinoma

Recently, the functional role of Jun activation domain binding protein 1 (Jab1) as a putative novel oncogene in hepatocellular carcinoma (HCC) has been postulated. We show that expression of p27(Kip1), a negative cell cycle regulator, correlates inversely with Jab1 expression in HCC (P = .014). We observed nuclear Jab1 expression in 57% (55/97) and p27(Kip1) expression in 32% (31/97) of HCCs. Neither Jab1 nor p27(Kip1) nor inverse Jab1 and p27(Kip1) expression correlated with clinicopathological parameters. However, HCCs lacking p27(Kip1) with increased proliferative activity were frequently found to express Jab1 (P = .048). Normal liver tissue, cirrhosis, and tumor-like lesions (focal nodular hyperplasia, dysplastic nodules in cirrhotic liver) showed no significant Jab1 expression. In transfection studies in the hepatoma cell line Huh 7, Jab1 overexpression resulted in reduced p27(Kip1) protein levels. We conclude that Jab1 expression may lead to down-regulation of the negative cell cycle regulator p27(Kip1), pointing to a possible mechanism that promotes hepatocarcinogenesis.     

Expression of Pirh2, a p27(Kip1) ubiquitin ligase, in hepatocellular carcinoma: correlation with p27(Kip1) and cell proliferation

p53-Induced ring-H2 protein (Pirh2), a recently identified ubiquitin-protein ligase, interacts with p27(Kip1) to promote ubiquitination of p27(Kip1) independently of p53. High Pirh2 and low p27(Kip1) immunoreactivity are associated with a poor prognosis in several cancers, including resistant phenotypes. In the present study, we investigated the role of Pirh2 and p27(Kip1) in human hepatocellular carcinoma (HCC) progression. Immunohistochemical analysis was performed on formalin-fixed paraffin sections of 87 specimens. Statistical analysis showed that expression of Pirh2 was negatively related to p27(Kip1) expression (r = 0.787; P < .05), and Pirh2 expression correlated significantly with histologic grade (P < .001), venous invasion (P = .004), tumor size (P = .024), and the presence of multiple tumor-bearing lymph nodes (P = .017), whereas p27(Kip1) expression correlated significantly with histologic grade (P < .001), venous invasion (P = .048), and cirrhosis (P = .028). By Kaplan-Meier analysis, the survival curves of low versus high expressers of Pirh2 and p27(Kip1) showed significant separation (P < .01). Molecular interaction could be demonstrated between Pirh2 and p27(Kip1) in three HCC cell lines. In vitro, following release of two HCC cell lines from serum starvation, the expression of Pirh2 was upregulated, whereas p27(Kip1) was downregulated. Our results suggest that Pirh2 mediates the degradation of p27(Kip1) and participates in cell proliferation in human HCC. These findings provide a rational framework for further development of Pirh2 inhibitors as a novel class of anti-tumor agents.     

Identification of the gC1qR sites for the HIV-1 viral envelope protein gp41 and the HCV core protein: Implications in viral-specific pathogenesis and therapy

A substantial body of evidence accumulated over the past 20 years supports the concept that gC1qR is a major pathogen-associated pattern recognition receptor (PRR). This conclusion is based on the fact that, a wide range of bacterial and viral ligands are able to exploit gC1qR to either suppress the host’s immune response and thus enhance their survival, or to gain access into cells to initiate disease. Of the extensive array of viral ligands that have affinity for gC1qR, the HIV-1 envelope glycoprotein gp41, and the core protein of hepatitis C virus (HCV) are of major interest as they are known to contribute to the high morbidity and mortality caused by these pathogens. While the HCV core protein binds gC1qR and suppresses T cell proliferation resulting in a significantly diminished immune response, the gp41 employs gC1qR to induce the surface expression of the NK cell ligand, NKp44L, on uninfected CD4⁺ T cells, thereby rendering them susceptible to autologous destruction by NKp44 receptor expressing NK cells. Because of the potential for the design of peptide-based or antibody-based therapeutic options, the present studies were undertaken to define the gC1qR interaction sites for these pathogen-associated molecular ligands. Employing a solid phase microplate-binding assay, we examined the binding of each viral ligand to wild type gC1qR and 11 gC1qR deletion mutants. The results obtained from these studies have identified two major HCV core protein sites on a domain of gC1qR comprising of residues 144–148 and 196–202. Domain 196–202 in turn, is located in the last half of the larger gC1qR segment encoded by exons IV–VI (residues 159–282), which was proposed previously to contain the site for HCV core protein. The major gC1qR site for gp41 on the other hand, was found to be in a highly conserved region encoded by exon IV and comprises of residues 174–180. Interestingly, gC1qR residues 174–180 also constitute the cell surface-binding site for soluble gC1qR (sgC1qR), which can bind to the cell surface in an autocrine/paracrine manner via surface expressed fibrinogen or other membrane molecules. The identification of the sites for these viral ligands should therefore provide additional targets for the design of peptide-based or antigen-based therapeutic strategies.     

Reduced expression of the cell-cycle inhibitor p27Kip1 is associated with progression and lymph node metastasis of gastric carcinoma

AIMS: p27Kip1 (p27), a cyclin-dependent kinase inhibitor, plays an important role as inhibiting the progression of the cell cycle. Decreased expression of p27 is associated with high histological grade and aggressiveness of several human tumours. We aimed to evaluate the role of p27 in the progression and metastasis of gastric carcinoma. METHODS AND RESULTS: We analysed the expression of p27 in 67 primary gastric carcinomas and 31 lymph node metastases by immunohistochemistry. Reduced expression of p27 was found more frequently in advanced gastric cancer (40.9%) than in early gastric cancer (15.6%) (P < 0.001). Decreased p27 expression correlated with large tumour size, high histological grade, lymphatic invasion, advanced stage, deep invasion, lymph node metastasis and recurrence. The expression of p27 showed an inverse correlation with the Ki67 labelling index. There was a significant reduction of p27 expression in metastatic tumour cells in lymph nodes (mean positive cells: 3. 7%) when compared to the corresponding primary gastric carcinomas (mean positive cells: 8.1%) (P = 0.008). CONCLUSIONS: Alterations of p27 expression may play an important role in the progression and metastasis to lymph node of tumour cells in human gastric carcinoma.     

Hepatitis C virus core protein expression leads to biphasic regulation of the p21 cdk inhibitor and modulation of hepatocyte cell cycle

Hepatitis C virus (HCV) Core protein is implicated in viral pathogenesis by the modulation of hepatocyte gene expression and function. To determine the effect of Core protein on the cell-cycle control of hepatocytes, a HepG2 cell line containing a Flag-tagged Core under the control of an inducible promoter was generated. Initial Core protein expression included the presence of unprocessed (191 aa) and processed (173 aa) forms of the Core proteins with the processed form becoming dominant later. Expression of the 191 aa form of Core protein corresponded to an increase in the expression of the p21, a decrease in cdk2-dependent kinase activity, and a decrease in the percentage of cells in S-phase along with an accumulation of cells in the G(0)/G(1) phase of the cell cycle. As the processed form accumulated, the p21 levels started to decline, suggesting that Core protein regulates p21 expression in a biphasic manner. These findings implicate Core protein in potentially modulating hepatocyte cell cycle differentially in the early stages of infection through biphasic regulation of p21 cdk kinase inhibitor.     

Cyclin-dependent kinase inhibitor p27Kip1 controls growth and cell cycle progression in human uterine leiomyoma

The molecular mechanism of the cell-cycle machinery in uterine leiomyoma has not yet been fully elucidated. Among the various types of cell-cycle regulators, p27(Kip1) (p27) is considered to be a potent tumor suppressor. To provide further molecular basis for understanding the progression of uterine leiomyoma, our objective was to evaluate the expression level of p27 in normal myometrium and uterine leiomyoma tissue and its effect on cytogenic growth. Western blot analysis, real-time polymerase chain reaction (PCR) and immunohistochemical staining revealed that p27 protein and messenger RNA were down-regulated in uterine leiomyoma tissue and cultured cells compared to normal myometrium. Full-length human p27 cDNA was transferred using a replication-deficient recombinant adenoviral vector (Ad.p27) into uterine leiomyoma cells and evaluated the effect on cell proliferation. Transfection of Ad.p27 into uterine leiomyoma cells resulted in the induction of apoptosis, reduction in viability and proliferation of uterine leiomyoma cells. Our results suggest a new paradigm that down-regulated p27 protein expression is the possible underlying mechanism for the growth of uterine leiomyoma and over-expression of p27 induces cell death. This study provides better understanding of the control exerted by p27 in regulating growth and disease progression of uterine leiomyoma.     

The human papillomavirus type 16 E5 oncoprotein synergizes with EGF-receptor signaling to enhance cell cycle progression and the down-regulation of p27

E5 oncoprotein activity from high risk human papillomaviruses (HPVs) is associated with growth factor receptor signaling, but the function of this protein is not well understood. In this study, we investigated the role of HPV-16 E5 on the cell cycle progression during EGF-stimulation. Wild-type and NIH 3T3 cells over-expressing human EGF-receptor were transfected with HPV-16 E5 gene and the cell cycle progression was characterized. This analysis showed that the E5-expressing cells increased DNA synthesis (S-phase) by around 40%. Cell cycle protein analysis of E5-expressing cells showed a reduction in the half-life of p27^Kip1 protein as compared to control cells (18.4 vs. 12.7 h), an effect that was enhanced in EGF-stimulated cells (12.8 vs. 3.6 h). Blockage of EGF-receptor activity abrogated E5 signals as well as p27^Kip1 down-regulation. These results suggest that E5 and the EGF-receptor cooperate to enhance cell cycle entry and progression through regulating p27^Kip1 expression at protein level.     

Rho GTPases and cell cycle control

Members of the Rho family of small GTPases are crucial regulators of biological responses in eukaryotic cells, including cytoskeletal dynamics, cell motility and cell cycle progression. In the present review, we summarize our current understanding of the role of Rho proteins in cell cycle control, highlighting the contribution of specific members of the Rho family and their downstream targets to the regulation of key elements from the core cell cycle machinery, mostly involved in the G1/S transition.     

Prognostic implications of cyclin B1, p34cdc2, p27(Kip1) and p53 expression in gastric cancer

PURPOSE: Cell cycle progression is regulated by interactions of specific cyclins and cyclin dependent kinases (CDKs) at the G1-S and G2-M checkpoints and cell cycle deregulation plays a major role in carcinogenesis of human cancers. PATIENTS AND METHODS: To investigate the role of cell cycle regulators in the pathogenesis and progression of human gastric cancers, 23 cases of gastric carcinomas were examined for the expression of cyclin B1, p34cdc2, p27(Kip1) and p53 by immunohistochemical methods, and gene expression was correlated with various clinicopathologic findings. RESULTS: Out of 23 cases studied, cyclin B1 was diffusely expressed in 20 cases (87.0%), p34cdc2 in 14 cases (60.9%) and p53 in 12 cases (52.2%), whereas in normal gastric tissues, cyclin B1 and p34cdc2 were weakly expressed and p53 was not expressed. In contrast, p27(Kip1) was expressed in only 8.7% of gastric carcinomas compared with 78.3% of normal gastric tissues. There was correlation between the expression of cyclin B1 and expression of p34cdc2 (p=0.002), between the expression of cyclin B1 and loss of p27(Kip1) (p=0.025), and between the expression of p34cdc2 and loss of p27(Kip1) (p=0.065). In addition, expression of cyclin B1 was correlated with regional lymph node metastasis (p=0.032). CONCLUSION: Our results indicate that cyclin B1 and p34cdc2 are involved in the genesis or progression of gastric cancers. Furthermore, overexpression of cyclin B1 may play an important role in lymph node metastatic potential of gastric cancer. Thus, abnormal expression of cyclin B1 and CDKs, overexpression of p53 and loss of p27(Kip1) expression may play important roles in human gastric carcinogenesis.     

p27Kip1反义寡核苷酸对B淋巴瘤细胞WEHI-231细胞周期的影响

目的　探讨p2 7Kip1在抗原受体介导的B淋巴瘤细胞WEHI- 2 31细胞周期停止信号中的作用。方法　用抗IgM抗体诱导WEHI- 2 31细胞细胞周期停止。用合成的p2 7Kip1反义寡核苷酸抑制p2 7Kip1基因的表达。采用流式细胞仪 ,分析细胞核的DNA含量和细胞周期的变化。用体外激酶实验检测Cdk2的活性 ,Westernblot检测Rb蛋白的磷酸化水平。结果　合成的p2 7Kip1反义寡核苷酸能阻断抗IgM抗体诱导的p2 7Kip1基因表达的上调。用p2 7Kip1反义寡核苷酸处理WEHI-2 31细胞 ,可恢复抗原受体交联引起的周期素依赖性激酶Cdk2活性的降低 ,以及Rb蛋白磷酸化水平的下降 ,并使细胞周期恢复运转。结论　p2 7Kip1可能在抗原受体信号介导的WEHI-2 31细胞的细胞周期停止中发挥主要作用     

Altered expression of p27Kip1‐interacting cell‐cycle regulators in the adult testicular germ cell tumors: potential role in tumor development and histological progression

We examined the potential role of cell‐cycle dysregulation in the development and histological progression of adult testicular germ cell tumors (TGCTs). Expressions of p27^Kip1‐interacting cell‐cycle regulators (down‐regulation of p27^Kip1 and overexpression of Skp2, Cks1, cyclin A, and cyclin E) and Ki‐67 labeling index (LI) were immunohistochemically examined in histological components of 50 intratubular germ cell neoplasms, unclassified (IGCNUs); 74 seminomas; and 25 embryonal carcinomas, identified from 88 patients. Altered expression of p27^Kip1, Skp2, Cks1, cyclin A, and cyclin E was observed in 20%, 12%, 16%, 10%, and 24% of IGCNUs; 26%, 36%, 27%, 89%, and 23% of seminomas; and 48%, 68%, 56%, 100%, and 60% of embryonal carcinomas, respectively. A significant difference in the frequency of Skp2 and cyclin A overexpression was observed between IGCNUs and seminomas. Significantly more frequent alterations of Skp2, Cks1, and cyclin E and p27^Kip1 were detected in embryonal carcinomas than in seminomas. Alterations of all cell‐cycle regulators were significantly more frequent in embryonal carcinomas than in IGCNUs. The mean Ki‐67 LI significantly increased from IGCNU (21.2%) through seminoma (34.7%) to embryonal carcinoma (54.2%). These results suggest that alterations of the p27^Kip1‐interacting cell‐cycle regulators are common in TGCTs and may be involved in their histological progression.     

肾癌中cyclinD1和p27kip1的表达及其意义

目的探讨cyc lin D1、p27k ip1在普通型肾细胞癌(renal cell carc inom a,RCC)发生、发展中的作用。方法用半定量RT-PCR方法检测25例普通型RCC和10例肿瘤远端的正常肾组织中cyc lin D1的mRNA含量,用免疫组化方法检测76例普通型RCC中cyc lin D1和p27k ip1蛋白的表达,并对cyc lin D1、p27k ip1蛋白表达与临床病理参数的关系进行分析。结果普通型RCC中cyc lin D1的mRNA含量0.488±0.399,高于正常对照组0.089±0.066(P<0.01)。cyc lin D1的表达与肿瘤体积大小有关,体积大者cyc lin D1高表达(P<0.05)。普通型RCC中p27k ip1表达低于正常对照组,随着p27k ip1表达的降低,肿瘤的细胞核Fu-hrm an分级、TNM分期增高。结论cyc lin D1高表达和p27k ip1的低表达与普通型RCC的发生有关;p27k ip1的低表达可能促进肿瘤的演进,p27k ip1的表达可作为评价普通型RCC预后的参考指标。     

p27~(Kip1)调控永生化人神经前体细胞分化的机制

目的研究p27Kip1在永生化人神经前体细胞分化中的作用,探讨神经前体细胞的分化机制。方法取本课题组已建立的永生化人神经前体细胞系hSN12W-TERT细胞(第12代)进行培养,在细胞进入对数生长期时给予1μmol/L全反式视黄酸(RA)诱导,重复诱导3次,每次均在诱导的第3、5、7天收集细胞,用流式细胞仪分析RA诱导第3天细胞周期的变化,用免疫印迹法检测RA诱导第3、5、7天p27Kip1、p21cip1细胞周期蛋白依赖激酶2(cdk2)及S期激酶相关蛋白2(skp2)的变化。结果流式细胞术结果显示,hSN12W-TERT细胞经1μmol/LRA诱导3d后,G0/G1期细胞的比例由77.25%上升至85.68%,而S期的比例由9.38%下降到8.57%。免疫印迹法结果显示,RA诱导第3天,hSN12W-TERT细胞p27Kip1蛋白表达比未经RA诱导的细胞增加,并在RA诱导第5天达到高峰(P0.05)。未经RA诱导的正常hSN12W-TERT细胞p21Cip1蛋白表达弱,RA诱导后p21Cip1蛋白的表达略呈下降趋势。RA诱导前后hSN12W-TERT细胞cdk2蛋白的表达变化不明显,但反映cdk2活性的磷酸化cdk2(p-cdk2)的表达在RA诱导后明显下降,同时,参与p27Kip1泛素降解途径的重要因子skp2的表达在RA诱导后明显下降。结论在RA诱导hSN12W-TERT细胞分化的过程中,p27Kip1通过抑制cdk2的活性而发挥促细胞分化的作用,且RA诱导后p27Kip1蛋白含量增加与其泛素降解途径被抑制密切相关。     

Localization of p27kip1 in the developing avian retina: Sustained expression in the mature tissue

p27kip1 is a cyclin/CDK inhibitor that is expressed in cells that exit cell cycle and turn post-mitotic. Here, we characterized the expression and localization of p27kip1 during the development of the chick embryo retina. Expression of p27kip1 in this tissue begins at embryonic day 5 (E5), increasing as development proceeds. In contrast to the expression in the developing rat retina that markedly decreases after postnatal day 6, expression of p27kip1 in the chick retina decreases only slightly (30%) after E12. Thereafter, it remains highly expressed in the tissue. p27kip1 expression increases in an orderly succession. By E5, immunoreactivity was observed over β-tubulin III (TUJ-1) positive cell bodies located in the prospective Ganglion Cell Layer. By E7, p27kip1 was also detected over elongated cell nuclei located in the inner and outer portions of the Neuroblastic Layer and over cell bodies in the middle of the Inner Plexiform Layer. By E12, besides labeled cell bodies, labeled processes from amacrine cells and from cells at the GCL in the IPL were identified. In retinas from post-hatched chicken, immunoreactivity was observed over cell bodies located at all nuclear layers. Several differentiated ChAT positive cholinergic cells were labeled for p27kip1. Our data suggest that, as in the retina of other species, p27kip1 is expressed in cells that are exiting cell cycle and differentiating in the early developing chick embryo retina. However, as opposed to rodents and amphibians, neuronal expression of p27kip1 is sustained in the adult chick retina, indicating that its expression is differently regulated during development in this specie.     

Suppressor activity of anergic T cells induced by IL-10-treated human dendritic cells: association with IL-2- and CTLA-4-dependent G1 arrest of the cell cycle regulated by p27Kip1

We have previously shown that human IL-10-treated dendritic cells (DC) induce an antigen-specific anergy in CD4+ T lymphocytes. These anergic T cells are characterized by an inhibited proliferation, a reduced production of IL-2, and additionally display antigen-specific suppressor activity. In this study we investigated the mechanisms underlying the anergic state and regulatory function of these T cells. We did not observe enhanced rates of programmed cell death of anergic CD4+ suppressor T cells compared to T cells stimulated with mature DC. Cell cycle analysis by DNA staining and Western blot experiments revealed an arrest of anergic CD4+ T suppressor cells in the G1 phase. High levels of the IL-2-dependent cyclin-dependent kinase (cdk) inhibitor p27Kip1 were found in anergic CD4+ suppressor T cells resulting in an inhibited activation of retinoblastoma protein and an arrest of cell cycle progression in the G1 phase. Addition of IL-2, but not blocking of the CTLA-4 pathway restored the proliferation of the suppressor T cells. In contrast, both treatments induced a down-regulation of p27Kip1 and acomplete inhibition of the antigen-specific regulatory function as demonstrated by high proliferation and enhanced IFN-gamma production of co-cultured T cells. Further experiments demonstrated that p27Kip-expressing regulatory CD4+CD25+ T cells did not contribute to induction of T cell anergy in this model. Our data show that regulatory function of anergic CD4+ suppressor T cells is associated with an arrest in the G1 phase of the cell cycle mediated by increased levels of the IL-2- and CTLA-4-dependent cdk inhibitor p27Kip1.     

Differential modulation of cyclin-dependent kinase inhibitor p27Kip1 by negative signaling via the antigen receptor of B cells and positive signaling via CD40

The cross-linking of surface immunoglobulins (sIg) of B cells can transmit a negative signal, resulting in cell cycle arrest, apoptosis or both. Signaling via the B cell antigen CD40 reverses the sIg-mediated negative signaling and induces activation and proliferation of B cells. We investigated the molecular mechanisms for cell cycle regulation by negative and positive signaling via sIg and CD40, respectively, by using the B cell line WEHI-231. Cross-linking of sIg almost completely reduced the activity of cyclin-dependent kinase (Cdk) 2, essential for cell cycle progression in the late G1 phase, although the level of Cdk2 was not reduced. Among the factors that regulate Cdk2 activation, the activity of the Cdk-activating kinase (CAK) appeared intact and cyclin E was reduced only partially in sIg-cross-linked WEHI-231. In contrast, sIg cross-linking induced a significant Cdk inhibitor (CKI) activity. Since a 27-kDa protein was co-precipitated with Cdk2 in anti-Ig-treated, but not untreated WEHI-231, and the CKI activity in anti-Ig-treated WEHI-231 was neutralized by anti-p27^Kip1, antibodies, it is most likely that p27^Kip1 is responsible for the CKI activity induced by sIg cross-linking. p27^Kip1 may thus play a role in growth inhibition of B cells by negative signaling via sIg. In contrast, CD40 signaling enhanced Cdk2 activity and reduced the p27^Kip1 level in anti-Ig-treated WEHI-231, suggesting that the reduction of p27^Kip1 plays an important role in the abrogation of sIg-mediated growth arrest by CD40 signaling. Taken together, p27^Kip1 is likely to be a crucial target molecule of the negative signaling via sIg and the positive signaling via CD40 essential for T cell-dependent immune responses.