Induction of G1 arrest by down-regulation of cyclin D3 in T cell hybridomas

Alendronate sodium induces G1 phase arrest and apoptosis in human umbilical vein endothelial cells by inhibiting ROS-mediated ERK1/2 signaling

Bisphosphonates are potent bone resorption inhibitors, among which alendronate sodium (ALN) is commonly prescribed for most osteoporosis patients, but long-term application of ALN can cause bisphosphonate-related osteonecrosis of jaw (BRONJ), the pathogenesis of which remains unclear. Previous studies have suggested that bisphosphonates cause jaw ischemia by affecting the biological behavior of vascular endothelial cells, leading to BRONJ. However, the impacts of ALN on vascular endothelial cells and its mechanism remain unclear. The purpose of this work is to assess the influence of ALN on human umbilical vein endothelial cells (HUVECs) and clarify the molecular pathways involved. We found that high concentration of ALN induced G1 phase arrest in HUVECs, demonstrated by downregulation of Cyclin D1 and Cyclin D3. Moreover, high concentration of ALN treatment showed pro-apoptotic effect on HUVECs, demonstrated by increased levels of the cleaved caspase-3, the cleaved PARP and Bax, along with decreased levels of anti-apoptotic protein Bcl-2. Further experiments showed that ERK1/2 phosphorylation was decreased. Additionally, ALN provoked the build-up of reactive oxygen species (ROS) in HUVECs, leading to ERK1/2 pathway suppression. N-acetyl-L-cysteine (NAC), a ROS scavenger, efficiently promoted the ERK1/2 phosphorylation and mitigated the G1 phase arrest and apoptosis triggered by ALN in HUVECs. PD0325901, an inhibitor of ERK1/2 that diminishes the ERK1/2 phosphorylation enhanced the ALN-induced G1 phase arrest and apoptosis in HUVECs. These findings show that ALN induces G1 phase arrest and apoptosis through ROS-mediated ERK1/2 pathway inhibition in HUVECs, providing novel insights into the pathogenic process, prevention and treatment of BRONJ in individuals receiving extended use of ALN.

miR-195 targets cyclin D3 and survivin to modulate the tumorigenesis of non-small cell lung cancer

miR-195 has recently been reported to function as a tumor suppressor in various cancers, including non-small cell lung cancer (NSCLC). However, the mechanisms by which miR-195 represses the tumorigenesis of NSCLC cells are not fully understood. We performed a high-throughput screen using an miRNA mimic library and confirmed the identification of miR-195 as a tumor suppressor in NSCLC. We demonstrated that overexpression or induced expression of miR-195 in lung tumors slows tumor growth and that repression of miR-195 accelerates tumor growth. In addition, we found that knockout of miR-195 promotes cancer cell growth. We demonstrated that miR-195 targets cyclin D3 to cause cell cycle arrest at the G1 phase and that miR-195 targets survivin to induce apoptosis and senescence in NSCLC cells. Overexpression of cyclin D3 or survivin reverses the effects of miR-195 in NSCLC cells. Through the analysis of data from The Cancer Genome Atlas, we confirmed that the expression of miR-195 is lower in tumors than in adjacent normal tissues and that low expression of miR-195 is associated with poor survival in both lung adenocarcinoma and squamous cell carcinoma patients. Specifically, we found that BIRC5, which codes for survivin, is upregulated in both adenocarcinoma and squamous cell carcinoma tissues and that high expression of BIRC5 is associated with poor survival in adenocarcinoma, but not squamous cell carcinoma. In addition, the ratio of miR-195 level to BIRC5 level is associated with both recurrence-free and overall survival in lung adenocarcinoma. Our results suggest that the miR-195/BIRC5 axis is a potential target for treatment of lung adenocarcinoma specifically, and NSCLC in general.

Cell cycle arrest caused by MEK/ERK signaling is a mechanism for suppressing growth of antigen-hyperstimulated effector T cells

Suppression of T-cell growth is an important mechanism for establishment of self-tolerance and prevention of unwanted prolonged immune responses that may cause tissue damage. Although negative selection of potentially self-reactive T cells in the thymus as well as in peripheral tissues has been extensively investigated and well documented, regulatory mechanisms to dampen proliferation of antigen-specific effector T cells in response to antigen stimulation remain largely unknown. Thus, in this work, we focus on the identification of growth suppression mechanisms of antigen-specific effector T cells. In order to address this issue, we investigated the cellular and molecular events in growth suppression of an ovalbumin (OVA)-specific T-cell clone after stimulation with a wide range of OVA-peptide concentrations. We observed that while an optimal dose of peptide leads to cell cycle progression and proliferation, higher doses of peptide reduced cell growth, a phenomenon that was previously termed high-dose suppression. Our analysis of this phenomenon indicated that high-dose suppression is a consequence of cell cycle arrest, but not Fas-Fas ligand-dependent apoptosis or T-cell anergy, and that this growth arrest occurs in S phase, accompanied by reduced expression of CDK2 and cyclin A. Importantly, inhibition of MEK/ERK activation eliminated this growth suppression and cell cycle arrest, while it reduced the proliferative response to optimal antigenic stimulation. These results suggest that cell cycle arrest is the major mechanism regulating antigen-specific effector T-cell expansion, and that the MEK/ERK signaling pathway has both positive and negative effects, depending on the strength of antigenic stimulation.

Cyclin Dl expression in B-cell non Hodgkin lymphoma

Disorders of the cell cycle regulatory machinery play a key role in the pathogenesis of cancer. Over-expression of cyclin D1 protein has been reported in several solid tumors and certain lymphoid malignancies, but little is known about the effect of its expression on clinical behavior and outcome in B-cell Non-Hodgkin lymphoma (NHL). In this study, we investigated the expression of cyclin Dl in group of patients with NHL and correlated the results with the clinical and laboratory data. The degree of expression of cyclin Dl protein was evaluated by flow cytometry in a group of NHL patients (n = 46) and in normal control group (n = 10). Cyclin Dl over expression was detected in 10 out of 46 (21.7%) patients; they were 5/5-mantle cell lymphoma (MCL) (100%) and 5/28 large B-cell lymphoma (17.8%). All other NHL subtypes showed normal cyclin D1 expression. The clinical signs (hepatomegaly, splenomegaly and B-symptoms, clinical staging) and laboratory data (hemoglobin, white cell count (WBCs), platelet count, and bone marrow infiltration) were not significantly different between NHL subgroup with cyclin Dl over expression and that with normal cyclin Dl expression. Serum lactic dehydrogenase (LDH) levels and lymphadenopathy were significantly higher in NHL group with cyclin D1 over expression as compared to those without. Also, cyclin D1 over expression is associated with poor outcome of NHL patients. Cyclin Dl over expression was evident among all cases of MCL and few cases of large B-cell lymphoma. Cyclin Dl over expression might be used as adjuvant tool for diagnosis of MCL; has role in NHL biology and is bad prognostic index in NHL.

Degradation of cyclin D3 independent of Thr-283 phosphorylation

Cyclin D3 has been shown to play a major role in the regulation of cell cycle progression in lymphocytes. It is therefore important to understand the mechanisms involved in the regulation of this protein. We have previously shown that both basal and cAMP-induced degradation of cyclin D3 in Reh cells is dependent on Thr-283 phosphorylation by glycogen synthase kinase-3beta (GSK-3beta). We now provide evidence of an alternative mechanism being involved in the regulation of cyclin D3 degradation. Treatment of lymphoid cells with okadaic acid (OA), an inhibitor of protein phosphatases 1 and 2A (PP1 and PP2A), induces rapid phosphorylation and proteasomal degradation of cyclin D3. This degradation is not inhibited by the GSK-3beta inhibitors lithium or Kenpaullone, or by substitution of Thr-283 with Ala on cyclin D3, indicating that cyclin D3 can be degraded independently of Thr-283 phosphorylation and GSK-3beta activity. Interestingly, in vitro experiments revealed that PP1, but not PP2A, was able to dephosphorylate cyclin D3 efficiently, and PP1 was found to associate with His-tagged cyclin D3. These results support the hypothesis that PP1 constitutively keeps cyclin D3 in a stable, dephosphorylated state, and that treatment of cells with OA leads to phosphorylation and degradation of cyclin D3 through inhibition of PP1.

TCR pathway involves ICBP90 gene down-regulation via E2F binding sites

Antigen-induced cell death is essential for function, growth and differentiation of T-lymphocytes through legation of the T cell receptor. Since TCR-induced cell death occurs at late G1 checkpoint of the cell cycle and considering that ICBP90 is critical for G1/S transition, we studied the ICBP90 regulation through the TCR pathway in Jurkat cells. ICBP90 expression was strongly decreased after TCR triggering concomitantly to cyclin D3 and topoisomerase IIalpha expression decreases. Cell stimulation with PMA and/or calcium ionophore A23187 down-regulated ICBP90 expression. The decrease of ICBP90 protein and mRNA expressions was accompanied with cell growth arrest. A luciferase reporter assay demonstrated that activation of TCR pathways inhibit ICBP90 gene promoter activity. Three consensus E2F binding sites (called from E2F-a to E2F-c) were identified in the ICBP90 gene promoter and were subjected to mutations. The E2F-a, located in a highly active promoter fragment, shows a strong positive functional activity in proliferating cells. E2F-a and E2F-c binding sites are involved in the TCR-induced down-regulation of ICBP90 gene transcription. Altogether, our data demonstrate that TCR signaling pathways regulate ICBP90 gene expression through pRb/E2F complex. We propose that ICBP90 down-regulation is a key event in G1 arrest preceding T cell death.

A secreted low-molecular-weight protein from Helicobacter pylori induces cell-cycle arrest of T cells

BACKGROUND & AIMS

Although Helicobacter pylori is recognized by the human immune system, the bacteria are not eliminated and lead to a chronic inflammation of the gastric mucosa.

METHODS

We investigated the interaction of H. pylori with human lymphocytes. T and B lymphocytes were isolated from H. pylori-infected patients and stimulated with anti-CD3/CD28 or interleukin-6.

RESULTS

Proliferation of lymphocytes was abolished on co-incubation with different H. pylori strains (1-5 bacteria/cell) or with protein extracts of culture supernatants. Inhibition of proliferation was independent of known virulence factors. The factor is a protein or protein complex with an apparent molecular weight between 30 and 60 kilodaltons, clearly distinct from VacA. Although antigen-specific activation of T cells (as shown by nuclear factor of activated T cells [NFAT]-activation, interferon-gamma production, and CD25 or CD69 up-regulation) remained intact, cell-cycle analysis showed that S-phase entry of T cells was inhibited completely by H. pylori. Consequently, stimulated T cells arrested in the G1 phase of the cell cycle. Western blot analysis showed markedly reduced phosphorylation of the retinoblastoma protein (pRb), suggesting inhibition of G1 cyclin-dependent kinase activity. In line with this, activities of cyclin D3 and cyclin E were down-regulated, and levels of the cyclin-dependent kinase inhibitor p27Kip1 were increased. Mouse embryonic fibroblasts deficient in p27 showed a decrease in H. pylori-induced inhibition of cell proliferation, suggesting a central role for p27 in mediating H. pylori-induced G1 arrest.

CONCLUSIONS

Induction of cell-cycle arrest in lymphocytes may be of major significance for the chronic persistence of bacteria in the human stomach.

Kinetic assessment of general gene expression changes during human naive CD4+ T cell activation

The consequence of naive CD4+ T cell activation is the differentiation and generation of effector cells. How the engagement of T cell receptors and co-stimulatory receptors leads to profound differential changes is not fully understood. To assess the transcription changes during T cell activation, we developed human T cell specific cDNA microarray gene filters and examined the gene expression profiles in human naive CD4+ T cells for 10 continuous time points during the first 24 h after anti-CD3 plus anti-CD28 (anti-CD3/CD28) stimulation. We report here a global and kinetic analysis of gene expression changes during naive CD4+ T cell activation and identify 196 genes having expression levels that significantly changed after activation. Based on the temporal change, there are 15 genes that changed between 0-1 h (early), 25 genes between 2-8 h (middle) and 156 genes between 16-24 h (late) after stimulation. Further analyses of the functions of those genes indicate their roles in maintenance of resting status, activation, adhesion/migration, cell cycle progression and cytokine production. However, a significant majority of these genes are novel to T cells and their functions in T cell activation require further study. Together, these results present a kinetic view of the gene expression changes of naive CD4+ T cells in response to T cell receptor-mediated activation for the first time, and provide a basis in understanding how the complex network of gene expression regulation is programmed during CD4+ T cell activation.

Evidence for Cyclin D3 as a Novel Target of Rapamycin in Human T Lymphocytes

The immunosuppressant rapamycin has been shown to inhibit G(1)/S transition of the cell cycle. This inhibition is thought to be mediated by maintenance of the threshold levels of cyclin-dependent kinase (CDK) inhibitor p27(Kip1) (p27) and inhibition of p70 s6 kinase (p70(s6k)). However, recent evidence suggests that cells still remain sensitive to rapamycin in the absence of functional p27 or p70(s6k). Here, we show that rapamycin represses cyclin D3 levels in activated human T lymphocytes with no inhibitory effects on cyclin D2. Furthermore, rapamycin elicits similar cyclin D3 modulatory effects in B lymphocytes. The overall effect of rapamycin on cyclin D3 leads to impaired formation of active complexes with Cdk4 or Cdk6 and subsequent inhibition of cyclin D3/CDK kinase activity. Decrease in cyclin D3 protein levels is due to translational repression and not due to attenuated transcription of the cyclin D3 gene. Importantly, stable overexpression of cyclin D3 (2-2.5 fold) in Jurkat T cell transfectants renders them resistant to lower doses (1-10 ng/ml) of rapamycin. These results point to a critical role of cyclin D3 in rapamycin-mediated immunosuppressive effects in T cells and cell cycle regulation in lymphocytes in general.

Characterization of transcriptional regulation during negative selection in vivo

Negative selection is the process whereby immature thymocytes expressing TCRs with high affinity for self-peptide:MHC complexes are induced to undergo apoptosis. The transcriptional events that occur as a result of TCR signaling during negative selection are not well-characterized. Using oligonucleotide arrays, we have identified 33 genes that exhibit changes in RNA levels in CD4(+)CD8(+) thymocytes during negative selection in vivo. Of 18 genes that have been further characterized, 13 are regulated in response to stimulation with Ag or anti-CD3 and anti-CD28 Abs ex vivo, indicating that these genes are regulated independently of activation of the peripheral immune system. These data also support the idea that anti-CD3/CD28-mediated thymocyte apoptosis is a valid model for negative selection in vivo. A detailed examination of the regulation of many of the identified genes in response to treatment with dexamethasone or gamma-radiation or in response to anti-CD3/anti-CD28 stimulation in the presence of pharmacological inhibitors of mitogen-activated protein kinase kinase kinase 1, p38 mitogen-activated protein kinase, phosphatidylinositol 3-kinase, calcineurin, and cyclin-dependent kinase 2 has facilitated the elucidation of a map of the transcriptional events that occur downstream of the TCR. These studies support a model whereby similar signal transduction pathways are activated by stimuli that induce positive and negative selection and are consistent with the idea that the balance between opposing proapoptotic and antiapoptotic pathways determines cell fate. The data presented in this study also suggest that calcineurin functions to amplify TCR signals by promoting sustained increases in the levels of specific transcripts.

Forskolin-mediated G1 arrest in acute lymphoblastic leukaemia cells: phosphorylated pRB sequesters E2Fs

Increased intracellular levels of cAMP, induced by forskolin, lead to permanent G1 arrest of Reh cells. As expected, we observed a rapid dephosphorylation of the retinoblastoma protein (pRB) within 2 hours of forskolin treatment concomitant with reduced activity of the pRB-specific kinases. Interestingly, however, the dephosphorylation of pRB, as well as the inhibition of the kinase activities, was only transient, despite the permanent arrest of cells in G1. Importantly, although the pRB-specific kinases were fully active after 48 hours, pRB became only partially rephosphorylated.

The transient dephosphorylation of pRB could be explained by the transient decrease in the activities of the pRB-specific kinases, but to understand why pRB became only partially rephosphorylated, despite fully activated kinases,we postulated that cAMP could activate a pRB-directed phosphatase. It was therefore interesting to find that the phosphatase inhibitor, tautomycin, was able to abolish the forskolin-mediated dephosphorylation of pRB, without increasing the activities of the pRB-specific kinases.

To understand how Reh cells expressing hyperphosphorylated forms of pRB can remain arrested in G1, we used three different methods to test for the ability of pRB to form functional complexes with the family of E2F transcription factors. As expected, we observed an increased complex formation between E2F-1, E2F-4 and pRB after 2 hours when pRB was in its most dephosphorylated state. Suprisingly, however, prolonged treatment with forskolin, which induced partial rephosphorylation of pRB, in fact further increased the complex formation between the E2Fs and pRB, and this also resulted in reduced E2F-promoter activity in vivo. These data imply that in Reh cells, partially phosphorylated forms of pRB retain the ability to inhibit E2F-promoter activity, and thereby prevent cells from entering into S-phase.

Induction of anergy in Th1 cells associated with increased levels of cyclin-dependent kinase inhibitors p21Cip1 and p27Kip1

Th1 cells exposed to Ag and the G(1) blocker n-butyrate in primary cultures lose their ability to proliferate in Ag-stimulated secondary cultures. The ability of n-butyrate to induce anergy in Ag-stimulated, but not resting, Th1 cells was shown here to be blocked by cycloheximide. Subsequent experiments to delineate the nature of the protein apparently required for n-butyrate-induced Th1 cell anergy focused on the role of cyclin-dependent kinase (cdk) inhibitors p21(Cip1) and p27(Kip1). Normally, entry into S phase by Th1 cells occurs around 24 h after Ag stimulation and corresponds with relatively low levels of both p21(Cip1) and p27(Kip1). However, unlike control Th1 cells, anergic Th1 cells contained high levels of both p21(Cip1) and p27(Kip1) when examined 24 h after Ag stimulation. The increase in p21(Cip1) observed in Ag-stimulated anergic Th1 cells appeared to be initiated in primary cultures. In contrast, the increase in p27(Kip1) observed in these anergic Th1 cells appears to represent a re-expression of the protein much earlier than control cells following Ag stimulation in secondary cultures. The anergic Th1 cells contained functionally active cdk inhibitors capable of inhibiting the activity of both endogenous and exogenous cdks. Consequently, it appears that n-butyrate-induced anergy in Th1 cells correlated with the up-regulation of p21(Cip1) and perhaps the downstream failure to maintain low levels of p27(Kip1). Increased levels of both p21(Cip1) and p27(Kip1) at the end of G(1) could prevent cdk-mediated entry into S phase, and thus help maintain the proliferative unresponsiveness found in the anergic Th1 cells.

Activation-induced T cell death occurs at G1A phase of the cell cycle

Peripheral negative selection of cycling T cells after TCR engagement and deletion of activated T cells after an immune response occur by an apoptotic process termed activation-induced cell death (AICD). The cross-linking of TCR-CD3 complex with anti-CD3 monoclonal antibody led to significant apoptotic cell death in peripheral blood T cells. To further define cell cycle restriction points for triggering AICD in T cells, we evaluated the association between cell cycle progression and death signal transduction. Simultaneous DNA / RNA quantification analysis revealed that T cells entering G1A phase of the cell cycle may acquire sensitivity to AICD. The activation of caspase-3 was induced when T cells entered G1A phase. Up-regulation of cyclin-dependent kinases (Cdk4 and Cdk6) and cyclin D3 was initiated in TCR-stimulated T cells entering G1A phase and expression of these markers steadily increased as T cells progressed from G1A into G1B phase. Interestingly, caspase-3 inhibitors could inhibit the up-regulation of these G1 cell cycle regulators and induce G0 / G1A arrest as well as the inhibition of AICD. On the basis of these results, AICD signals are most likely transduced into TCR-stimulated T cells entering G1A phase. T cells that fail to progress from G1A into G1B phase undergo AICD.

Cyclin D3 regulates proliferation and apoptosis of leukemic T cell lines

Activation of the T cell receptor in leukemic T cell lines or T cell hybridomas causes growth inhibition. A similar growth inhibition is seen when protein kinase C is activated through addition of phorbol myristate acetate. This inhibition is due to an arrest of cell cycle progression in G(1) combined with an induction of apoptosis. Here we have investigated the mechanism by which these stimuli induce inhibition of proliferation in Jurkat and H9 leukemic T cell lines. We show that expression of cyclin D3 is reduced by each of these stimuli, resulting in a concomitant reduction in cyclin D-associated kinase activity. This reduction in cyclin D3-expression is crucial to the observed G(1) arrest, since ectopic expression of cyclin D3 can abrogate the G(1) arrest seen with each of these stimuli. Moreover, ectopic expression of cyclin D3 also prevents the induction of programmed cell death by phorbol myristate acetate and T-cell receptor activation, leading us to conclude that cyclin D3 not only plays a crucial role in progression through the G(1) phase, but is also involved in regulating apoptosis of T cells.

Sustained Activation of the Raf-MEK-ERK Pathway Elicits Cytokine Unresponsiveness in T Cells

Activation of T cells via the TCR and other costimulatory receptors triggers a number of signaling cascades. Among them, the Ras-activated Raf-mitogen-activated protein/extracellular signal-related kinase (ERK) kinase (MEK)-ERK signaling cascade has been demonstrated to be crucial for both T cell development and activation. It has previously been demonstrated that high doses of Ag or anti-CD3 mAb are able to induce in T cells a nonresponsive state to subsequent treatment with cytokines such as IL-2. The precise biochemical mechanisms underlying this effect are not fully characterized. In this study, we demonstrate that cytokine nonresponsiveness is accompanied by the induction of the cyclin-dependent kinase inhibitor p21Cip1 that is mediated, at least in part, by the activation of the Raf-MEK-ERK pathway. Furthermore, we demonstrate that selective activation of the Raf-MEK-ERK signaling pathway in T cells is sufficient to induce cytokine nonresponsiveness in both a T cell clone and naive primary T cells. In this case, nonresponsiveness is accompanied by the induction of p21Cip1 and the prevention of p27Kip1 down-regulation, leading to inhibition of cyclin E/cyclin-dependent kinase 2 activity. These data suggest that anti-CD3 mAb-induced cytokine nonresponsiveness may be a consequence of hyperactivation of the Raf-MEK-ERK pathway, leading to alterations in the expression of key cell cycle regulators. These observations may provide a novel insight into the mechanisms of induction of peripheral tolerance.

Inhibition of interleukin 2 signaling and signal transducer and activator of transcription (STAT)5 activation during T cell receptor-mediated feedback inhibition of T cell expansion

Limitation of clonal expansion of activated T cells is necessary for immune homeostasis, and is achieved by growth arrest and apoptosis. Growth arrest and apoptosis can occur passively secondary to cytokine withdrawal, or can be actively induced by religation of the T cell receptor (TCR) in previously activated proliferating T cells. TCR-induced apoptosis appears to require prior growth arrest, and is mediated by death receptors such as Fas. We tested whether TCR religation affects T cell responses to interleukin (IL)-2, a major T cell growth and survival factor. TCR ligation in activated primary human T cells blocked IL-2 induction of signal transducer and activator of transcription (STAT)5 DNA binding, phosphorylation of STAT5, Janus kinase (Jak)1, Jak3, and Akt, and kinase activity of Jak1 and Jak3. Inhibition was mediated by the mitogen-activated protein kinase kinase (MEK)-extracellular stimulus-regulated kinase (ERK) signaling pathway, similar to the mechanism of inhibition of IL-6 signaling we have described previously. TCR ligation blocked IL-2 activation of genes and cell cycle regulatory proteins, and suppressed cell proliferation and expansion. These results identify TCR-induced inhibition of IL-2 signaling as a novel mechanism that underlies antigen-mediated feedback limitation of T cell expansion, and suggest that modulation of cytokine activity by antigen receptor signals plays an important role in the regulation of lymphocyte function.

Type I interferons (IFNs) regulate tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) expression on human T cells: A novel mechanism for the antitumor effects of type I IFNs

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is a proapoptotic member of the TNF family of type II membrane proteins, which constitutes one component of T cell cytotoxicity. In this study, we investigated the expression and function of TRAIL in human peripheral blood T (PBT) cells. Although freshly isolated PBT cells did not express a detectable level of TRAIL on their surface, a remarkable TRAIL expression was rapidly induced on the surface of both CD4(+) and CD8(+) PBT cells upon stimulation with anti-CD3 monoclonal antibody and type I interferons (IFNs). This enhancement of TRAIL expression was a unique feature of type I IFNs (IFN-alpha and IFN-beta), and neither type II IFN (IFN-gamma) nor various other cytokines enhanced TRAIL expression on anti-CD3-stimulated PBT cells. Type I IFNs have been used for clinical treatment of renal cell carcinomas (RCCs), and we found that most RCC cell lines were susceptible to TRAIL-induced apoptosis. Type I IFNs substantially augmented cytotoxic activity of anti-CD3-stimulated PBT cells against RCC cell lines in a TRAIL-dependent manner. These results indicate a unique feature of type I IFNs to regulate TRAIL-mediated T cell cytotoxicity, which may be involved in the antitumor effects of type I IFNs against various tumors.

Laminin 5 promotes activation and apoptosis of the T cells expressing alpha3beta1 integrin

By introducing an alpha3 gene-containing plasmid into a human T cell line Jurkat, we prepared the T cells, which express a high level of the alpha3beta1 integrin, to assess the role of laminin 5 in the skin immune system. The alpha3beta1-expressing T cells adhered to laminin 5 and exhibited spreading. These adhered T cells showed a significant tyrosine phosphorylation of intracellular proteins including p59(fyn) upon T-cell receptor (TCR) stimulation. Six hours after cross-linking TCR, these cells on laminin 5 secreted a three times higher level of IL-2 than those on a BSA-coated plate. Twenty hours after the stimulation, 48% of the alpha3beta1-expressing T cells on laminin 5 caused apoptosis. The protein level of cyclin D3 and E decreased, while that of p53 increased in these T cells. These data suggest that laminin 5 may play at least two regulatory roles for T cell functions: augmentation of IL-2 production by antigen-stimulated T cells and induction of apoptosis in these T cells.

Cyclin D expression is controlled post-transcriptionally via a phosphatidylinositol 3-kinase/Akt-dependent pathway

Cyclin D expression is regulated by growth factors and is necessary for the induction of mitogenesis. Herbimycin A, a drug that binds to Hsp90, induces the destruction of tyrosine kinases and causes the down-regulation of cyclin D and an Rb-dependent growth arrest in the G1 phase of the cell cycle. We find that the induction of D-cyclin expression by serum and its repression by herbimycin A are regulated at the level of mRNA translation. Induction of cyclin D by serum occurs prior to the induction of its mRNA and does not require transcription. Herbimycin A repression is characterized by a decrease in the synthetic rate of D-cyclins prior to changes in mRNA expression and in the absence of changes in the half-life of the protein. This effect on D-cyclin translation is mediated via a phosphatidylinositol 3-kinase (PI 3-kinase)-dependent pathway. PI 3-kinase inhibitors such as wortmannin and LY294002, and rapamycin, an inhibitor of FRAP/TOR, cause a decline in the level of D-cyclins, whereas inhibitors of mitogen-activated protein kinase kinase and farnesyltransferase do not. Cells expressing the activated, myristoylated form of Akt kinase, a target of PI 3-kinase, are refractory to the effects of herbimycin A or serum starvation on D-cyclin expression. These data suggest that serum induction of cyclin D expression results from enhanced translation of its mRNA and that this results from activation of a pathway that is dependent upon PI 3-kinase and Akt kinase.

A Pivotal Role of Cyclin D3 and Cyclin-Dependent Kinase Inhibitor p27 in the Regulation of IL-2-, IL-4-, or IL-10-Mediated Human B Cell Proliferation

The functional differences between IgDhighCD38− naive and IgD−CD38− memory (M) or IgDlowCD38+ germinal center (GC) B cells may stem from their variable response to signals that regulate activation, proliferation, and differentiation. In this report, we provide evidence for differential induction of cell cycle regulators in tonsillar human B cell subpopulations that were activated with anti-IgM and anti-CD40 in the presence or absence of IL-2, IL-4, or IL-10. Naive (IgDhigh) B cells exhibited a significant proliferative response to IL-4, but not to IL-2 or IL-10, whereas these cytokines triggered variable levels of growth in the combined GC/M subpopulation (referred to as IgDlow), as measured by [3H]thymidine incorporation. Induction of growth by cytokines in B cell subpopulations strictly correlated with the increased levels of cyclin D3 and cyclin-dependent protein kinase (cdk) 6. Moreover, only cyclin D3/cdk6 complexes were functional as observed in both naive and GC/M B cells stimulated in the presence of IL-4. In addition, active growth was associated with cytokine-mediated elimination of the cell cycle inhibitor p27. The significance of p27 in human B cell cycle was further demonstrated by rapamycin-mediated growth inhibition of IL-4-dependent proliferation, which resulted in strikingly increased p27 levels. Taken together, our findings suggest that cyclin D3, cdk6, and p27 play key roles in IL-2-, IL-4-, and IL-10-mediated human B cell proliferation. Furthermore, these results may provide a molecular basis for different cycling characteristics of naive and GC/M B cell subpopulations.

Mammalian Polycomb group genes are categorized as a new type of early response gene induced by B-cell receptor cross-linking

Polycomb group (PcG) genes were initially described in Drosophila melanogaster as regulators of the homeobox gene. Four mammalian homologues, mel-18, bmi-1, M33 and rae-28, are analyzed in this study. They not only regulate mammalian homeotic genes by analogy with their Drosophila counterparts, but also have some influence on the growth and differentiation of B lymphocytes. Here we report that these four mammalian PcG genes are rapidly induced after antigen-receptor cross-linking in B cells. Thus we would like to propose that mammalian PcG genes can be categorized as a new type of immediate early gene.

Cyclin D3 expression in normal, reactive and neoplastic tissues

Cyclin D3 immunohistochemical expression was investigated in normal, reactive, and neoplastic human embryonal and adult tissues. In the fetus, cyclin D3 was expressed in selected developmental phases of a limited number of cell systems. In normal adult tissues, cyclin D3 showed two patterns of distribution: in lymphoid tissues it was expressed in proliferative compartments, while in most other tissues it was expressed by terminally differentiated/quiescent cells. This dual role in proliferation and differentiation was partially conserved in neoplasms. In non-Hodgkin lymphomas, cyclin D3 immunolabelling was correlated with proliferative activity and progression; a significant exception was seen in cyclin D1-positive mantle cell lymphomas, which were cyclin D-negative. Benign endocrine tumours were frequently strongly cyclin D3-positive, while high-grade (small cell) neuroendocrine carcinomas were always negative. In most other epithelial neoplasms, cyclin D3 immunostaining was heterogeneous. In breast carcinomas, no relationship was seen between ER status and MIB1 labelling; cyclins D3 and D1 were frequently expressed in the same tumour, while occasional tumours showed an inverse quantitative relationship between cyclins D1 and D3, and rare tumours were negative for both. In soft tissue neoplasms, cyclin D3 was consistently expressed in some tumours, such as stromal tumours of the gastrointestinal tract and embryonal rhabdomyosarcomas. Our data suggest that cyclin D3 has a dual role in proliferation and differentiation in normal tissues and in some neoplastic conditions; that the cyclin D3 expression pattern is different from cyclin D1, suggesting non-redundant functions; that cyclin D3 expression is strong in endocrine cells secreting steroid hormones, and in their neoplastic counterparts; and that cyclin D3 deregulation may be of pathogenetic relevance in lymphomagenesis and could be diagnostically useful.

cDNA cloning, expression, subcellular localization, and chromosomal assignment of mammalian aurora homologues, aurora-related kinase (ARK) 1 and 2

Chromosomal segregation during mitosis as well as meiosis is considered to be regulated by multiple kinases, but the precise mechanism remains largely unknown. A mutation in Drosophila, designated aurora, was identified as a responsible gene for a chromosomal segregation defect and encodes a putative serine-threonine kinase. Here we have identified mammalian aurora homologues, designated aurora-related kinase (ARK) 1 and ARK2. Kinase domains of murine ARK1 and ARK2 showed 61 and 62% identity, respectively, to that of aurora at the amino acid levels, respectively. Cell cycle analysis revealed that the expression of ARK1 was correlated with G2/M phase, while ARK2 was expressed during S and G2/M phases. Immunofluorescence analysis demonstrated that ARK2 was mainly localized to the midbody, while ARK1 has been reported to be localized to the spindle pole during mitosis. Collectively, these results suggest that these two kinases may have distinct roles with different expression timing and subcellular localization during the cell cycle progression. Interspecific backcross mapping revealed that Ark1 is located in a distal region of mouse chromosome 2, while Ark2 is located in a central region of mouse chromosome 11.

Cyclin D1 Expression in Mantle Cell Lymphoma Is Accompanied by Downregulation of Cyclin D3 and Is Not Related to the Proliferative Activity

The cell cycle regulatory protein cyclin D1 is essential for G1-S phase transition in several epithelial and mesenchymal tissues but is apparently not essential in normal mature B cells. An overexpression of cyclin D1 is induced by the chromosomal translocation t(11; 14)(q13; q32), which characterizes non-Hodgkin's lymphomas (NHLs) of mantle cell type. We studied 26 cases of mantle cell lymphoma (MCL) for the expression of cyclins D1 and D3. A total of 23 lymphomas showed a nuclear staining for cyclin D1, whereas reactive B cells of residual germinal centers were constantly negative. When compared with cyclin D3, an inverse staining pattern emerged. Whereas the B cells of residual germinal centers reacted strongly positive for cyclin D3, there was low or missing expression of cyclin D3 in MCL cells. In other B-cell lymphomas (n = 55), including chronic lymphocytic leukemia, low-grade lymphomas of mucosa-associated lymphatic tissue, follicular lymphomas, and diffuse large B-cell lymphomas, no cyclin D1 expression could be detected and 89% of these cases displayed cyclin D3 positivity. Lymphoma cell lines harboring the t(11; 14) showed cyclin D1 protein but no or very low levels of cyclin D3; three other B-cell lines, a T-cell line, and peripheral blood lymphocytes strongly expressed cyclin D3 and reacted negatively for cyclin D1. We conclude that the chromosomal translocation t(11; 14) leads to an abnormal protein expression of cyclin D1 in the tumor cells of MCL and induces a consecutive downregulation of cyclin D3. In contrast to other B-NHLs, cyclin D1 and D3 expression in MCL is not related to the growth fraction.

Induction of interleukin-2 unresponsiveness and down-regulation of the JAK-STAT system upon activation through the T cell receptor

Full activation of T cells with antigen (Ag) and antigen-presenting cells initiates effector functions and proliferation. When T cells are re-stimulated through the T cell receptor (TCR) after a primary stimulation with Ag, growth arrest and cell death are induced. Activation of a T cell clone by cross-linking of TCR induces interleukin (IL)-2 unresponsiveness and ultimately cell death. While the proliferative signal delivered by IL-2 induces c-myc, bcl-2 and cyclin D3 expression, the expression of bcl-2 and cyclin D3 is completely suppressed upon TCR stimulation. Furthermore, TCR stimulation induces a decrease in the protein levels of JAK3 and STAT5, suggesting that IL-2 unresponsiveness and growth arrest of T cells result from down-regulation of JAK3 and STAT5.

Interferon gamma production by natural killer (NK) cells and NK1.1+ T cells upon NKR-P1 cross-linking

Natural killer (NK) cells play an important role in immune response by producing interferon gamma (IFN-gamma) as well as exhibiting cytotoxic function. IFN-gamma produced by NK cells has been suggested to be involved in differentiation of T helper cells. On the other hand, the NKR-P1 molecule was recently identified as one of the important NK cell receptors, and it recognizes certain kinds of oligosaccharides on target cells and triggers NK cells for cytotoxicity. In the present study, we found that NK cells produce great amounts of IFN-gamma upon cross-linking of the NKR-P1 molecule. In contrast, stimulation of NK cells with IL-2 induced proliferation without producing IFN-gamma. Similar to NK cells, NK1.1+ T cells also produced IFN-gamma upon NKR-P1 cross-linking. NK1.1+ T cells produced IFN-gamma but not interleukin 4 (IL-4) upon NKR-P1 cross-linking, whereas they secreted both IFN-gamma and IL-4 upon T cell receptor cross-linking. These results indicate that NKR-P1 is a receptor molecule on NK and NK1.1+ T cells that induces not only cytotoxicity but also IFN-gamma production. Our findings provide a new pathway for IFN-gamma production by NK and NK1.1+ T cells through NKR-P1 molecules; it may be essential for immune regulation.