Expression of cyclin D2 and D3 in lymphoid lesions

The D-type cyclins, involved in the regulation of G1 progression of the cell cycle, are expressed in a lineage-specific manner. Normal hematopoietic cells express cyclin D2 and/or D3. In order to determine whether their expression pattern changes in lymphoid tumors, we examined cyclin D2 and D3 expression in non-neoplastic and neoplastic lymphoid lesions, using a sensitive immunohistochemical amplification method. Centroblasts in lymphoid follicles of reactive lymph nodes expressed exclusively cyclin D3 and no D2. Interfollicular areas contained scattered cyclin D3 and D2 positive cells. By double staining, cyclin D3 was detected in CD79a positive B cells, CD3 positive T cells and CD68 positive macrophages. Cyclin D2 was present only in CD3 positive T cells. Neoplastic lymphoid lesions included 33 B cell lymphomas, 9 T cell lymphomas and 12 Hodgkin's lymphomas. The B cell lymphomas comprised 9 follicular lymphomas (FL), 1 Burkitt lymphoma (BL), 22 diffuse large cell lymphomas (DL) and 1 chronic lymphocytic leukemia (CLL). All 9 FLs and the single BL expressed exclusively cyclin D3, similarly to germinal center B cells, that represent their cells of origin. Six DLs expressed both cyclin D2 and D3, while 6 expressed only D3. Among the 9 pleomorphic T cell lymphomas, medium and large cell type, 5 expressed cyclin D2. Cyclin D3 was also detected in scattered cells in 4 of 9 cases and was highly expressed in 2 of 9 T cell lymphomas. The majority of Hodgkin's lymphomas expressed both cyclin D2 and D3 in Hodgkin/Reed-Sternberg (HRS) cells. The high frequency of positive cells indicates that both cyclins were expressed in the same cells.

Cerebellar histogenesis is disturbed in mice lacking cyclin D2

Formation of brain requires deftly balancing primary genesis of neurons and glia, detection of when sufficient cells of each type have been produced, shutdown of proliferation and removal of excess cells. The region and cell type-specific expression of cell cycle regulatory proteins, such as demonstrated for cyclin D2, may contribute to these processes. If so, regional brain development should be affected by alteration of cyclin expression. To test this hypothesis, the representation of specific cell types was examined in the cerebellum of animals lacking cyclin D2. The loss of this cyclin primarily affected two neuronal populations: granule cell number was reduced and stellate interneurons were nearly absent. Differences between null and wild-type siblings were obvious by the second postnatal week. Decreases in granule cell number arose from both reduction in primary neurogenesis and increase in apoptosis of cells that fail to differentiate. The dearth of stellate cells in the molecular layer indicates that emergence of this subpopulation requires cyclin D2 expression. Surprisingly, Golgi and basket interneurons, thought to originate from the same precursor pool as stellate cells, appear unaffected. These results suggest that cyclin D2 is required in cerebellum not only for proliferation of the granule cell precursors but also for proper differentiation of granule and stellate interneurons.

The proto-oncogene c-myc is a direct target gene of Epstein-Barr virus nuclear antigen 2

Epstein-Barr virus (EBV) infects and transforms primary B lymphocytes in vitro. Viral infection initiates the cell cycle entry of the resting B lymphocytes. The maintenance of proliferation in the infected cells is strictly dependent on functional EBNA2. We have recently developed a conditional immortalization system for EBV by rendering the function of EBNA2, and thus proliferation of the immortalized cells, dependent on estrogen. This cellular system was used to identify early events preceding induction of proliferation. We show that LMP1 and c-myc are directly activated by EBNA2, indicating that all cellular factors essential for induction of these genes by EBNA2 are present in the resting cells. In contrast, induction of the cell cycle regulators cyclin D2 and cdk4 are secondary events, which require de novo protein synthesis.

D-type cyclins in adult human testis and testicular cancer: relation to cell type, proliferation, differentiation, and malignancy

D-type cyclins are proto-oncogenic components of the 'RB pathway', a G1/S regulatory mechanism centred around the retinoblastoma tumour suppressor (pRB) implicated in key cellular decisions that control cell proliferation, cell-cycle arrest, quiescence, and differentiation. This study focused on immunohistochemical and immunochemical analysis of human adult testis and 32 testicular tumours to examine the differential expression and abundance of cyclins D1, D2, and D3 in relation to cell type, proliferation, differentiation, and malignancy. In normal testis, the cell type-restricted expression patterns were dominated by high levels of cyclin D3 in quiescent Leydig cells and the lack of any D-type cyclin in the germ cells, the latter possibly representing the only example of normal mammalian cells proliferating in the absence of these cyclins. Most carcinoma-in-situ lesions appeared to gain expression of cyclin D2 but not D1 or D3, while the invasive testicular tumours showed variable positivity for cyclins D2 and D3, but rarely D1. An unexpected correlation with differentiation rather than proliferation was found particularly for cyclin D3 in teratomas, a conceptually significant observation confirmed by massive up-regulation of cyclin D3 in the human teratocarcinoma cell line NTera2/D1 induced to differentiate along the neuronal lineage. These results suggest a possible involvement of cyclin D2 in the early stages of testicular oncogenesis and the striking examples of proliferation-independent expression point to potential dual or multiple roles of the D-type cyclins, particularly of cyclin D3. These findings extend current concepts of the biology of the cyclin D subfamily, as well as of the biology and oncopathology of the human adult testis. Apart from practical implications for the assessment of proliferation and oncogenic aberrations in human tissues and tumours, this study may inspire further research into the emerging role of the cyclin D proteins in the establishment and/or maintenance of the differentiated phenotypes.

Transcriptional regulation of the cyclin D1 promoter by STAT5: its involvement in cytokine-dependent growth of hematopoietic cells

STAT5 is a member of a family of transcription factors that participate in the signal transduction pathways of many hormones and cytokines. Although STAT5 is suggested to play a crucial role in the biological effects of cytokines, its downstream target(s) associated with cell growth control is largely unknown. In a human interleukin-3 (IL-3)-dependent cell line F-36P-mpl, the induced expression of dominant-negative (dn)-STAT5 and of dn-ras led to inhibition of IL-3-dependent cell growth, accompanying the reduced expression of cyclin D1 mRNA. Also, both constitutively active forms of STAT5A (1*6-STAT5A) and ras (H-rasG12V) enabled F-36P-mpl cells to proliferate without added growth factors. In NIH 3T3 cells, 1*6-STAT5A and H-rasG12V individually and cooperatively transactivated the cyclin D1 promoter in luciferase assays. Both dn-STAT5 and dn-ras suppressed IL-3-induced cyclin D1 promoter activities in F-36P-mpl cells. Using a series of mutant cyclin D1 promoters, 1*6-STAT5A was found to transactivate the cyclin D1 promoter through the potential STAT-binding sequence at -481 bp. In electrophoretic mobility shift assays, STAT5 bound to the element in response to IL-3. Furthermore, the inhibitory effect of dn-STAT5 on IL-3-dependent growth was restored by expression of cyclin D1. Thus STAT5, in addition to ras signaling, appears to mediate transcriptional regulation of cyclin D1, thereby contributing to cytokine-dependent growth of hematopoietic cells.

FLI-1 inhibits differentiation and induces proliferation of primary erythroblasts

Friend virus-induced erythroleukemia involves two members of the ETS family of transcriptional regulators, both activated via proviral insertion in the corresponding loci. Spi-1/PU.1 is expressed in the disease induced by the original Friend virus SFFV(F-MuLV) complex in adult mice. In contrast, FLI-1 is overexpressed in about 75% of the erythroleukemias induced by the F-MuLV helper virus in newborn mice. To analyse the consequences of the enforced expression of FLI-1 on erythroblast differentiation and proliferation and to compare its activity to that of PU.1/Spi-1, we used a heterologous system of avian primary erythroblasts previously described to study the cooperation between Spi-1/PU.1 and the other molecular alterations observed in SFFV-induced disease. FLI-1 was found: (i) to inhibit the apoptotic cell death program normally activated in erythroblasts following Epo deprivation; (ii) to inhibit the terminal differentiation program induced in these cells in response to Epo and; (iii) to induce their proliferation. However, in contrast to Spi-1/PU.1, the effects of FLI-1 on erythroblast, differentiation and proliferation did not require its cooperation with an abnormally activated form of the EpoR. Enhanced survival of FLI-1 expressing erythroblasts correlated with the upregulation of bcl2 expression. FLI-1 also prevented the rapid downregulation of cyclin D2 and D3 expression normally observed during Epo-induced differentiation and delayed the downregulation of several other genes involved in cell cycle or cell proliferation control. Our results show that overexpression of FLI-1 profoundly deregulates the normal balance between differentiation and proliferation in primary erythroblasts. Thus, the activation of FLI-1 expression observed at the onset of F-MuLV-induced erythroleukemia may provide a proliferative advantage to virus infected cells that would otherwise undergo terminal differentiation or cell death.

Bruton's tyrosine-kinase-deficient murine B lymphocytes fail to enter S phase when stimulated with anti-immunoglobulin plus interleukin-4

One of the earliest recognized defects of B cells carrying the xid mutation in the gene encoding for Bruton's tyrosine kinase (Btk) was their inability to proliferate in response to anti-immunoglobulin plus interleukin (IL)-4 stimulation. Previous attempts to define the stage at which this proliferative block occurred using xid B cells provided dissimilar results. We decided to reinvestigate this question using B cells from C57BL/6-Btk-protein-deficient (BtkM) mice. Upon stimulation with anti-IgM and IL-4, BtkM cells increase in size and up-regulate early activation markers such as CD69 and B7-2, however, they do not progress into the cell cycle further than a very early G1 stage. They down-regulate the cyclin-dependent kinase (cdk) inhibitor p27 to some extent but fail to up-regulate the G1-phase cyclins D2 and E and the retinoblastoma protein (pRb) remains hypo-phosphorylated. While approximately 25% of the wild-type cells enter S phase after 36 h stimulation, only 1% of the BtkM cells do so. The proliferative responsiveness of the BtkM cells is restored when the phorbol ester phorbol 12,13-di-butyrate (PDBu) is added to the anti-IgM plus IL-4 cultures. Collectively, our data demonstrate that a dramatically reduced frequency of responsive cells underlies the low proliferation of anti-IgM plus IL-4-stimulated Btk-deficient B cells and point towards an early block in the G1 phase due to inadequate activation of a pathway that regulates PKC activation.

[Effect of composite blood-activating decoction on expression of adherent molecule and cyclin in bone marrow hematopoietic cells in mice of immune-induced aplastic anemia]

OBJECTIVE

To study the effect of composite blood-activating decoction (CBAD) on expression of adherent molecule CD49 d and cyclin D2 in bone marrow hematopoietic cells in experimental immune-mediated aplastic anemia (AA) mice.

METHODS

After the model of AA was established, the animals were fed with 0.2 ml of 100% CBAD, twice a day for 12 days. Te CD49 d and cyclin D2 expression level of bone marrow hematopoietic cells in model mice were measured by flow cytometor analysis system at the 13th day of experiment.

RESULTS

CD49 d expression level in CBAD group was significantly higher than that in the AA group (P < 0.05), and was similar to that in the normal group (P > 0.05). The expression of cyclin D2 in CBAD group was significantly higher than that in the AA group (P < 0.01), but the cell count of G0 + G1 phase was significantly lower in the CBAD group, as compared with the AA group, P < 0.01.

CONCLUSION

CBAD can increase the expression of adherent molecule CD49 d and cyclin D2 in bone marrow hematopoietic cells, and promote the growth of hematopoietic cells.

Rapid and efficient cloning of proviral flanking fragments by kanamycin resistance gene complementation

We have developed a technique for the rapid cloning of unknown flanking regions of transgenic DNA. We complemented a truncated kanamycin resistance gene of a bacterial plasmid with a neomycin resistance gene fragment from a gene transfer vector. Optimized transformation conditions allowed us to directly select for kanamycin-resistant bacteria. We cloned numerous proviral flanking fragments from growth factor-independent cell mutants that were obtained after infection with a replication incompetent retroviral vector and identified integrations into the cyclin D2 and several unknown genomic sequences. We anticipate that our method could be adapted to various vector systems that are used to tag and identify genes and to map genomes.

Effect of ligustrazine on expression of adherent molecule CD49d and cyclin D2 in hematopoietic cells in acute radiation injured mice

After irradiation by 8.0 Gy gamma-ray, each mouse was stomach-fed by 4 mg ligustrazine injection twice a day. On the 7th day after irradiation, CD49d expression in ligustrazine-treated group was significantly higher than that in control group (P < 0.01), and showed no difference from that in normal group (P > 0.05). On the 14th day after irradiation. CD49d expression was increased in control group, but decreased significantly in ligustrazine-treated group (P < 0.01). The expression of Cyclin D2 in spleen mononuclear cells (MNC) in ligustrazine-treated group was significantly higher than that in control group, but the ratio of G0 + G1 phase cells was significantly lower in ligustrazine-treated group (P < 0.01). This finding indicated that ligustrazine could increase the expression of adherent molecule on bone marrow hematopoietic cells and Cyclin D2 in spleen MNC, thereby promoting the growth of hematopoietic cells.

Increased cyclin D1 in vulnerable neurons in the hippocampus after ischaemia and epilepsy: a modulator of in vivo programmed cell death?

Several observations suggest that delayed neuronal death in ischaemia, epilepsy and other brain disorders includes an apoptotic component, involving programmed cell death (PCD). PCD is hypothesized to result, in part, from aberrant control of the cell cycle. Because they are instrumental in mitosis, cyclins D are key markers to evaluate whether neurons indeed progress into the cell cycle in situations of pathology. Therefore, we investigated in rat brains, the expression of cyclins D in the delayed neuronal death that occurs following transient global ischaemia and kainate-induced seizures. Following a four-vessel occlusion insult, quantitative in situ hybridization revealed a highly significant and persistent 100% increase of cyclin D1 mRNA in the vulnerable pyramidal neurons of the CA1 hippocampal region. Ischaemia also induced a smaller and transient cyclin D1 mRNA increase in the resistant CA3 area and dentate gyrus. In contrast, the cyclin D2 and D3 mRNAs, expressed constitutively in the adult rat hippocampus, were not upregulated. Following kainate-induced seizures, cyclin D1 mRNA was induced in the vulnerable CA3 region, and to a lesser extent, in non-vulnerable regions. Cyclin D1 immunohistochemistry revealed increased protein levels in the cytoplasm and nucleus of neurons commited to die after ischaemia. Double labelling experiments indicate that cyclin D1 is also expressed in reactive astrocytes but not in microglial cells. Finally, we report that in neurons, cyclin D1 expression peaks before nuclear condensation and the appearance of DNA fragmentation. We propose that cyclin D1, when expressed at high levels in lesioned neurons, may act as a modulator of apoptosis.

Mechanism of interleukin-10 inhibition of T-helper cell activation by superantigen at the level of the cell cycle

We have analyzed the effects of interleukin-10 (IL-10) on the entry of quiescent CD4(+) T cells into the cell cycle upon stimulation with the superantigen staphylococcal enterotoxin B (SEB). IL-10 arrested cells at G0/G1. IL-10 treatment prevented the downregulation of p27(Kip1), an inhibitory protein that controls progression out of the G0 phase of the cell cycle. IL-10 also prevented the upregulation of the G1 cyclins D2 and D3, proteins necessary for entry and progression through the G1 phase of the cell cycle. Associated with the inhibition of the cell cycle, IL-10 suppressed SEB induction of interleukin-2 (IL-2). Addition of exogenous IL-2 to IL-10-treated cells significantly reversed the antiproliferative effects of IL-10. Moreover, IL-10 effects on the early G1 proteins p27(Kip1) and cyclin D2 were similarly reversed by exogenous IL-2. Although this reversal by IL-2 was pronounced, it was not complete, suggesting that IL-10 may have some effects not directly related to the suppression of IL-2 production. Cell separation experiments suggest that IL-10 can effect purified CD4(+) T cells directly, providing functional evidence for the presence of IL-10 receptors on CD4(+) T cells. IL-10 also inhibited expression of IL-2 transcriptional regulators c-fos and c-jun, which also inhibit other cell functions. Our studies show that the mechanism of IL-10 regulation of quiescent CD4(+) T-cell activation is mainly by blocking induction of IL-2 that is critical to downregulation of p27(Kip1) and upregulation of D cyclins in T-cell activation and entry into the cell cycle.

Cyclin D- and E-dependent kinases and the p57(KIP2) inhibitor: cooperative interactions in vivo

This study examines in vivo the role and functional interrelationships of components regulating exit from the G1 resting phase into the DNA synthetic (S) phase of the cell cycle. Our approach made use of several key experimental attributes of the developing mouse lens, namely its strong dependence on pRb in maintenance of the postmitotic state, the down-regulation of cyclins D and E and up-regulation of the p57(KIP2) inhibitor in the postmitotic lens fiber cell compartment, and the ability to target transgene expression to this compartment. These attributes provide an ideal in vivo context in which to examine the consequences of forced cyclin expression and/or of loss of p57(KIP2) inhibitor function in a cellular compartment that permits an accurate quantitation of cellular proliferation and apoptosis rates in situ. Here, we demonstrate that, despite substantial overlap in cyclin transgene expression levels, D-type and E cyclins exhibited clear functional differences in promoting entry into S phase. In general, forced expression of the D-type cyclins was more efficient than cyclin E in driving lens fiber cells into S phase. In the case of cyclins D1 and D2, ectopic proliferation required their enhanced nuclear localization through CDK4 coexpression. High nuclear levels of cyclin E and CDK2, while not sufficient to promote efficient exit from G1, did act synergistically with ectopic cyclin D/CDK4. The functional differences between D-type and E cyclins was most evident in the p57(KIP2)-deficient lens wherein cyclin D overexpression induced a rate of proliferation equivalent to that of the pRb null lens, while overexpression of cyclin E did not increase the rate of proliferation over that induced by the loss of p57(KIP2) function. These in vivo analyses provide strong biological support for the prevailing view that the antecedent actions of cyclin D/CDK4 act cooperatively with cyclin E/CDK2 and antagonistically with p57(KIP2) to regulate the G1/S transition in a cell type highly dependent upon pRb.

Expressions and activities of cell cycle regulatory molecules during the transition from myocyte hyperplasia to hypertrophy

The role of cell cycle dependent molecules in controlling the switch from cardiac myocyte hyperplasia to hypertrophy remains unclear, although in the rat this process occurs between day 3 and 4 after birth. In this study we have determined (1) cell cycle profiles by fluorescence activated cell sorting (FACS); and (2) expressions, co-expressions and activities of a number of cyclins, cyclin-dependent kinases (CDKs) and CDK inhibitors by reverse transcriptase-polymerase chain reaction (RT-PCR), immunoblotting and in vitro kinase assays in freshly isolated rat cardiac myocytes obtained from 2, 3, 4 and 5-day-old animals. The percentage of myocytes found in the S phase of the cell cycle decreased significantly during the transition from hyperplasia to hypertrophy (5.5, 3.5, 2.3 and 1.9% of cells in 2-, 3-, 4- and 5-day-old myocytes, respectively,P<0.05), concomitant with a significant increase in the percentage of G0/G1 phase cells. At the molecular level, the expressions and activities of G1/S and G2/M phase acting cyclins and CDKs were downregulated significantly during the transition from hyperplasia to hypertrophy, whereas the expressions and activities of G1 phase acting cyclins and CDKs were upregulated significantly during this transition. In addition, p21(CIP1)- and p27(KIP1)- associated CDK kinase activities remained relatively constant when histone H1 was used as a substrate, whereas phosphorylation of the retinoblastoma protein was upregulated significantly during the transition from hyperplasia to hypertrophy. Thus, there is a progressive and significant G0/G1 phase blockade during the transition from myocyte hyperplasia to hypertrophy. Whilst CDK2 and cdc2 may be pivotal in the withdrawal of cardiac myocytes from the cell cycle, CDK4 and CDK6 may be critical for maintaining hypertrophic growth of the myocyte during development.

Proliferation-independent induction of macrophage cyclin D2, and repression of cyclin D1, by lipopolysaccharide

D-type cyclins are induced in response to mitogens and are essential and rate-limiting for G1 phase progression in normal mammalian cells. Macrophages proliferating in response to colony-stimulating factor-1 (CSF-1) express cyclin D1 and to a lesser extent cyclin D2 but not cyclin D3. Previously we showed that the macrophage-activating agent lipopolysaccharide (LPS) blocks CSF-1-induced proliferation and cyclin D1 expression in macrophages. Here we report upon the effect of LPS on expression of cyclin D2 in normal mouse bone marrow-derived macrophages (BMM). Unexpectedly we found that this anti-mitogen raised levels of CSF-1-stimulated cyclin D2 mRNA and protein. Furthermore, LPS alone induced cyclin D2 but not cyclin D1. Inhibition of the MEK/ERK (MAPK/ERK kinase/extracellular signal-regulated kinase) mitogen-activated protein kinase pathway repressed LPS-induced cyclin D2 mRNA, whereas inhibition of the p38 mitogen-activated protein kinase enhanced expression. However, in contrast to cyclin D1, cyclin D2 in bone marrow-derived macrophages did not appear to be regulated by protein kinase A pathways. The present data (a) show elevation of a D-type cyclin in the absence of proliferation, (b) demonstrate inverse regulation of two distinct D-type cyclins under identical conditions, and (c) suggest that cyclin D2 plays a role in macrophage activation by LPS.

Early G1 growth arrest of hybridoma B cells by DMSO involves cyclin D2 inhibition and p21[CIP1] induction

Dimethylsulfoxide (DMSO) was shown to inhibit the proliferation of several B cell lines including Raji, Daudi, and SKW6-CL4 but the mechanisms involved in this growth arrest are still unclear. We show that in 7TD1 mouse hybridoma cells a DMSO-induced reversible G1 arrest involves inactivation of Rb kinases, cyclin D2/CDK4 and cyclin E/CDK2. This occurs by at least three distinct mechanisms. Inhibition of cyclin D2 neosynthesis leads to a dramatic decrease of cyclinD2/CDK4 complexes. This in turn enables the redistribution of p27[KIP1] from cyclin D2/CDK4 to cyclin E/CDK2 complexes. In addition, the simultaneous accumulation of p21[CIP1] entails increasing association with cyclin D3/CDK4 and cyclin E/CDK2. Thus, p21[CIP1] and p27[KIP1], act in concert to inhibit cyclin E/CDK2 activity which, together with CDK4 inactivation, confers a G1-phase arrest.

The 5D4 antibody (anti-cyclin D1/D2) related antigen: cytoplasmic staining is correlated to the progression of gastric cancer

In order to clarify the relationship between cyclin D1 and D2 (CD1/CD2) overexpression and progression, 191 gastric cancer cases (81 early and 110 advanced cancers) were investigated using the 5D4 monoclonal antibody for both CD1/CD2 in immunohistochemistry. 5D4 immunoreactivity was noted in 68 (35.6%) cases, staining being restricted to the nucleus in 27 (14.1%) cases, the cytoplasm in 34 (17.8%) cases, and its presence in both the nucleus and cytoplasm in seven (3.7%). Cases demonstrating cytoplasmic positivity, including both positive cases, were significantly more frequent in advanced cancers (P = 0.010), those having lymph node metastasis (P = 0.004) and cases showing cancer invasion of vessels (P = 0.009), although no relation to histological malignant grading was apparent. In contrast, cases of nuclear positivity behaved no differently from 5D4-negative cases. Statistics showed a trend where survival in patients was worse in the cytoplasm-positive cases than the cytoplasm-negative group. However, multivariate analysis revealed no independent statistical significance in the cytoplasmic positivity of prognosis. Additional studies using DCS-6 antibody for CD1 and C-17 antibody for CD2, suggest that nuclear staining of 5D4 indicates the presence of CD1 but cytoplasmic staining is derived from an antigen that is related to CD2. In conclusion, the present results indicate that the accumulation of CD2 in the cytoplasm may play some role in the progression of gastric cancers but not prognosis; however, CD1 overexpression is not linked to either.

Role of G1 phase cyclins and cyclin-dependent kinases during cardiomyocyte hypertrophic growth in rats

Cell cycle regulatory molecules are implicated in cardiomyocyte hypertrophy. We have investigated protein expression of cyclins A, D1-3, and E and cyclin-dependent kinases (CDKs) 2, 4, 5, and 6 in left ventricular (LV) tissues during the development of LV hypertrophy in rats following aortic constriction (AC). Compared with their expression in sham-operated controls (SH), expression of cyclins D2 and D3 and of CDK4 and CDK6 increased significantly from day 3 to day 21 after AC concomitant with increased LV mass. However, no significant difference was observed for CDK2 or CDK5. Cyclins A, D1, and E were undetectable. In vitro kinase activities of CDK4 and CDK6 increased approximately 70% from day 7 to day 14 in AC myocytes compared with SH myocytes (P < 0.03). Fluorescence-activated cell sorter analysis revealed a G0/G1 to G2/M phase progression in AC myocyte nuclei (22.0 +/- 1.1% in G2/M) by day 7 postoperation compared with progression in SH myocyte nuclei (14.0 +/- 0.8% in G2/M; P < 0.01). Thus an upregulation of certain cell cycle regulators is associated with cardiomyocyte hypertrophy.

Expression of cyclin Ds in relation to p53 status in human breast carcinomas

Cyclin D1 has been reported to be overexpressed in many tumours, including breast carcinomas. Cyclin D1 was first identified as a protooncogene (BCL1/PRAD1), and its overexpression was related to tumour proliferation. The product has also recently been identified as important in mediating cell cycle growth arrest via the p53 pathway in murin fibroblast cell lines. Ninety breast carcinomas previously analysed for p53 status were analysed for amplification of cyclin D1, D2 and D3 genes by Southern blot analysis and for protein expression by immunhistochemistry. In 10 samples gene amplification was detected at the cyclin D1 locus. No gene amplification was detected at the cyclin D2 and D3 loci. Immunoreactivity for cyclin D1 was detected in 38 (42.2%) tumour tissue samples. Fifty samples were immunostained for cyclin D2 and D3. Only 2 samples (4%) showed immunoreactivty for cyclin D2, and 9 samples (18%) for cyclin D3. Cyclin D1 protein overexpression was significantly more often found in tumours with wild type p53 and in tumours with higher grades of differentiation expressing ER. No association was seen between gene amplification of the cyclin D1 gene and p53 status. We conclude there is a relationship between wild type p53 and cyclin D1 protein overexpression in clinical material, indicating that cyclin D1 may be another downstream effector of p53.

Hormone-induced proliferation and differentiation of granulosa cells: a coordinated balance of the cell cycle regulators cyclin D2 and p27Kip1

The proliferation and terminal differentiation of granulosa cells are critical for normal follicular growth, ovulation, and luteinization. Therefore, the in situ localization and hormonal regulation of cell cycle activators (cyclin D1, D2, and D3) and cell cycle inhibitors (p27Kip1 and p21Cip1) were analyzed in ovaries of mice and rats at defined stages of follicular growth and differentiation. Cyclin D2 mRNA was specifically localized to granulosa cells of growing follicles, while cyclin D1 and cyclin D3 were restricted to theca cells. In hypophysectomized (H) rats, cyclin D2 mRNA and protein were increased in granulosa cells by treatment with estradiol or FSH and were increased maximally by treatment with both hormones. In serum-free cultures of rat granulosa cells, cyclin D2 mRNA was rapidly elevated in response to FSH, forskolin, and estradiol, indicating that estradiol as well as cAMP can act directly and independently to increase cyclin D2 expression. The levels of p27Kip1 protein were not increased in response to estradiol or FSH. In contrast, when ovulatory doses of human CG (LH) were administered to hormonally primed H rats to stimulate luteinization, cyclin D2 mRNA and protein were rapidly decreased and undetectable within 4 h, specifically in granulosa cells of large follicles. Also in response to LH, the expression of the cell cycle inhibitor p27Kip1 was induced between 12 and 24 h (p21Cip1 was induced within 4 h) and remained elevated specifically in luteal tissue. A critical role for cyclin D2 in the hormone-dependent phase of follicular growth is illustrated by the ovarian follicles of cyclin D2-/- mice, which do not undergo rapid growth in response to hormones, but do express markers of FSH/LH action, cell cycle exit, and terminal differentiation. Collectively, these data indicate that FSH and estradiol regulate granulosa cell proliferation during the development of preovulatory follicles by increasing levels of cyclin D2 relative to p27Kip1 and that LH terminates follicular growth by down-regulating cyclin D2 concurrent with up-regulation of p27Kip1 and p21Cip1.

Expression of G1-->S transition regulatory molecules in human urothelial cancer

Growth of cancer cells is characterized by accelerated passage through the cell cycle, which is often caused by deregulation of the G1-->S transition. In this study the expression of G1-->S transition regulatory molecules was analyzed in 32 transitional cell carcinoma specimens and fifteen normal tissues obtained by cystectomy or nephroureterectomy of mainly locally advanced tumors, as well as six bladder cancer cell lines. Expression of mRNAs for cyclins D1 and D2 and cyclin-dependent kinases (CDK) 2 and 4 was investigated by quantitative reverse transcription-polymerase chain reaction. Overexpression of cyclin D1 compared to normal mucosa was observed in 3 tumors (9.4%), but in neither of the cell lines. All tumors with overexpression were moderately differentiated (G2) pT1 or pT2 tumors, and thus among the less advanced specimens. Cyclin D2 was not expressed in normal bladder mucosa or in tumors. The expression of CDK4 mRNA varied within the same range in mucosa, tumors, and cell lines. CDK2 mRNA expression varied more strongly and was diminished in individual tumors and in four cell lines. It is concluded that cyclin D1 overexpression can play an important role in the early stage of urothelial tumorigenesis, driving cell proliferation. Ectopic expression of cyclin D2 or amplification of CDK4 does not occur at a significant frequency in urothelial carcinomas. Different expression patterns of cyclin D1 and CDK2 indicate heterogeneity in the mechanisms of G1-->S transition deregulation in individual bladder tumors which may elicit differences in their biological and clinical behavior.

Increased expression of cyclin D2 during multiple states of growth arrest in primary and established cells

Cyclin D2 is a member of the family of D-type cyclins that is implicated in cell cycle regulation, differentiation, and oncogenic transformation. To better understand the role of this cyclin in the control of cell proliferation, cyclin D2 expression was monitored under various growth conditions in primary human and established murine fibroblasts. In different states of cellular growth arrest initiated by contact inhibition, serum starvation, or cellular senescence, marked increases (5- to 20-fold) were seen in the expression levels of cyclin D2 mRNA and protein. Indirect immunofluorescence studies showed that cyclin D2 protein localized to the nucleus in G0, suggesting a nuclear function for cyclin D2 in quiescent cells. Cyclin D2 was also found to be associated with the cyclin-dependent kinases CDK2 and CDK4 but not CDK6 during growth arrest. Cyclin D2-CDK2 complexes increased in amounts but were inactive as histone H1 kinases in quiescent cells. Transient transfection and needle microinjection of cyclin D2 expression constructs demonstrated that overexpression of cyclin D2 protein efficiently inhibited cell cycle progression and DNA synthesis. These data suggest that in addition to a role in promoting cell cycle progression through phosphorylation of retinoblastoma family proteins in some cell systems, cyclin D2 may contribute to the induction and/or maintenance of a nonproliferative state, possibly through sequestration of the CDK2 catalytic subunit.

Differential myeloma cell responsiveness to interferon-alpha correlates with differential induction of p19(INK4d) and cyclin D2 expression

Interferon-alpha (IFN-alpha) has been used as therapy for the treatment of a variety of viral diseases and malignancies including multiple myeloma. The effectiveness of interferon-alpha in treating multiple myeloma, however, has been somewhat variable, and the mechanism(s) accounting for this is not well understood. As a means to examine the basis for the differential effectiveness of this cytokine, we have analyzed IFN-alpha-mediated modulation of the cell cycle in two human myeloma cell lines. These two cell lines, ANBL-6 and KAS-6/1, display dramatically different outcomes in response to this cytokine. Although IFN-alpha inhibited the growth of ANBL-6 cells by blocking cell cycle progression from G0/G1 to S phase, IFN-alpha stimulated cell cycle progression in KAS-6/1 cells. Moreover, the effects of IFN-alpha on cell cycle progression correlated with the phosphorylation status of the retinoblastoma protein. Of interest, IFN-alpha increased cyclin D2 expression and cyclin-dependent kinase activity in the KAS-6/1 cells but not in the ANBL-6 cells. To determine whether the differential effects of IFN-alpha on myeloma cell cycle progression could also result from differences in the expression of cyclin-dependent kinase inhibitors, we examined the effects of IFN-alpha on the induction of cyclin-dependent kinase inhibitors with broad regulatory function (p21 and p27) and those with specificity for G1-associated cyclin-cyclin-dependent kinase complexes (p15, p16, p18, and p19). Although we failed to detect an effect of IFN-alpha on expression levels of p21, p15, p16, or p18, IFN-alpha treatment of the ANBL-6 cell line resulted in induction of p19 expression, whereas it was without effect on the KAS-6/1 cell line. These results suggest that heterogeneity in IFN-alpha-mediated growth effects in myeloma cells correlates with differential induction of cyclin D2 and p19(INK4d) expression.

G1-phase regulators, cyclin D1, cyclin D2, and cyclin D3: up-regulation at gastrulation and dynamic expression during neurulation

Gastrulation in rodents is associated with an increase in the rate of growth and with the start of differentiation within the embryo proper. In an effort to understand the role played by the cell cycle control in these processes, expression of cyclin D1, D2, and D3--three major positive regulators of the G1/S transition--has been investigated by in situ hybrization and RT-PCR. Cyclin D1 and D2 transcripts are first detected in the epiblast at gastrulation, when a proliferative burst occurs, and subsequently in its differentiated derivatives within the embryo proper, indicating that activation of their expression takes place prior to the differentiation of epiblast progenitors. In contrast, cyclin D3 transcript is undetectable in the epiblast itself and its expression is activated exclusively in extraembryonic tissues of both epiblast and trophoblast origin. During neurulation, expression of each cyclin D RNA is dynamically regulated along the anterior-posterior axis. In the hindbrain, cyclin D1 and D2 show distinct segment-specific restricted expression and this pattern is conserved between mouse and chick. These results strongly suggest that D-type cyclins act as developmental regulators.

Interferon-alpha-induced G1 phase arrest through up-regulated expression of CDK inhibitors, p19Ink4D and p21Cip1 in mouse macrophages

The mechanism of cell cycle arrest induced by interferon-alpha (IFN-alpha) was analysed using a mouse macrophage cell line, BAC1.2F5A. IFN-alpha added in media before mid-G1 prohibited cells from entering S phase. The blockage of G1/S transition was associated with diminuition of both cyclin D1/cdk4- and cyclin E/cdk2-associated kinase activities. G1 cyclin-associated kinase activities were down-regulated quickly after the addition of IFN-alpha. Cells treated with IFN-alpha contained excess amounts of cdk inhibitors which down-regulated G1 cyclin/cdk-associated kinase activities in the proliferating cells and this action was counteracted by exogenously-supplied recombinant cyclin D2/cdk4 complexes. In parallel, accumulation of p19Ink4D and p21Cip1, and their attachment to cdks were up-regulated quickly after the addition of IFN-alpha. Expression of p19Ink4D and p21Cip1 was potentiated transcriptionally. We concluded that increased attachment of up-regulated cdk inhibitors including p19Ink4D and p21Cip1 to G1 cyclin/cdk complexes contributed to diminuition of G1 cyclin/cdk-associated kinase activities and resulting G1 phase arrest during the early phase of treatment with IFN-alpha.