Human and mouse cyclin D2 splice variants: transforming activity and subcellular localization

We have previously reported the identification of a novel 17 kDa truncated isoform of the cyclin D2 activated in 13% of the leukemias induced by the Graffi murine leukemia retrovirus. Retroviral integration in the Gris1 locus causes an alternative splicing of the mouse cyclin D2 gene and expression of a truncated protein of 159 amino acids that is detected at high levels in the Gris1 tumors and also in normal mouse tissues mainly the brain and ovaries. A truncated form of the cyclin D2 was also found in human. We show here that both mouse- and human-truncated cyclin D2 are able to transform primary mouse embryo fibroblasts (MEF) when co-expressed with an activated Ras protein. The truncated cyclin D2 localizes only to the cytoplasm of transfected cells. It has retained the ability to interact with cyclin-dependent kinases (CDKs), although it is a poor catalyst of pRb phosphorylation. Interestingly, the presence of a similar, alternatively spliced cyclin D2 mRNA was also detected in some human brain tumors.

Differential effects of overexpression of two forms of ephrin-A5 on neonatal rat cardiomyocytes

Eph receptors constitute the largest family of receptor tyrosine kinases. Multiple transcripts of ephrin-A5, the cognate ligand of the EphA3 receptor, were found in neonatal rat cardiomyocytes. Two cDNA clones encoding the full-length ephrin-A5 (ephrin-A5 alpha) and a 27-amino acid deletion form (ephrin-A5 beta) were isolated. To examine the role of ephrin-A5 in cardiomyocytes, the cDNAs were inserted into adenoviral vectors, termed Ad.ephrin-A5 alpha and Ad.ephrin-A5 beta, respectively, and overexpressed in cardiomyocytes. The effect of ephrin-A5 on cardiomyocyte gene expression was investigated using a cDNA expression array and Western blot analysis. The results showed that both ephrin-A5 alpha and ephrin-A5 beta downregulated cyclin D2, cyclin-dependent kinase-4 proteins, and their cognate receptor EphA3, which were associated with reduced bromodeoxyuridine incorporation in cardiomyocytes. Whereas ephrin-A5 alpha and ephrin-A5 beta also induced differential gene expression, only ephrin-A5 beta significantly upregulated the transcription of brain natriuretic peptide and downregulated ras-related protein RAB2, protein kinase C inhibitor protein-1, clusterin, and insulin-like growth factor-binding protein. The results suggest that the two forms of ephrin-A5 share similar function while differ in regulating different sets of genes in cardiomyocytes.

Mechanisms of cell cycle arrest in response to TGF-beta in progestin-dependent and -independent growth of mammary tumors

TGF-beta1 modulation of cell cycle components was assessed in an experimental model in which the synthetic progestin medroxyprogesterone acetate (MPA) induced mammary tumors in Balb/c mice. TGF-beta1 inhibited both MPA-induced proliferation of progestin-dependent C4HD epithelial cells and proliferation of the progestin-independent variant cell type C4HI, arresting cells in G(1) phase of the cell cycle. Progestin-independent 60 epithelial cells evidenced reduced response to TGF-beta1 antiproliferative effects. TGF-beta1 inhibition of cyclins D1 and A expression and up-regulation of p21(CIP1) levels were the common findings in all three cell types. In addition, a significant content reduction of cyclin D1/cdk4 and cyclin A/cdk2 complexes was found after TGF-beta1 inhibition of MPA-dependent and -independent proliferation. TGF-beta1 inhibited cyclin D2 expression and up-regulated p27(KIP1) levels only when acting as inhibitor of MPA-induced proliferation of C4HD cells. Regulation of these two cell cycle components resulted in decreased cyclin D2/cdk2 complex and in increased p27(KIP1) association with cdk2 in C4HD cells treated with TGF-beta1. These two molecular mechanisms, unobserved in progestin-independent growth of C4HI or 60 cells, were associated with a significantly higher degree of inhibition of cdk2 kinase activity in C4HD cells compared to that found in TGF-beta-treated C4HI or 60 cells. Reduced sensitivity of 60 cells to the growth-inhibitory effects of TGF-beta1 correlated with significantly lower levels of p15(INK4B), p21(CIP1), and p27(KIP1) expressed in these cells, compared to the levels present in C4HD or C4HI cells, and correlated as well with lack of expression of p16(INK4). Thus, common targets were found to exist in TGF-beta1 inhibitory action on breast cancer cells, but regulation of specific targets was found when TGF-beta1-inhibited proliferation driven by the progesterone receptor.

In vitro cultured peripheral blood mononuclear cells from patients with chronic schistosomiasis mansoni show immunomodulation of cyclin D1,2,3 in the presence of soluble egg antigens

Infection with Schistosoma mansoni induces a wide range of effects on the immune responses of the host. In the present study we investigated the influence of soluble egg antigens (SEA) on the cell cycle of peripheral blood mononuclear cells (PBMC) from infected and non-infected individuals with S. mansoni resident in an endemic area and blood donors from non-endemic area. The cell cycle, the expression of activation markers and cyclin D(+)(1,2,3) CD3(+) frequency was assessed by flow cytometry. Stimulation of PBMC from infected patients with SEA resulted in a lower frequency of CD3(+) T cells in S phase when compared with the non-infected group. In addition, infected patients presented a decrease of activation marker expression (CD69(+), HLA-DR(+) and CD28(-) on CD4(+) cells and CD25(+), HLA-DR(+) on CD8(+) cells). A reduced frequency was observed of cyclin D(1,2,3) expression in SEA-stimulated T cells from infected individuals when compared with those from the non-infected group. The decreased expression of activation markers and frequency of cyclin D(1,2,3) in T cells may result in arrest of T cells in the G(0)/G(1) phase of the cell cycle, thus explaining the down-regulation observed in chronic schistosomiasis.

High-density growth arrest in Ras-transformed cells: low Cdk kinase activities in spite of absence of p27(Kip) Cdk-complexes

The ras oncogene transforms immortalized, contact-inhibited non-malignant murine fibroblasts into cells that are focus forming, exhibit increased saturation density, and are malignant in suitable hosts. Here, we examined changes in cell cycle control complexes as normal and Ras-transformed cells ceased to grow exponentially, to reveal the molecular basis for Ras-dependent focus formation. As normal cells entered density-dependent arrest, cyclin D1 decreased while cyclin D2 was induced and replaced D1 in Cdk4 complexes. Concomitantly, p27(Kip1) levels rose and the inhibitor accumulated in both Cdk4 and Cdk2 complexes, as these kinases were inactivated. Ras-transformed cells failed to arrest at normal saturation density and showed no significant alterations in cell control complexes at this point. Yet, at an elevated density the Ras-transformed cells ceased to proliferate and entered a quiescent-like state with low Cdk4 and Cdk2 activity. Surprisingly, this delayed arrest was molecularly distinct from contact inhibition of normal cells, as it occurred in the absence of p27(Kip1) induction and cyclin D1 levels remained high. This demonstrates that although oncogenic Ras efficiently disabled the normal response to contact inhibition, a separate back-up mechanism enforced cell cycle arrest at higher cell density.

p27 deficiency cooperates with Bcl-2 but not Bax to promote T-cell lymphoma

The effect of Bcl-2 on oncogenesis is complex and expression may either delay or accelerate oncogenesis. The pro-oncogenic activity is attributed to its well characterized anti-apoptotic function while the anti-oncogenic function has been attributed to its inhibition of cellular proliferation. Recent studies demonstrate that p27 may mediate the effects of Bcl-2 on cellular proliferation. We hypothesized that p27 may suppress tumor formation by Bcl-2 family members. To test this hypothesis, cell cycle inhibition and lymphoma development were examined in Lck-Bcl-2 and Lck-Bax38/1 transgenic mice deficient in p27. Strikingly, p27 deficiency synergistically cooperates with Bcl-2 to increase T cell hyperplasia and development of spontaneous T cell lymphomas. Within 1 year, >90% of these mice had developed thymic T cell lymphomas. This high penetrance contrasts with a one year incidence of <5% of thymic lymphoma in Lck-Bcl-2 or p27 -/- mice alone. In contrast, p27 deficiency had no effect on tumor formation in Lck-Bax38/1 transgenic mice, another model of T cell lymphoma. Histologically the lymphomas in p27 -/- Lck-Bcl-2 mice are lymphoblastic and frequently involve multiple organs suggesting an aggressive phenotype. Interestingly, in mature splenic T cells, Bcl-2 largely retains its anti-proliferative function even in the absence of p27. T cells from p27 -/- Lck-Bcl-2 mice show delayed kinetics of CDK2 Thr-160 phosphorylation. This delay is associated with a delay in the up regulation of both Cyclin D2 and D3. These data demonstrate a complex relationship between the Bcl-2 family, cellular proliferation, and oncogenesis and demonstrate that p27 up-regulation is not singularly important in the proliferative delay observed in T cells expressing Bcl-2 family members. Nonetheless, the results indicate that p27 is a critical tumor suppressor in the context of Bcl-2 expression.

Cell division cycle control in embryonal and alveolar rhabdomyosarcomas

In this study, we investigated the mRNA level of several genes involved in cell cycle regulation in alveolar (ARMS) and embryonal rhabdomyosarcomas (ERMS). p21(Cip1), Cyclin D1, Cyclin D2, Cyclin D3, CDK2, and CDK4 were evaluated by RT-PCR. All (13 out of 13) ERMS expressed the p21(Cip1) gene compared with only 40% (4 out of 10) of the ARMS. Moreover, the amount of p21(Cip1) mRNA was noticeably higher in the ERMS samples than in the positive ARMS specimens. p27(Kip1) protein were analysed by immunohistochemical and immunoblotting. A noticeable difference was observed, in that ERMS had higher amounts of the cell cycle inhibitor compared with the ARMS. Finally, treatment of two rhabdomyosarcoma cell lines, RH-30 and RD, with butyrate, resulted in complete growth inhibition and in the upregulation of the p21(Cip1) and p27(Kip1) levels. Our results demonstrate that ERMS have a much higher level of p27(Kip1) and p21(Cip1) than the alveolar types, explaining, at least in part, the distinct features and outcomes (i.e. a poor prognosis of the alveolar type) of the two forms of this childhood solid cancer. Moreover, the data on butyrate-treated cell lines suggest that the two genes are potential novel therapeutic targets for the treatment of rhabdomyosarcomas.

Structure and gene expression of avian cyclin D2

Avian cyclin D2 (Cyl D2)-encoding cDNA clones were isolated from a chicken UG9 T-cell lambda gt10 library. Sequence analysis revealed a high degree of sequence conservation with both the mouse and human Cyl D2, and somewhat lower similarity with the mouse and human Cyl D1 and D3. The homology is highest between species in the Cyl-box domain which is well conserved among human, mouse and chicken. A single 6.0-kb CYL2 mRNA is produced in both avian B- and T-cells, as expected.

Veterinary drug, 17β-trenbolone promotes the proliferation of human prostate cancer cell line through the Akt/AR signaling pathway

Trenbolone acetate (TBA) is a synthetic anabolic steroidal growth factor that is used for rapid muscle development in cattle. The absorbed TBA is hydrolyzed to the active form, 17β-trenbolone (17 TB; 17β-hydroxy-estra-4,9,11-trien-3-one) in meat and milk products, which can cause adverse health effects in humans. Similar to 5α-dihydrotestosterone (DHT), 17 TB was reported to exhibit endocrine disrupting effects on animals and humans due to its androgenic effect via binding to the androgen receptor. The purpose of this study is to investigate the molecular mechanism of cell proliferation in prostate cancer (PCa) cells treated with 17 TB. We found that 17 TB induces AR-dependent cell proliferation in the human prostate cancer cell line, 22Rv1 in a concentration dependent manner. Treatment with 17 TB increased the expression of cell cycle regulatory proteins, cyclin D2/CDK-4 and cyclin E/CDK-2, whereas the expression of p27 was down-regulated. Furthermore, phosphorylation of Rb and activation of E2F were also induced, which suggests the activation of cyclin D2/CDK-4 and cyclin E/CDK-2 in the cells. When 22Rv1 cells were exposed to 30 pM of 17 TB, which is the effective concentration (EC₅₀) value required to observe proliferative effects on 22Rv1 cells, the expression levels of the phosphorylated forms of Akt and GSK3β were increased. This study demonstrates that 17 TB induces AR-dependent proliferation through the modulation of cell cycle-related proteins in the Akt signaling pathway. The present study provides an effective methodology for identifying cell proliferation signaling of veterinary drugs that exert AR agonistic effects.

v-Abl utilizes multiple mechanisms to drive G1/S progression in fibroblasts

Transformation of 3T3 fibroblasts by the v-Abl tyrosine kinase replaces mitogenic and adhesion signals normally required for cell cycle progression. A 3T3 cell line conditionally transformed with v-Abl has been used to study v-Abl's effects on cell cycle in the context of either serum depletion or absence of adhesion signals. We show that E2F-dependent mRNAs, encoding proteins required for cell cycle progression, are induced by v-Abl. In addition, we identify two previously unknown targets of v-Abl signaling: (1) cyclin D1 and D2 mRNAs are induced upon v-Abl activation; and (2) the CDK inhibitor p27 is decreased upon v-Abl activation.

The expression of pseudogene cyclin D2 mRNA in the human ovary may be a novel marker for decreased ovarian function associated with the aging process

PURPOSE

Our purpose was to investigate the expression pattern of cyclin D2 and pseudogene cyclin D2 mRNA in the human ovary with age.

METHODS

After extraction of the total RNA from ovarian tissues of 23 premenopausal patients, cyclin D2 and pseudogene cyclin D2 mRNAs were measured by the reverse transcription-polymerase chain reaction technique using cyclin D2 and pseudogene cyclin D2 specific primers. Analysis of the cyclin D2 and pseudogene cyclin D2 mRNA expression pattern with age and correlation analysis were carried out.

RESULTS

A 489-bp cyclin D2 band and a 441-bp pseudogene cycin D2 mRNA band were detected in the human ovarian tissue. While cyclin D2 mRNA expression showed a decreasing tendency with age (P = 0.17), pseudogene cyclin D2 mRNA expression increased with age (P < 0.05). Pseudogene cyclin D2 mRNA expression showed a negative correlation with cyclin D2 mRNA (R = -0.35, P < 0.03).

CONCLUSION

The expression of pseudogene cyclin D2 mRNA in the human ovary increases with age, which may be a novel marker for decreased ovarian function associated with the aging process.

Clinical correlation of cyclin D2 mRNA expression in human luteinized granulosa cells

PURPOSE

The aim was to evaluate whether the expression of cyclin D2 mRNA in human luteinized granulosa cells correlates with the clinical parameters of women undergoing in vitro fertilization-embryo transfer (IVF-ET) programs.

METHODS

Using reverse transcriptase-polymerase chain reaction (RT-PCR) techniques, the cyclin D2 mRNA in human luteinized granulosa cells of large follicles was measured. Correlation analysis between cyclin D2 mRNA expression and clinical parameters [age; day 3 follicle-stimulating hormone (FSH), luteinizing hormone (LH), and estradiol (E2); E2 and P4 at the day of human chorionic gonadotropin (hCG); total amount of gonadotropin and the number of days of gonadotropin administration; pregnancy outcome] were performed.

RESULT(S)

Cyclin D2 mRNA expression showed negative correlation with patient's age (R = -0.60, P < 0.005) and total amount of gonadotropins (R = -0.45, P < 0.03), and also showed positive correlation with serum E2 levels at the day of hCG administration (R = 0.55, P < 0.02). Other clinical parameters showed no statistical significance. Cyclin D2 mRNA expression of pregnant group was higher than that of nonpregnant group (P < 0.03).

CONCLUSIONS

Cyclin D2 mRNA expression in human luteinized granulosa cells positively correlates with clinical parameters of ovarian function and may be a novel marker for the health of human ovarian follicle.

The polycomb group gene product Mel-18 interacts with cyclin D2 and modulates its activity

Considerable evidence supports the view that D-type cyclins play a role in G1-S progression. We found that cyclin D2 directly interacts with Mel-18, one of the polycomb group gene products in a yeast two hybrid screen. Further, we have determined the binding domains that are required for interaction between cyclin D2 and Mel-18. The proline/serine-rich domain (P/S domain) of Mel-18 is required to interact with cyclin D2, and the N-terminal region of cyclin D2 is necessary to interact with Mel-18. A co-localization study shows that cyclin D2 and Mel-18 interact within the nucleus. To determine whether Mel-18 affects cyclin D2 activity, we blocked Mel-18 expression using an anti-sense strand system in cyclin D2 over-expressing cells. The results indicate that cells with reduced Mel-18 expression levels show more proliferative activity than the controls. These findings are the first report that Mel-18 directly interacts with cyclin D2 and may inhibit cyclin D2 activity.

HoxD10 gene delivery using adenovirus/adeno-associate hybrid virus inhibits the proliferation and tumorigenicity of GH4 pituitary lactotrope tumor cells

Prolactinoma is one of the most common types of pituitary adenoma. It has been reported that a variety of growth factors and cytokines regulating cell growth and angiogenesis play an important role in the growth of prolactinoma. HoxD10 has been shown to impair endothelial cell migration, block angiogenesis, and maintain a differentiated phenotype of cells. We investigated whether HoxD10 gene delivery could inhibit the growth of prolactinoma. Rat GH4 lactotrope tumor cells were infected with adenovirus/adeno-associated virus (Ad/AAV) hybrid vectors carrying the mouse HoxD10 gene (Hyb-HoxD10) or the beta-galactosidase gene (Hyb-Gal). Hyb-HoxD10 expression inhibited GH4 cell proliferation in vitro. The expression of FGF-2 and cyclin D2 was inhibited in GH4 cells infected with Hyb-HoxD10. GH4 cells transduced with Hyb-HoxD10 did not form tumors in nude mice. These results indicate that the delivery of HoxD10 could potentially inhibit the growth of PRL-secreting tumors. This approach may be a useful tool for targeted therapy of prolactinoma and other neoplasms.

V3 loop of human immunodeficiency virus type 1 reduces cyclin E expression and induces G1 arrest in interleukin 2-dependent T cells

We previously described that V3 loop derived from the HTLV-III BH10 clone V3-BH10 markedly suppressed IL-2-driven T cell proliferation and produced G1 arrest of the cells. Here, we tested the effect of V3-BH10 on the molecules that are involved in transition from the G1 to S phase of the cell cycle. The effect of V3-BH10 on the IL-2-induced expression of G1 cyclins, Cdk inhibitors, and phosphorylation of retinoblastoma protein (pRb) was tested by immunoblotting, using the IL-2-dependent CD4-positive cell line Kit 225. Furthermore, IL-2-dependent kinase activity of the cyclin E-Cdk2 complex was investigated with histone H1 as a substrate. V3-BH10 reduced the IL-2-dependent expression of cyclin E, but not that of cyclin D and Cdk inhibitors such as p21 and p27. As the result of reduction of cyclin E, histone H1 kinase activity of the cyclin E-Cdk2 complex was markedly reduced even in the presence of rIL-2, followed by incomplete phosphorylation of pRb. The reduction in hyperphosphorylation of pRb by V3-BH10 led to G1 arrest of the cell cycle. Thus, V3-BH10 induced G1 arrest in IL-2-dependent cell cycle progression by reducing cyclin E expression, which may be one of the mechanisms underlying the dysfunction of T cells in HIV-1-infected people.

Genomic amplification of CCND2 is rare in non-Hodgkin lymphomas

Cyclin D2, encoded by CCND2 at 12p13, takes part in the regulation of the cell cycle and has been suggested as a candidate for gene amplification in lymphoid malignancies. CCND2 is often overexpressed in chronic B-cell disorders, and we recently detected genomic amplification of the chromosomal region containing CCND2 in two of three investigated non-Hodgkin lymphomas (NHLs) with cytogenetic abnormalities involving 12p. In the present study, 58 NHLs without karyotypic evidence of 12p aberrations were analyzed by fluorescence in situ hybridization with probes for CCND2. No genomic amplification was found, strongly suggesting that this abnormality is rare in such NHLs.

p75NTR enhances PC12 cell tumor growth by a non-receptor mechanism involving downregulation of cyclin D2

p75NTR is a member of the tumor necrosis superfamily of proteins which is variably associated with induction of apoptosis and proliferation. Cyclin D2 is one of the mediators of cellular progression through G1 phase of the cell cycle. The present study demonstrates the inverse relationship between expression of cyclin D2 and expression of p75NTR in PC12 cells. Induction of p75NTR expression in p75NTR-negative PC12 cells results in downregulation of cyclin D2; suppression of p75NTR expression with siRNA in native PC12 cells results in upregulation of cyclin D2. The effects of p75NTR on cyclin D2 expression are mimicked in p75NTR-negative cells by transfection with the intracellular domain of p75NTR. Cyclin-D2-positive PC12 cell cultures grow more slowly than cyclin-D2-negative cultures, and induction of expression of cyclin D2 slows the culture growth rate of cyclin-D2-negative cells. Finally, subcutaneous murine xenografts of cyclin-D2-negative, p75NTR-positive PC12 cells more frequently and more rapidly produce tumors than the analogous xenografts of cyclin-D2-positive, p75NTR-negative cells. These results suggest that p75NTR suppresses cyclin D2 expression in PC12 cells by a mechanism distinct from its function as a nerve growth factor receptor and that cyclin D2 expression decreases cell culture and xenografted tumor growth.

The inhibition of LPS-induced splenocyte proliferation by ortho-substituted and microbially dechlorinated polychlorinated biphenyls is associated with a decreased expression of cyclin D2

Immunological effects of polychlorinated biphenyls (PCBs) have been demonstrated in our laboratories with the peferential inhibition of lipopolysaccharide (LPS)-induced splenocyte proliferation by ortho-substituted PCB congeners. An investigation of the mechanism behind this immunotoxicity revealed an interruption in the progression of murine lymphocytes from G0/G1 into S phase by Aroclor 1242 and the di-ortho-substituted congener, 2,2'-chlorobiphenyl (CB), whereas, a non-ortho-substituted congener, 4,4'-CB, did not affect cell cycle progression. This interruption of cell cycle progression by 2,2'-CB and Aroclor 1242 was associated with a decreased expression of the cell cycle regulatory protein, cyclin D2, while expression was not affected by exposure to the non-ortho-substituted 4,4'-CB. These results suggest the preferential inhibition of LPS-induced splenocyte proliferation by ortho-substituted congeners is a result of a decreased expression of cyclin D2, which leads to an interruption in cell cycle progression. In addition, PCB mixtures with an increased percentage of chlorines in the ortho position following an environmentally occurring degradation process inhibited LPS-induced proliferation, interrupted cell cycle progression, and decreased cyclin D2 expression. This study provides evidence for a mechanism of action of the immunological effects of ortho-substituted individual congeners as well as environmentally relevant mixtures enriched in congeners with this substitution pattern.

LncRNA RNCR3 promotes endothelial cell proliferation and inflammatory cytokine secretion via regulating miR-185-5p/cyclin D2 axis

Endothelial cell is one critical structure of blood vessels, and irregular migration and proliferation of endothelial cell might cause progression of several vascular diseases such as atherosclerosis and restenosis. We showed that TNF-α, PDGF-bb, and IL-1β promote RNCR3 expression in a dose-dependent manner inhuman endothelial cell. RNCR3 level is higher in serum of atherosclerosis patients compared with those in control volunteers. Overexpression of RNCR3 promotes cell proliferation and three inflammatory cytokine secretion including IL-6, IL-1β, and TNF-α in endothelial cell. We illustrated that overexpression of RNCR3 inhibits miR-185-5p expression in endothelial cell. Furthermore, we indicated that miR-185-5p level is lower in the serum of patients with atherosclerosis compared with those in control volunteers. There is a negative correlation between miR-185-5p and RNCR3 expression in serum of patients with atherosclerosis. Using Targetscan, it predicted that miR-185-5p may bind to cyclin D2 and miR-185-5p is one potential target of miR-185-5p. Luciferase reporter data indicated that miR-185-5p suppresses luciferase value of wild-type cyclin D2 while it has no influence of cyclin D2 mutant. Overexpression of RNCR3 enhances cyclin D2 expression in endothelial cell. Moreover, RNCR3 induces cell growth and enhances inflammatory cytokine secretion through modulating cyclin D2 expression in endothelial cell. These results suggested that RNCR3 may serve as one new target for the treatment of atherosclerosis.

D cyclins in CD5+ B-cell lymphoproliferative disorders: cyclin D1 and cyclin D2 identify diagnostic groups and cyclin D1 correlates with ZAP-70 expression in chronic lymphocytic leukemia

We analyzed protein expression of cyclin D1, cyclin D2, and cyclin D3 using high-resolution enzymatic amplification staining and flow cytometry in the neoplastic cells from 80 patients with CD5+ B-cell lymphoproliferative disorders. The D cyclins were expressed differentially in chronic lymphocytic leukemia (CLL), prolymphocytic leukemia (PLL), and mantle cell lymphoma (MCL) with strong staining of cyclin D1 and D2 in MCL, strong staining of cyclin D1 but weak staining of cyclin D2 in 4 of 5 PLLs, and low-level staining for both cyclins in most CLLs. No correlation between cyclin D1 and D2 and growth rates or CD38 expression was observed. However, cyclin D1 levels were significantly higher in ZAP-70+ CLL cases, although no association between ZAP-70 and cyclin D2 was detected. The results indicate that flow cytometric analysis of D cyclins may help in classification of CD5+ B-cell lymphoproliferative disorders.

Low expression of cyclin D2 in G2/M-arrested and transformed proliferating Balb/3T3 cells

At present, the effect of cyclin D2 implicated in cell cycle regulation, differentiation, and oncogenic transformation is not fully confirmed. To better elucidate the role of cyclin D2 in controling the cell proliferation, cyclin D2 expression level was determined at the early initiation and promotion stages during the in vitro two-stage transformation process of Balb/3T3 A31 cells. N-methyl-N'-nitro-N-nitrosoguanidine (MNNG)-induced G2/M-arrested cells expressed low level of cyclin D2 mRNA, while the contact-inhibited nonproliferating cells expressed high level of cyclin D2 mRNA. In the transformed proliferating cells at the promotion stage, cyclin D2 mRNA was not expressed. These data suggest that cyclin D2 expression may be associated with the type of growth arrest and nonproliferating state, but not with the cell proliferation and transformation.

Characterization of cyclin D2 expression in human endometrium

OBJECTIVE

This study was undertaken to investigate cyclin D2 mRNA and protein expression in human endometrium during the menstrual cycle.

METHODS

Endometrial samples were obtained from 15 premenopausal nonpregnant women who had hysterectomies for benign gynecologic reasons. They were divided into the following five groups according to histologic dating: early proliferative (n = 3), mid to late proliferative (n = 3), early secretory (n = 3), mid secretory (n = 3), and late secretory (n = 3). Cyclin D2 mRNA and protein expression were analyzed using reverse transcriptase-polymerase chain reaction, Western blotting, and immunohistochemistry.

RESULTS

Cyclin D2 mRNA and protein were expressed in human endometrial tissue throughout the menstrual cycle. Cyclin D2 mRNA and protein expression of proliferative phase endometrium were significantly higher than those of secretory phase endometrium (P <.05). The staining intensity of cyclin D2 in proliferative phase endometrium was higher than that in secretory phase (P <.05). Cyclin D2 mRNA level showed good correlation with cyclin D2 protein level (R = 0.579, P <.03), and cyclin D2 protein also showed good correlation with immunohistochemical staining intensity (R = 0.562, P <.03).

CONCLUSION

Cyclin D2 was expressed in human endometrium throughout the menstrual cycle. Cyclin D2 mRNA and protein were expressed at high levels in proliferative phase endometrium, especially in the early proliferative phase, and then decreased in the secretory phase.

Cyclin D and cisplatin cytotoxicity in primary neuroblastoma cell lines

Cyclin D1 is a key cell cycle regulator protein with demonstrated oncogenenic activity in a variety of malignancies. Overexpression of Cyclin D1 protein has been observed in many types of tumors. We hypothesized that Cyclin D1 might be an important determinant of the sensitivity of neuroblastomas to cisplatin. Cyclin D1, D2 and D3, and Cdk4, Cdk6 and Rb protein, and Cyclin D1 mRNA expression were measured in primary patient-derived neuroblastoma cell lines. Cell cycle distribution was examined using flow cytometry. A modified MTT assay was used to determine the sensitivity of the cell lines to cisplatin. All 14 cell lines expressed Cyclin D1 protein to a variable extent (0.22-1.47 normalized to actin protein expression). All cell lines expressed Cyclin D2 and D3. There was no relationship between expression of Cyclin D1 and expression of Cyclin D2 or D3 (p>0.05 and R2<0.2 for both). All cell lines expressed Cdk4 and Cdk6 protein. In addition, Rb and two related proteins, p105 and p130, were detected in all the cell lines. The mean cisplatin IC50 was 19.2 microM (range 0.6-40 microM). We conclude that there was no correlation between the amount of Cyclin D1 expressed and the cisplatin IC50. Our results do not support the hypothesis that Cyclin D1 expression is significantly related to cisplatin resistance.