Inadequacies of micronutrient intake in normal weight and overweight young adults aged 18-25 years: a cross-sectional study

OBJECTIVES

This study aims to assess adequacy in micronutrient intake in comparison with reference nutrient intakes (RNI) and to identify differences in intakes between normal weight and overweight individuals.

STUDY DESIGN

A sample of 542 university students (18-25 years), normal weight (N = 369) and overweight (N = 173), were included in a cross-sectional study.

METHODS

A three-day diet diary was used to assess energy and nutrient intake. Body mass index (BMI) and waist circumference were measured.

RESULTS

Mean dietary vitamin D intake was lower than RNI in both men (4.44 μg) and women (5.04 μg). Mean intakes of calcium (597.44 mg), iron (8.62 mg) and folate (171.29 mg) were also lower than recommendations in women. Weight status (normal weight versus overweight) was significantly associated with micronutrient intake, and a trend towards a decrease in vitamin and mineral intake with increasing weight was noted.

CONCLUSIONS

Results suggest the need to increase the intake of some micronutrients to meet the RNI, to ensure optimal health. This study provides a helpful tool to reinforce recommendations and potential health promotion and intervention strategies in university settings and could influence manufacturers involved in new food product development targeted to this young population.

Prostate cancer susceptibility genes: lessons learned and challenges posed

In most developed countries, prostate cancer is the most frequently diagnosed malignancy in men. The extent to which the marked racial/ethnic difference in its incidence rate is attributable to screening methods, environmental, hormonal and/or genetic factors remains unknown. A positive family history is among the strongest epidemiological risk factors for prostate cancer. It is now well recognized that the role of candidate genetic markers to this multifactorial malignancy is more difficult to identify than the identification of other cancer susceptibility genes. Indeed, despite the localization of several susceptibility loci, there has been limited success in identifying high-risk susceptibility genes analogous to BRCA1 or BRCA2 for breast and ovarian cancer. Nonetheless, three strong candidate susceptibility genes have been described, namely ELAC2 (chromosome 17p11/HPC2 region), 2'-5'-oligoadenylate-dependent ribonuclease L (RNASEL), a gene in the HPC1 region, and Macrophage Scavenger Receptor 1 (MSR1), a gene within a region of linkage on chromosome 8p. Additional studies using larger cohorts are needed to fully evaluate the role of these susceptibility genes in prostate cancer risk. It is also of interest to mention that a significant percentage of men with early-onset prostate cancer harbor germline mutation in the BRCA2 gene thus confirming its role as a high-risk prostate cancer susceptibility gene. Although initial segregation analyses supported the hypothesis that a number of rare highly penetrant loci contribute to the Mendelian inheritance of prostate cancer, current experimental evidence better supports the hypothesis that some of the familial risks may be due to inheritance of multiple moderate-risk genetic variants. In this regard, it is not surprising that analyses of genes encoding key proteins involved in androgen biosynthesis and action led to the observation of a significant association between a susceptibility to prostate cancer and common genetic variants in some of those genes.

Hysterectomy: beliefs and attitudes expressed by African-American women

OBJECTIVE

Racial/ethnic differences in the rates of hysterectomy have been noted historically. The aim of this study was to explore the beliefs and attitudes of African-American women regarding hysterectomy recommended for non-life threatening conditions.

METHODS

Women, aged 30-65 years, were recruited from public health clinics and community agencies for participation in focus groups guided by a semi-structured questionnaire. Transcripts were analyzed both manually and using NUD*IST software.

RESULTS

Thirty-eight women participated in six focus groups. Hysterectomy had been recommended for 15% of the women. Four categories and 11 themes emerged from the sessions. Categories included: definitions of hysterectomy and medical indications; resources consulted in the decision-making process; outcomes of hysterectomy; and interactions with the health care community.

CONCLUSION

It is important to assess a patient's perceptions and preferences regarding treatment options. The women in this study advocated the delay or avoidance of surgery, or the use of alternative methods of treatment in lieu of hysterectomy for non-cancerous conditions. Physicians who recommend hysterectomy should consider the attitudes, beliefs, and knowledge of patients.

Emotional impact of retirement on physicians

The current study sought to identify the factors underlying physicians' decision to retire, describe the emotional impact of retirement on physicians, measure quality of life in retirement, and identify coping strategies used by retired physicians. A questionnaire was sent to all 689 retired members of the Harris County Medical Society, and 323 (47%) responded. Data were analyzed using SPSS. Physicians overwhelmingly indicated positive reasons for retirement, although one third said that loss of autonomy and control in medical practice were factors. Participants were satisfied with retirement and enjoyed low levels of stress and depression. Spousal and personal health had the largest negative impact on retirement. Being prepared emotionally significantly affected physicians' attitudes. Longitudinal studies and research on the impact of managed care on the retirement experience are needed. Younger physicians need to be prepared for the emotional impact of retirement.

Identification of an overlapping binding domain on Cdc20 for Mad2 and anaphase-promoting complex: model for spindle checkpoint regulation

Activation of the anaphase-promoting complex (APC) is required for anaphase initiation and for exit from mitosis in mammalian cells. Cdc20, which specifically recognizes APC substrates involved in the metaphase-to-anaphase transition, plays a pivotal role in APC activation through direct interaction with the APC. The activation of the APC by Cdc20 is prevented by the interaction of Cdc20 with Mad2 when the spindle checkpoint is activated. Using deletion mutagenesis and peptide mapping, we have identified the sequences in Cdc20 that target it to Mad2 and the APC, respectively. These sequences are distinct but overlapping, providing a possible structural explanation for the internal modulation of the APC-Cdc20 complex by Mad2. In the course of these studies, a truncation mutant of Cdc20 (1-153) that constitutively binds Mad2 but fails to bind the APC was identified. Overexpression of this mutant induces the formation of multinucleated cells and increases their susceptibility to undergoing apoptosis when treated with microtubule-inhibiting drugs. Our experiments demonstrate that disruption of the Mad2-Cdc20 interaction perturbs the mitotic checkpoint, leading to premature activation of the APC, sensitizing the cells to the cytotoxic effects of microtubule-inhibiting drugs.

Three RNA polymerase II carboxyl-terminal domain kinases display distinct substrate preferences

CDK7, CDK8, and CDK9 are cyclin-dependent kinases (CDKs) that phosphorylate the C-terminal domain (CTD) of RNA polymerase II. They have distinct functions in transcription. Because the three CDKs target only serine 5 in the heptad repeat of model CTD substrates containing various numbers of repeats, we tested the hypothesis that the kinases differ in their ability to phosphorylate CTD heptad arrays. Our data show that the kinases display different preferences for phosphorylating individual heptads in a synthetic CTD substrate containing three heptamer repeats and specific regions of the CTD in glutathione S-transferase fusion proteins. They also exhibit differences in their ability to phosphorylate a synthetic CTD peptide that contains Ser-2-PO(4). This phosphorylated peptide is a poor substrate for CDK9 complexes. CDK8 and CDK9 complexes, bound to viral activators E1A and Tat, respectively, target only serine 5 for phosphorylation in the CTD peptides, and binding to the viral activators does not change the substrate preference of these kinases. These results imply that the display of different CTD heptads during transcription, as well as their phosphorylation state, can affect their phosphorylation by the different transcription-associated CDKs.

BRG1, a component of the SWI-SNF complex, is mutated in multiple human tumor cell lines

Human BRG1 is a component of the evolutionarily conserved SWI-SNF chromatin remodeling complex. BRG1 has been implicated in growth control through its interaction with the tumor suppressor pRb and may consequently serve as a negative regulator of proliferation. Postulating that BRG1 may itself be a tumor suppressor gene, we screened a panel of tumor cell lines to determine whether the gene is targeted for mutation. We report that the COOH-terminal region of BRG1 is homozygously deleted in two carcinoma cell lines, prostate TSU-Pr1 and lung A-427. In addition, biallelic inactivations of BRG1 were observed in four other cell lines derived from carcinomas of the breast, lung, pancreas, and prostate; their mutations in BRG1 included three frameshift lesions and one nonsense lesion. Point mutations were also discovered in a number of other cell lines, however in most cases any effect of these mutations on BRG1 function remains to be established. A variety of different mutations within BRG1, in several cell lines, suggest that BRG1 may be targeted for disruption in human tumors. Significantly, reintroduction of BRG1 into cells lacking BRG1 expression was sufficient to reverse their transformed phenotype inducing growth arrest and a flattened morphology. These data strongly support the model that BRG1 may function as a tumor suppressor and strengthen the hypothesis that the regulation of gene expression through chromatin remodeling is critical for cancer progression. It will be important to confirm these observations in primary tumors.

The mitotic serine/threonine kinase Aurora2/AIK is regulated by phosphorylation and degradation

Aurora2 is a cell cycle regulated serine/threonine protein kinase which is overexpressed in many tumor cell lines. We demonstrate that Aurora2 is regulated by phosphorylation in a cell cycle dependent manner. This phosphorylation occurs on a conserved residue, Threonine 288, within the activation loop of the catalytic domain of the kinase and results in a significant increase in the enzymatic activity. Threonine 288 resides within a consensus motif for the cAMP dependent kinase and can be phosphorylated by PKA in vitro. The protein phosphatase 1 is shown to dephosphorylate this site in vitro, and in vivo the phosphorylation of T288 is induced by okadaic acid treatment. Furthermore, we show that the Aurora2 kinase is regulated by proteasome dependent degradation and that Aurora2 phosphorylated on T288 may be targeted for degradation during mitosis. Our experiments suggest that phosphorylation of T288 is important for regulation of the Aurora2 kinase both for its activity and its stability.

Stat3-dependent induction of p19INK4D by IL-10 contributes to inhibition of macrophage proliferation

We have previously reported that IL-10 inhibits proliferation of normal bone marrow-derived macrophages and of the monocyte/macrophage cell line J774. Activation of Stat3 was shown to be necessary and sufficient to mediate inhibition of proliferation. To investigate further the mechanism of growth arrest, we examined the effect of IL-10 on expression of cell cycle inhibitors. We found that IL-10 treatment increases expression of the cyclin-dependent kinase inhibitors p19INK4D and p21CIP1 in macrophages. IL-10 cannot induce p19INK4D expression or block proliferation when Stat3 signaling is blocked by a dominant negative Stat3 or a mutant IL-10Ralpha which does not recruit Stat3 in J774 cells, whereas p21CIP1 induction is not affected. An inducibly active Stat3 (coumermycin-dimerizable Stat3-Gyrase B), which suppresses J774 cell proliferation, also induced p19INK4D expression. Sequencing of the murine p19INK4D promoter revealed two candidate Stat3 binding sites, and IL-10 treatment activated a reporter gene controlled by this promoter. These data suggest that Stat3-dependent induction of p19INK4D mediates inhibition of proliferation. Enforced expression of murine p19INK4D cDNA J774 cells significantly reduced their proliferation. Use of antisense p19INK4D and analysis of p19INK4D-deficient macrophages confirmed that p19INK4D is required for optimal inhibition of proliferation by IL-10, and indicated that additional IL-10 signaling events contribute to this response. These data indicate that Stat3-dependent induction of p19INK4D and Stat3-independent induction of p21CIP1 are important components of the mechanism by which IL-10 blocks proliferation in macrophages.

Cyclin D2 is essential for BCR-mediated proliferation and CD5 B cell development

Progression into G(1) in B lymphocytes is regulated by cyclins D2 and D3, components of the cell cycle machinery currently believed to have overlapping and potentially redundant roles in cell cycle control. To study the specific role of cyclin D2 in B lymphocyte proliferation, we examined B cells from cyclin D2(-/-) mice and demonstrate a specific requirement for cyclin D2 in BCR- but not CD40- or lipopolysaccharide-induced proliferation. Furthermore, conventional B cell development proceeds normally in the mutant mice; however, the CD5 B cell compartment is dramatically reduced, suggesting that cyclin D2 is important in CD5 B cell development as well as antigen-dependent B cell clonal expansion.

Decision making, beliefs, and attitudes toward hysterectomy: a focus group study with medically underserved women in Texas

Variations in hysterectomy rates have been associated with assorted physician and patient characteristics, and the disproportionate rate of hysterectomies in African American women has been attributed to a higher prevalence of leiomyomas. The role of women's beliefs and attitudes toward hysterectomy and participation in decision making for medical treatment has not been explored as a source of variance. The purposes of this qualitative study were to explore these constructs in a triethnic sample of women to understand beliefs, attitudes, and decision-making preferences among underserved women; to facilitate development of a quantitative survey; and to inform development of interventions to assist women with such medical decisions. Twenty-three focus groups were conducted with 148 women from community sites and public health clinics. Thirteen self-identified lesbians participated in three groups. Analysis of audiotaped transcripts yielded four main themes: perceived outcomes of hysterectomy, perceived views of men/partners, opinions about healthcare providers, decision-making process. Across groups, the women expressed similar expectations from hysterectomy, differing only in the degree to which dimensions were emphasized. The women thought men perceived women with hysterectomy as less desirable for reasons unrelated to childbearing. Attitudes toward physicians were negative except among Hispanic women. All women expressed a strong desire to be involved in elective treatment decisions and would discuss their choice with important others. Implications for intervention development include enhancing women's skills and confidence to evaluate treatment options and to interact with physicians around treatment choices and creation of portable educational components for important others.

A novel growth- and cell cycle-regulated protein, ASK, activates human Cdc7-related kinase and is essential for G1/S transition in mammalian cells

A novel human protein, ASK (activator of S phase kinase), was identified on the basis of its ability to bind to human Cdc7-related kinase (huCdc7). ASK forms an active kinase complex with huCdc7 that is capable of phosphorylating MCM2 protein. ASK appears to be the major activator of huCdc7, since immunodepletion of ASK protein from the extract is accompanied by the loss of huCdc7-dependent kinase activity. Expression of ASK is regulated by growth factor stimulation, and levels oscillate through the cell cycle, reaching a peak during S phase. Concomitantly, the huCdc7-dependent kinase activity significantly increases when cells are in S phase. Furthermore, we have demonstrated that ASK serves an essential function for entry into S phase by showing that microinjection of ASK-specific antibodies into mammalian cells inhibited DNA replication. Our data show that ASK is a novel cyclin-like regulatory subunit of the huCdc7 kinase complex and that it plays a pivotal role in G1/S transition in mammalian cells.

Mammalian Srb/Mediator complex is targeted by adenovirus E1A protein

Adenovirus E1A proteins prepare the host cell for viral replication, stimulating cell cycling and viral transcription through interactions with critical cellular regulatory proteins such as RB and CBP. Here we show that the E1A zinc-finger domain that is required to activate transcription of viral early genes binds to a host-cell multiprotein complex containing homologues of yeast Srb/Mediator proteins. This occurs through a stable interaction with the human homologue of Caenorhabditis elegans SUR-2, a protein required for many developmental processes in the nematode. This human Srb/Mediator complex stimulates transcription in vitro in response to both the E1A zinc-finger and the herpes simplex virus VP16 activation domains. Interaction with human Sur-2 is also required for transcription to be activated by the activation domain of a transcription factor of the ETS-family in response to activated mitogen-activated protein (MAP) kinase.

Cyclin D-CDK subunit arrangement is dependent on the availability of competing INK4 and p21 class inhibitors

The D-type cyclins and their major kinase partners CDK4 and CDK6 regulate G0-G1-S progression by contributing to the phosphorylation and inactivation of the retinoblastoma gene product, pRB. Assembly of active cyclin D-CDK complexes in response to mitogenic signals is negatively regulated by INK4 family members. Here we show that although all four INK4 proteins associate with CDK4 and CDK6 in vitro, only p16(INK4a) can form stable, binary complexes with both CDK4 and CDK6 in proliferating cells. The other INK4 family members form stable complexes with CDK6 but associate only transiently with CDK4. Conversely, CDK4 stably associates with both p21(CIP1) and p27(KIP1) in cyclin-containing complexes, suggesting that CDK4 is in equilibrium between INK4 and p21(CIP1)- or p27(KIP1)-bound states. In agreement with this hypothesis, overexpression of p21(CIP1) in 293 cells, where CDK4 is bound to p16(INK4a), stimulates the formation of ternary cyclin D-CDK4-p21(CIP1) complexes. These data suggest that members of the p21 family of proteins promote the association of D-type cyclins with CDKs by counteracting the effects of INK4 molecules.

Cyclin E associates with BAF155 and BRG1, components of the mammalian SWI-SNF complex, and alters the ability of BRG1 to induce growth arrest

SWI-SNF complexes have been implicated in transcriptional regulation by chromatin remodeling. We have identified an interaction between two components of the mammalian SWI-SNF complex and cyclin E, an essential cell cycle regulatory protein required for G1/S transition. BRG1 and BAF155, mammalian homologs of yeast SWI2 and SWI3, respectively, are found in cyclin E complexes and are phosphorylated by cyclin E-associated kinase activity. In this report, we show that overexpression of BRG1 causes growth arrest and induction of senescence-associated beta-galactosidase activity, which can be overcome by cyclin E. Our results suggest that cyclin E may modulate the activity of the SWI-SNF apparatus to maintain the chromatin in a transcriptionally permissive state.

Cyclin C/CDK8 and cyclin H/CDK7/p36 are biochemically distinct CTD kinases

Phosphorylation of the carboxyl-terminal domain (CTD) of RNA polymerase II is important for basal transcriptional processes in vivo and for cell viability. Several kinases, including certain cyclin-dependent kinases, can phosphorylate this substrate in vitro. It has been proposed that differential CTD phosphorylation by different kinases may regulate distinct transcriptional processes. We have found that two of these kinases, cyclin C/CDK8 and cyclin H/CDK7/p36, can specifically phosphorylate distinct residues in recombinant CTD substrates. This difference in specificity may be largely due to their varying ability to phosphorylate lysine-substituted heptapeptide repeats within the CTD, since they phosphorylate the same residue in CTD consensus heptapeptide repeats. Furthermore, this substrate specificity is reflected in vivo where cyclin C/ CDK8 and cyclin H/CDK7/p36 can differentially phosphorylate an endogenous RNA polymerase II substrate. Several small-molecule kinase inhibitors have different specificities for these related kinases, indicating that these enzymes have diverse active-site conformations. These results suggest that cyclin C/CDK8 and cyclin H/CDK7/p36 are physically distinct enzymes that may have unique roles in transcriptional regulation mediated by their phosphorylation of specific sites on RNA polymerase II.

A human RNA polymerase II complex containing factors that modify chromatin structure

We have isolated a human RNA polymerase II complex that contains chromatin structure remodeling activity and histone acetyltransferase activity. This complex contains the Srb proteins, the Swi-Snf complex, and the histone acetyltransferases CBP and PCAF in addition to RNA polymerase II. Notably, the general transcription factors are absent from this complex. The complex was purified by two different methods: conventional chromatography and affinity chromatography using antibodies directed against CDK8, the human homolog of the yeast Srb10 protein. Protein interaction studies demonstrate a direct interaction between RNA polymerase II and the histone acetyltransferases p300 and PCAF. Importantly, p300 interacts specifically with the nonphosphorylated, initiation-competent form of RNA polymerase II. In contrast, PCAF interacts with the elongation-competent, phosphorylated form of RNA polymerase II.

NAT, a human complex containing Srb polypeptides that functions as a negative regulator of activated transcription

A complex that represses activated transcription and contains the human homologs of the yeast Srb7, Srb10, Srb11, Rgr1, and Med6 proteins was isolated. The complex is devoid of the Srb polypeptides previously shown to be components of the yeast Mediator complex that functions in transcriptional activation. The complex phosphorylates the CTD of RNA polymerase II (RNAPII) at residues other than those phosphorylated by the kinase of TFIIH. Moreover, the complex specifically interacts with RNAPII. The interaction is not mediated by the CTD of RNAPII, but is precluded by phosphorylation of the CTD. Our results indicate that the complex is a subcomplex of the human RNAPII holoenzyme. We suggest that the RNAPII holoenzyme is a transcriptional control panel, integrating and responding to specific signals to activate or repress transcription.

Cyclin E associates with components of the pre-mRNA splicing machinery in mammalian cells

Cyclin E-cdk2 is a critical regulator of cell cycle progression from G1 into S phase in mammalian cells. Despite this important function little is known about the downstream targets of this cyclin-kinase complex. Here we have identified components of the pre-mRNA processing machinery as potential targets of cyclin E-cdk2. Cyclin E-specific antibodies coprecipitated a number of cyclin E-associated proteins from cell lysates, among which are the spliceosome-associated proteins, SAP 114, SAP 145, and SAP 155, as well as the snRNP core proteins B' and B. The three SAPs are all subunits of the essential splicing factor SF3, a component of U2 snRNP. Cyclin E antibodies also specifically immunoprecipitated U2 snRNA and the spliceosome from splicing extracts. We demonstrate that SAP 155 serves as a substrate for cyclin E-cdk2 in vitro and that its phosphorylation in the cyclin E complex can be inhibited by the cdk-specific inhibitor p21. SAP 155 contains numerous cdk consensus phosphorylation sites in its N terminus and is phosphorylated prior to catalytic step II of the splicing pathway, suggesting a potential role for cdk regulation. These findings provide evidence that pre-mRNA splicing may be linked to the cell cycle machinery in mammalian cells.

Phosphorylation of spliceosomal protein SAP 155 coupled with splicing catalysis

The U2 snRNP component SAP 155 contacts pre-mRNA on both sides of the branch site early in spliceosome assembly and is therefore positioned near or at the spliceosome catalytic center. We have isolated a cDNA encoding human SAP 155 and identified its highly related Saccharomyces cerevisiae homolog (50% identity). The carboxy-terminal two-thirds of SAP 155 shows the highest conservation and is remarkably similar to the regulatory subunit A of the phosphatase PP2A. Significantly, SAP 155 is phosphorylated concomitant with or just after catalytic step one, making this the first example of a protein modification tightly regulated with splicing catalysis.

Transgene expression of bcl-xL permits anti-immunoglobulin (Ig)-induced proliferation in xid B cells

Mutations in the tyrosine kinase, Btk, result in a mild immunodeficiency in mice (xid). While B lymphocytes from xid mice do not proliferate to anti-immunoglobulin (Ig), we show here induction of the complete complement of cell cycle regulatory molecules, though the level of induction is about half that detected in normal B cells. Cell cycle analysis reveals that anti-Ig stimulated xid B cells enter S phase, but fail to complete the cell cycle, exhibiting a high rate of apoptosis. This correlated with a decreased ability to induce the anti-apoptosis regulatory protein, Bcl-xL. Ectopic expression of Bcl-xL in xid B cells permitted anti-Ig induced cell cycle progression demonstrating dual requirements for induction of anti-apoptotic proteins plus cell cycle regulatory proteins during antigen receptor mediated proliferation. Furthermore, our results link one of the immunodeficient traits caused by mutant Btk with the failure to properly regulate Bcl-xL.

Active cdk6 complexes are predominantly nuclear and represent only a minority of the cdk6 in T cells

We have performed biochemical analyses of cdk6 complexes in T cells. By gel filtration chromatography we observed at least three cdk6 containing complexes in the cell, the most abundant eluting at 450 kDa and 50-70 kDa and a minor complex eluting at 170 kDa. Cyclin D was present in the minor 170 kDa complex which co-eluted with the peak of cdk associated in vitro Rb kinase activity. Analysis of proteins that co-immunoprecipitated with cdk6 showed that the 450 kDa complex contained both Hsp90 and CDC37. The 50-70 kDa complex was made up of two moieties, a 66 kDa complex containing cdk6 bound to p19INK4d and monomeric cdk6. The subcellular localisation of the cdk6 complexes was analysed by preparing cytoplasmic and nuclear extracts. The 450 kDa complex was shown to be predominantly cytoplasmic, whereas the 170 kDa cyclin D/cdk6 and the 50-70 kDa complexes were present in both nuclear and cytoplasmic compartments. When these same extracts were assayed for cdk6 associated kinase activity, only the nuclear cdk6 complexes were active. These data suggest that even though there are cdk6/cyclin D complexes detectable in both the cytoplasm and nucleus, only the cdk6 that is in the nucleus is active.

Raf-induced proliferation or cell cycle arrest is determined by the level of Raf activity with arrest mediated by p21Cip1

The Raf family of protein kinases display differences in their abilities to promote the entry of quiescent NIH 3T3 cells into the S phase of the cell cycle. Although conditional activation of deltaA-Raf:ER promoted cell cycle progression, activation of deltaRaf-1:ER and deltaB-Raf:ER elicited a G1 arrest that was not overcome by exogenously added growth factors. Activation of all three deltaRaf:ER kinases led to elevated expression of cyclin D1 and cyclin E and reduced expression of p27Kip1. However, activation of deltaB-Raf:ER and deltaRaf-1:ER induced the expression of p21Cip1, whereas activation of deltaA-Raf:ER did not. A catalytically potentiated form of deltaA-Raf:ER, generated by point mutation, strongly induced p21Cip1 expression and elicited cell cycle arrest similarly to deltaB-Raf:ER and deltaRaf-1:ER. These data suggested that the strength and duration of signaling by Raf kinases might influence the biological outcome of activation of this pathway. By titration of deltaB-Raf:ER activity we demonstrated that low levels of Raf activity led to activation of cyclin D1-cdk4 and cyclin E-cdk2 complexes and to cell cycle progression whereas higher Raf activity elicited cell cycle arrest correlating with p21Cip1 induction and inhibition of cyclin-cdk activity. Using green fluorescent protein-tagged forms of deltaRaf-1:ER in primary mouse embryo fibroblasts (MEFs) we demonstrated that p21Cip1 was induced by Raf in a p53-independent manner, leading to cell cycle arrest. By contrast, activation of Raf in p21Cip1(-/-) MEFs led to a robust mitogenic response that was similar to that observed in response to platelet-derived growth factor. These data indicate that, depending on the level of kinase activity, Raf can elicit either cell cycle progression or cell cycle arrest in mouse fibroblasts. The ability of Raf to elicit cell cycle arrest is strongly associated with its ability to induce the expression of the cyclin-dependent kinase inhibitor p21Cip1 in a manner that bears analogy to alpha-factor arrest in Saccharomyces cerevisiae. These data are consistent with a role for Raf kinases in both proliferation and differentiation of mammalian cells.

Breast carcinomas occurring in young women (< 35 years) are different

One hundred and sixty-three breast carcinomas occurring in women aged between 26 and 44 years were examined for pathological features, oestrogen and progesterone receptor status, proliferation as determined by Ki-67 labelling and the presence of c-erbB-2 and p53 protein, and were compared with a control group of carcinomas from women in the 50-67 years age group. Carcinomas occurring in women aged under 35 years had a significantly high incidence of being poorly differentiated and of having high proliferation rates. This group also had a significantly high incidence of p53 protein staining. Carcinomas in the under 30 years age group had a lower incidence of oestrogen and progesterone receptor positivity. No differences were found in c-erbB-2-positive staining between the groups. Infiltrating lobular carcinomas were only identified in women aged 40 years and over. There was a higher incidence of a family history in the 35-44 years age group (18%) than in the under 35 years age group (11%). Breast carcinomas occurring in women aged under 35 years are more aggressive. An important finding is the high incidence of p53 positivity, which may indicate genetic instability.

Induction of cell cycle regulatory proteins in anti-immunoglobulin-stimulated mature B lymphocytes

Progression through the cell cycle is a tightly controlled process that integrates signals generated at the plasma membrane with the proteins that form the cell cycle machinery. The current study chronicles the induction of cyclins, cyclin-dependent kinases (cdk), and cdk inhibitors in low density primary mouse B lymphocytes after anti-immunoglobulin plus interleukin 4 (IgM + IL-4) stimulation. In this system, > 85% of cells remain in the G0/G1 phase of cell cycle for an initial 24-h period, followed by entry of up to 50% of the cells into S phase, commencing around 30 h and peaking at 48 h. Extensive time course analyses of these anti-IgM + IL-4-stimulated B cells revealed that the G1-associated D-type cyclins D2 and D3 were induced by 3 h after stimulation, and that cyclins E, A, and B were subsequently induced sequentially, beginning at mid-G1, G1/S transition, and S phase, respectively. The G1-associated cyclin D1 was not expressed at any stage of the anti-Ig + IL-4-induced B cell cycle. cdk2, cdk4, and cdk6 were induced during G1, whereas cell division cycle-2 (cdc2) was induced concomitantly with S phase. Irrespective of their expression, the kinases cdk2 and cdc2 were only active from S phase onwards, suggesting that productive cyclin/kinase complex formation did not occur until that time. Cell cycle inhibitors p21 and p19 were induced by anti-Ig + IL-4, peaking in expression at mid-G1 and S phase, respectively. Stimulation of low density B cells with anti-Ig + IL-4 caused rapid down regulation of the p27 inhibitor, however this protein was reexpressed at 54-96 h after stimulation. In contrast, B cells stimulated with anti-CD40, a stimulus which induces long-term B cell proliferation, permanently down regulated p27. These findings are consistent with the concept that p27 reexpression contributes to the G1 arrest that follows antigen receptor crosslinking. Low density B cells cultured in the viability-enhancing cytokine IL-4 alone also showed induction of D2 and D3 cyclin expression. However, the D2 expression was transient, and the D3 expression was substantially lower than that observed in B cells induced to proliferate by anti-Ig + IL-4. This partial induction of D2 and D3 expression may explain IL-4's ability to promote B cell entry into G1 but not S phase of cell cycle, and furthermore, its ability to truncate G1 progression when B cells are subsequently stimulated with anti-Ig.

Cyclin C/CDK8 is a novel CTD kinase associated with RNA polymerase II

A number of cyclin/kinase complexes have been identified in mammalian cells that are essential for controlled cell proliferation. Cyclin C was isolated by virtue of its ability to rescue the triple CLN mutation in yeast; however, until now its function has remained unclear. Cyclin C associates with a novel cyclin dependent kinase, CDK8, and we demonstrate that this complex is associated with kinase activity towards the carboxy-terminal domain (CTD) of RNA polymerase II. We have identified at least two distinct cyclin C/CDK8 containing complexes within the cell, a larger complex over 500 kD in size, that also contains the largest subunit of RNA polymerase II, and a smaller 170 kD species. Both of these cyclin C complexes retain potent CTD kinase activity. We further demonstrate that the cyclin C/CDK8 complex associates with the large subunit of RNA polymerase II in vivo, implicating a potential role for cyclin C/CDK8 in regulating its activities.

A human RNA polymerase II complex associated with SRB and DNA-repair proteins

We report here the isolation of a human RNA polymerase II complex containing a subset of the basal transcription factors and the human homologues of the yeast SRB (for suppressors of RNA polymerase B) proteins. The complex contains transcriptional coactivators and increases the activation of transcription. In addition, some components of the RNA polymerase II complex participate in DNA repair.

Cyclin dependent kinase regulation

Cyclin-dependent kinases (CDKs) are key regulators of the cell cycle and their activities are consequently tightly regulated. Recent developments in the field of CDK regulation have included the discovery and characterization of CDK inhibitors. These developments have had an impact on our understanding of how other signalling pathways may be linked to the cell cycle machinery.

Cyclin D3 is essential for megakaryocytopoiesis

A normal cell cycle in most eukaryotic cells consists of a tightly regulated sequence of phases including DNA synthesis (S) followed by a gap (G2), mitosis (M), and a gap (G1). In the megakaryocytic lineage, the cells undergo endomitosis, which involves DNA synthesis in the absence of mitosis, thus giving rise to polyploid cells. We aimed at defining whether the megakaryocytic cell cycle consists of a continuous S phase or of G1/S phases and at determining which cyclins are involved in this process. Studies were performed in primary cultures of mouse bone marrow cells. DNA synthesis in megakaryocytes was followed by determining incorporation of a DNA precursor, bromodeoxyuridine (BrdU), into the cells by in situ staining for BrdU. These experiments showed that no more than 15% of the recognizable megakaryocytes in normal bone marrow are in the process of endomitosis, including S phases interrupted by short gaps. Using immunohistochemistry, we showed that mature megakaryocytes express the G1 phase cyclin and cyclin D3, but not the mitotic cyclin, cyclin B1. Under culture conditions that selectively promote megakaryocytopoiesis, antisense oligonucleotides designed to suppress cyclin D3 expression, but not sense oligonucleotides or antisense oligonucleotides to cyclin B1, dramatically suppress endomitosis and abrogate megakaryocyte development. Our results indicate that endoreduplication in megakaryocytes is associated with low levels of or the absence of cyclin B1, whereas progression through this process depends on the G1 phase for which cyclin D3 is crucial.

Mammary hyperplasia and carcinoma in MMTV-cyclin D1 transgenic mice

Physical associations between cyclins, viral oncogenes and tumour suppressor genes imply a central role for cyclins in growth control. Cyclin D1 was identified as a candidate oncogene (PRAD1) in tumour-specific DNA rearrangements and is suspected to be a contributor to several types of neoplasms including breast cancer. Cyclin D1 also rescues G1 cyclin-defective Saccharomyces cerevisiae, and is a growth-regulated gene. Despite evidence suggesting that cyclin D1 is an oncogene, its ability to transform cells directly in culture remains controversial. To evaluate its potential to deregulate growth in vivo in a physiologically relevant tissue we overexpressed cyclin D1 in mammary cells in transgenic mice. We report here that overexpression of cyclin D1 resulted in abnormal mammary cell proliferation including the development of mammary adenocarcinomas. We conclude that overexpression of cyclin D1 deregulates cell proliferation and can induce tumorigenic changes in mammary tissues, suggesting that cyclin D1 indeed plays an important oncogenic role in breast cancer.

A cell cycle-regulated inhibitor of cyclin-dependent kinases

Cyclin-dependent kinases (Cdks) previously have been shown to drive the major cell cycle transitions in eukaryotic organisms ranging from yeast to humans. We report here the identification of a 28-kDa protein, p28Ick (inhibitor of cyclin-dependent kinase), that binds to and inhibits the kinase activity of preformed Cdk/cyclin complexes from human cells. p28 inhibitory activity fluctuates during the cell cycle with maximal levels in G1 and accumulates in G1- and G0-arrested cells. These results suggest that control of the G1/S transition may be influenced by a family of Cdk inhibitors that include p28Ick and the recently described inhibitors p21Cip1/Waf1/Cap20 and p16Ink4.

Modulation of cyclin gene expression by adenovirus E1A in a cell line with E1A-dependent conditional proliferation

To investigate how adenovirus E1A controls cell proliferation, we have fused E1A to the hormone-binding domain of the human estrogen receptor (ER) and introduced the E1A-ER chimeric gene together with an activated ras gene into primary rat embryo fibroblasts. Cell lines derived from this transfection proliferate in an estrogen-dependent manner. Estrogen-dependent activation of E1A-ER led to a rapid induction of both cyclin E and cyclin A gene expression. In contrast, levels of cyclin D1 were strongly reduced by activation of E1A-ER. Similar changes in cyclin gene expression were observed when primary human fibroblasts were infected with wild-type adenovirus and when adenovirus E1A was stably expressed in NIH 3T3 cells. Our findings suggest that activation of cyclin A and E, but not D1, gene expression by E1A precedes and may be responsible for E1A-dependent cell proliferation. In contrast, we found that quantitative disruption of complexes between the E2F transcription factor and the retinoblastoma protein is not required for E1A-dependent S-phase entry.

p53-dependent inhibition of cyclin-dependent kinase activities in human fibroblasts during radiation-induced G1 arrest

gamma-Irradiation of human diploid fibroblasts in the G1 interval caused arrest of the cell cycle prior to S phase. This cell cycle block was correlated with a lack of activation of both cyclin E-Cyclin-dependent kinase 2 (Cdk2) and cyclin A-Cdk2 kinases and depended on wild-type p53. Although the accumulation of cyclin A was strongly inhibited in gamma-irradiated cells, cyclin E accumulated and bound Cdk2 at normal levels but remained in an inactive state. We found that both whole-cell lysates and inactive cyclin E-Cdk2 complexes prepared from irradiated cells contained an activity capable of inactivating cyclin E-Cdk2 complexes. The protein responsible for this activity was shown to be p21CIP1/WAF1, recently described as a p53-inducible Cdk inhibitor. Our data suggest a model in which ionizing radiation confers G1 arrest via the p53-mediated induction of a Cdk inhibitor protein.

Cyclin E, a potential prognostic marker for breast cancer

A fundamental cause of cancer is changed properties of genetic material, which may deregulate normal development of the tissue or provide selective growth advantage to the tumor cell. This deregulation of cell proliferation results from altered production of a handful of proteins that play key roles in progression through the eukaryotic cell cycle. Some of these proteins include tumor suppressor genes or oncogenes. However, no one general change or alteration of a critical gene has yet been found in all cancers. Using surgical material obtained from patients with various malignancies, we show that breast cancers and other solid tumors, as well as malignant lymphocytes from patients with lymphatic leukemia, show severe quantitative and qualitative alterations in cyclin E protein production independent of the S-phase fraction of the samples. Hence, these alterations represent a true difference between normal versus tumor tissue. In addition, in breast cancer, the alterations in cyclin E expression become progressively worse with increasing stage and grade of the tumor, suggesting its potential use as a new prognostic marker.

Altered regulation of G1 cyclins in senescent human diploid fibroblasts: accumulation of inactive cyclin E-Cdk2 and cyclin D1-Cdk2 complexes

Senescent human diploid fibroblasts are unable to enter S phase in response to mitogenic stimulation. One of the key deficiencies in mitogen-stimulated senescent cells is their failure to phosphorylate the retinoblastoma protein, which acts as an inhibitor of entry into S phase in its unphosphorylated form. Recent data suggest that cyclin-dependent kinases (Cdks) regulated by G1 cyclins (D type and E) are responsible for the primary phosphorylation of the retinoblastoma protein prior to the G1/S boundary. Surprisingly, we found 10- to 15-fold higher constitutive amounts of both cyclin E and cyclin D1 in senescent cells compared to quiescent early-passage cells. Nevertheless, cyclin E-associated kinase activity in senescent cells was very low and did not increase significantly upon mitogenic stimulation even though cyclin E-Cdk2 complexes were abundant. In contrast to early-passage cells in late G1 phase, senescent cells contained mainly underphosphorylated cyclin E and proportionally more unphosphorylated and inactive Cdk2, perhaps accounting for the low kinase activity. We also show that a majority of the Cdk2 in senescent cells, but not in early-passage cells, was complexed with cyclin D1. Cyclin D1-Cdk2 complexes, severalfold enriched in senescent cells, contained exclusively unphosphorylated Cdk2. Amounts of cyclin A, which ordinarily accumulates in S and G2 phases, were extremely low in stimulated senescent cells. We suggest that the failure to activate cyclin E-Cdk2 kinase activity in senescent cells may account for the inability of these cells to phosphorylate the retinoblastoma protein in late G1 phase, which in turn may block the expression of late G1 genes such as cyclin A that are required for entry into S phase.

The cdk2 kinase is required for the G1-to-S transition in mammalian cells

In the cell cycle of fission and budding yeast, the p34cdc2/CDC28 kinase is required for both the G1-to-S and G2-to-M phase transitions. In vertebrates, the homologous p34cdc2 kinase is required for G2-to-M phase transitions but appears to be dispensable for DNA synthesis. We have investigated the function of a related kinase, p33cdk2, using serum-stimulated quiescent human fibroblasts. While the p33cdk2 protein was expressed at constant levels throughout the cell cycle, p33cdk2 kinase activity was first detected a few hours prior to the onset of DNA synthesis. Microinjection of anti-p33cdk2 antibodies blocked cells from entering S phase. Pre-adsorption of these antibodies with cdk2 protein abrogated their blocking effect suggesting that the G1 arrest caused by these antibodies is cdk2-specific. These results indicate that p33cdk2 is required for the G1-to-S phase transition in mammalian cells. We also show evidence to suggest that the cyclin E/p33cdk2 complex is likely to be required for entry into S phase since the timing of the cyclin E-associated kinase activity was coincident with that of p33cdk2 and preclearing of either component abolished the majority of the histone H1 kinase activity present in the lysates harvested from the late G1.

The adenovirus E1A-associated kinase consists of cyclin E-p33cdk2 and cyclin A-p33cdk2

The adenovirus E1A oncoproteins form stable complexes with several cellular proteins. Association of E1A with these proteins has been shown to be important for the oncogenic potential of E1A. Several of these proteins have been identified and include the product of the retinoblastoma gene and a key cell cycle regulatory protein, cyclin A. E1A also associates with a potent histone H1 kinase. The two major components of this activity are the cyclin E-p33cdk2 and cyclin A-p33cdk2 complexes. Both the cyclin E-p33cdk2 and cyclin A-p33cdk2 complexes have been implicated in regulatory events controlling entry into or passage through DNA synthesis. Although the architecture of such interactions remains unclear, it is likely that by targeting such complexes, adenovirus is affecting some aspect of cell cycle control.

Cyclin E/cdk2 and cyclin A/cdk2 kinases associate with p107 and E2F in a temporally distinct manner

Cyclin E is classified as a putative G1 cyclin on the basis of its cyclic pattern of mRNA expression, with maximal levels being detected near the G1/S boundary. We report here that cyclin E is found associated with the transcription factor E2F in a temporally regulated fashion. E2F is known to be a critical transcription factor for the expression of some S phase-specific proteins and is thought to be important for a series of others. Antisera specific for cyclin E were raised and used to demonstrate an association between cyclin E and E2F. This cyclin E/E2F complex was seen in a variety of human cell lines from various tissues, but its appearance was detected primarily during the G1 phase of the cell cycle. The cyclin E/E2F association decreased as cells entered S phase, just as the association of E2F with cyclin A became detectable. We characterized the cyclin E-E2F complex further to show that both the cyclin-dependent kinase-2 (cdk2) and p107 were present. Therefore, the p107/E2F complex is associated with two different cdk2 kinase complexes--one containing cyclin A and the other containing cyclin E--and the appearance of these complexes is temporally regulated during the cell cycle. The presence of cyclin E/E2F complexes in the G1 phase suggests a role for cyclin E in the control of genes required for the G1-to-S transition.

Association of human cyclin E with a periodic G1-S phase protein kinase

G1 cyclins control the G1 to S phase transition in the budding yeast, Saccharomyces cerevisiae. Cyclin E was discovered in the course of a screen for human complementary DNAs that rescue a deficiency of G1 cyclin function in budding yeast. The amounts of both the cyclin E protein and an associated protein kinase activity fluctuated periodically through the human cell cycle; both were maximal in late G1 and early S phases. Cyclin E-associated kinase activity was correlated with the appearance of complexes containing cyclin E and the cyclin-dependent kinase Cdk2. Thus, the cyclin E-Cdk2 complex may constitute a human G1-S phase-specific regulatory protein kinase.

Transformation of primary BRK cells by human papillomavirus type 16 and EJ-ras is increased by overexpression of the viral E2 protein

The close association between human papillomavirus type 16 (HPV-16) and cervical cancer implies some role for the virus in the development of this disease. Recent studies have shown that HPV-16, under the control of strong heterologous promoters, can cooperate with the activated ras oncogene to transform primary baby rat kidney cells. Virus types associated with benign lesions, e.g. HPV-6 and -11, do not function in this system. The discrimination between virus types associated with benign and tumorigenic lesions by this assay implicate it as a useful system for the study of transformation in vitro. The studies reported here investigate the activity of the HPV-16 early gene product E2 in transformation. In the presence of exogenous E2, endogenous viral promoters are stimulated sufficiently to give a high efficiency of transformation in primary epithelial cells. This transactivation by E2 obviates the need for heterologous promoters, and implicates increased viral gene expression as a prerequisite for transformation. The stimulatory effect of E2 appears to be mediated through increased levels of expression of the E7 protein, which has been shown in similar assays to be sufficient to give transformation in cooperation with ras. CAT assays confirm that HPV-16 E2 can transactivate the HPV-16 early promoters. These studies demonstrate some of the elements in a complex series of events likely to be involved in the development of cervical carcinomas.

Gorgoderina alobata sp.nov.(Trematoda: Gorgoderidae) from the toad Bombina variegata

A bladder fluke from the toad Bombina variegata is described and erected as a new species under the name of Gorgoderina alobata sp.nov. A comparison is made between this trematode and G. carli Baer, 1930, from India. It is also compared with the other two previously described European species, G. vitelliloba (Olsson, 1876) and G. skrjabini Pigulevsky, 1953.