Transforming growth factor beta(1) selectively inhibits the cyclic AMP-dependent proliferation of primary thyroid epithelial cells by preventing the association of cyclin D3-cdk4 with nuclear p27(kip1)

Dog thyroid epithelial cells in primary culture constitute a physiologically relevant model of positive control of DNA synthesis initiation and G0-S prereplicative phase progression by cAMP as a second messenger for thyrotropin (thyroid-stimulating hormone [TSH]). As previously shown in this system, the cAMP-dependent mitogenic pathway differs from growth factor cascades as it stimulates the accumulation of p27(kip1) but not cyclins D. Nevertheless, TSH induces the nuclear translocations and assembly of cyclin D3 and cdk4, which are essential in cAMP-dependent mitogenesis. Here we demonstrate that transforming growth factor beta(1) (TGFbeta(1)) selectively inhibits the cAMP-dependent cell cycle in mid-G1 and various cell cycle regulatory events, but it weakly affects the stimulation of DNA synthesis by epidermal growth factor (EGF), hepatocyte growth factor, serum, and phorbol esters. EGF+serum and TSH did not interfere importantly with TGFbeta receptor signaling, because they did not affect the TGFbeta-induced nuclear translocation of Smad 2 and 3. TGFbeta inhibited the phosphorylation of Rb, p107, and p130 induced by TSH, but it weakly affected the phosphorylation state of Rb-related proteins in EGF+serum-treated cells. TGFbeta did not inhibit c-myc expression. In TSH-stimulated cells, TGFbeta did not affect the expression of cyclin D3, cdk4, and p27(kip1), nor the induced formation of cyclin D3-cdk4 complexes, but it prevented the TSH-induced relocalization of p27(kip1) from cdk2 to cyclin D3-cdk4. It prevented the nuclear translocations of cdk4 and cyclin D3 without altering the assembly of cyclin D3-cdk4 complexes probably formed in the cytoplasm, where they were prevented from sequestering nuclear p27(kip1) away from cdk2. This study dissociates the assembly of cyclin D3-cdk4 complexes from their nuclear localization and association with p27(kip1). It provides a new mechanism of regulation of proliferation by TGFbeta, which points out the subcellular location of cyclin D-cdk4 complexes as a crucial factor integrating mitogenic and antimitogenic regulations in an epithelial cell in primary culture.

Cell cycle regulators in testicular cancer: loss of p18INK4C marks progression from carcinoma in situ to invasive germ cell tumours

Cell cycle regulators govern cellular proliferation, modulate differentiation and, when defective, contribute to oncogenesis. Here, we examined expression of cyclins A, B1 and E, and cyclin-dependent kinase (CDK) inhibitors p18INK4C (p18), p21WAF1/Cip1 (p21) and p27KiP1 (p27), in normal human adult testis (n = 5), and 53 testicular tumours, including 23 carcinomas in situ (CIS) and 30 germ cell tumours (GCTs). Immunohistochemical analysis revealed a correlation between proliferation and abundance of the cyclin proteins, and abundant p18 and the lack of p21 and p27 in normal spermatogenesis. Expression of p21 and/or p27 was induced in some differentiated structures seen in teratomas, and was recapitulated in cell culture, using human NTera2/D1 teratocarcinoma cells induced to differentiate into neurons. CIS lesions showed abundant p18, low cyclin E, and moderate p27, in contrast with most invasive seminomas and embryonal carcinomas with very low-to-negative p18, often elevated cyclin E, and, unexpectedly, sustained or increased p27. Our results suggest increased abundance of cyclin E, and particularly downmodulation or loss of p18INK4C as the features that correlate with progression from CIS to invasive germ cell tumours of the human testis.

Monoclonal antibody probes for p21WAF1/CIP1 and the INK4 family of cyclin-dependent kinase inhibitors

Inhibition of cyclin dependent kinases (cdk) by proteins of two families of cdk inhibitors (CKIs) represents one of the key modes of cell-cycle control. Although not fully understood at present, the functions of the individual members of the Cip/Kip and INK4 families of CKIs have been implicated in fundamental biological processes as diverse as cellular proliferation, responses to genotoxic stress, regulation of cellular differentiation, and senescence. In addition, the seven currently known CKIs qualify as either established or candidate tumor suppressors whose loss or inactivation contribute to molecular pathogenesis of a wide range of tumor types. In this study, we report the isolation and characterization of a panel of 10 mouse monoclonal antibodies (MAbs) that specifically recognize p21WAF1/CIP1 (p21) or the individual members of the INK4 family of CKIs: p15INK4b (p15), p16INK4a (p16), p18INK4c (p18), or p19INK4d (p19). These antibodies are proving to be invaluable molecular probes for analyses of protein abundance, subcellular localization, interacting cellular proteins, and ultimately the function(s) of these cell cycle regulators. Epitopes targeted by the antibodies were mapped by peptide enzyme-linked immunoadsorbent assay (ELISA), and performance of the MAbs assessed in a range of immunochemical techniques. Individual MAbs of our series recognize distinct pools of the respective CKIs, a feature reflected by their differential applicability in immunoblotting, immunoprecipitation, and immunostaining including immunohistochemistry on archival paraffin-embedded tissue sections. Together, these antibodies represent useful reagents to study CKIs in cells and tissues, a set of tools that should help elucidate the physiological roles played by the individual CKIs, and better understand the molecular mechanisms of loss or inactivation of these (candidate) tumor suppressors in human malignancies.

Evolution of shape complementarity and catalytic efficiency from a primordial antibody template

The crystal structure of an efficient Diels-Alder antibody catalyst at 1.9 angstrom resolution reveals almost perfect shape complementarity with its transition state analog. Comparison with highly related progesterone and Diels-Alderase antibodies that arose from the same primordial germ line template shows the relatively subtle mutational steps that were able to evolve both structural complementarity and catalytic efficiency.

Cyclin D3 accumulation and activity integrate and rank the comitogenic pathways of thyrotropin and insulin in thyrocytes in primary culture

The proliferation of most normal cells depends on the synergistic interaction of several growth factors and hormones, but the cell cycle basis for this combined requirement remains largely uncharacterized. We have addressed the question of the requirement for insulin/IGF-1 also observed in many cell culture systems in the physiologically relevant system of primary cultures of dog thyroid epithelial cells stimulated by TSH, which exerts its mitogenic activity only via cAMP. The induction of cyclin A and cdc2, the phosphorylation of cdk2, the nuclear translocation of cdk4 and the assembly of cyclin D3-cdk4 complexes required the synergy of TSH and insulin. Cyclin D3 (the most abundant cyclin D) was necessary for the proliferation stimulated by TSH in the presence of insulin as shown by microinjection of a neutralizing antibody. Cyclin D3 accumulation and activity were differentially regulated by insulin and TSH, which points out this cyclin as an integrator that ranks these comitogenic pathways as supportive and activatory, respectively. Paradoxically TSH alone strongly repressed cyclin D3 accumulation. This inhibition was overridden by insulin, which markedly stimulated cyclin D3 mRNA and protein accumulation, but failed to assemble cyclin D3-cdk4 complexes in the absence of TSH. TSH unmasked the DCS-22 epitope of cyclin D3 and assembled cyclin D3-cdk4 in the presence of insulin. These data demonstrate that cyclin D synthesis and cyclin D-cdk assembly can be dissociated and complementarily regulated by different agents and signalling pathways.

Accumulation of cyclin B1 requires E2F and cyclin-A-dependent rearrangement of the anaphase-promoting complex

In mammalian somatic-cell cycles, progression through the G1-phase restriction point and initiation of DNA replication are controlled by the ability of the retinoblastoma tumour-suppressor protein (pRb) family to regulate the E2F/DP transcription factors. Continuing transcription of E2F target genes beyond the G1/S transition is required for coordinating S-phase progression with cell division, a process driven by cyclin-B-dependent kinase and anaphase-promoting complex (APC)-mediated proteolysis. How E2F-dependent events at G1/S transition are orchestrated with cyclin B and APC activity remains unknown. Here, using an in vivo assay to measure protein stability in real time during the cell cycle, we show that repression of E2F activity or inhibition of cyclin-A-dependent kinase in S phase triggers the destruction of cyclin B1 through the re-assembly of APC, the ubiquitin ligase that is essential for mitotic cyclin proteolysis, with its activatory subunit Cdh1. Phosphorylation-deficient mutant Cdh1 or immunodepletion of cyclin A resulted in assembly of active Cdh1-APC even in S-phase cells. These results implicate an E2F-dependent, cyclin A/Cdk2-mediated phosphorylation of Cdh1 in the timely accumulation of cyclin B1 and the coordination of cell-cycle progression during the post-restriction point period.

Direct induction of cyclin D2 by Myc contributes to cell cycle progression and sequestration of p27

Ectopic expression of Myc induces Cdk2 kinase activity in quiescent cells and antagonizes association of p27(kip1) with Cdk2. The target gene(s) by which Myc mediates this effect is largely unknown. We now show that p27 is rapidly and transiently sequestered by cyclin D2-Cdk4 complexes upon activation of Myc and that cyclin D2 is a direct target gene of Myc. The cyclin D2 promoter is repressed by Mad-Max complexes and de-repressed by Myc via a single highly conserved E-box element. Addition of trichostatin A to quiescent cells mimics activation of Myc and induces cyclin D2 expression, suggesting that cyclin D2 is repressed in a histone deacetylase-dependent manner in quiescent cells. Inhibition of cyclin D2 function in established cell lines, either by ectopic expression of p16 or by antibody injection, inhibits Myc-dependent dissociation of p27 from Cdk2 and Myc-induced cell cycle entry. Primary mouse fibroblasts that are cyclin D2-deficient undergo accelerated senescence in culture and are not immortalized by Myc; induction of apoptosis by Myc is unimpaired in such cells. Our data identify a downstream effector pathway that links Myc directly to cell cycle progression.

B cell antigen receptor-mediated activation of cyclin-dependent retinoblastoma protein kinases and inhibition by co-cross-linking with Fc gamma receptors

Cross-linking the B cell Ag receptor (BCR) to surface Fc receptors for IgG (Fc gamma R) inhibits G1-to-S progression; the mechanism by which this occurs is not completely known. We investigated the regulation of three key cell cycle regulatory components by BCR-Fc gamma R co-cross-linking: G1-cyclins, cyclin-dependent kinases (Cdks), and the retinoblastoma gene product (Rb). Rb functions to suppress G1-to-S progression in mammalian cells. Rb undergoes cell-cycle-dependent phosphorylation, leading to its inactivation and thereby promoting S phase entry. We demonstrate in this paper for the first time that BCR-induced Rb phosphorylation is abrogated by co-cross-linking with Fc gamma R. The activation of Cdk4/6- and Cdk2-dependent Rb protein kinases is concomitantly blocked. Fc gamma R-mediated inhibition of Cdk2 activity results in part from an apparent failure to express Cdk2 protein. By contrast, inhibition of Cdk4/6 activities is not due to suppression of Cdk4/6 or cyclins D2/D3 expression or inhibition of Cdk-activating kinase activity. Cdk4- and Cdk6-immune complexes recovered from B cells following BCR-Fc gamma R co-cross-linking are devoid of coprecipitated D-type cyclins, indicating that inhibition of their Rb protein kinase activities is due in part to the absence of bound D-type cyclin. Thus, BCR-derived activation signals that up-regulate D-type cyclin and Cdk4/6 protein expression remain intact; however, Fc gamma R-mediated signals block cyclin D-Cdk4/6 assembly or stabilization. These results suggest that assembly or stabilization of D-type cyclin holoenzyme complexes 1) is an important step in the activation of Cdk4/6 by BCR signals, and 2) suffice in providing a mechanism to account for inhibition of BCR-stimulated Rb protein phosphorylation by Fc gamma R.

p16INK4a, but not constitutively active pRb, can impose a sustained G1 arrest: molecular mechanisms and implications for oncogenesis

p16ink4 and pRb, two components of a key G1/S regulatory pathway, and tumor suppressors commonly targeted in oncogenesis, are among the candidates for gene therapy of cancer. Wild-type p16 and a constitutively active pRb(delta cdk) mutant both blocked G1 in short-term experiments, but only p16 imposed a sustained G1 arrest. Unexpectedly, cells conditionally exposed to pRb(delta cdk) entered S phase after 2 days, followed by endoreduplication between days 4-6. The distinct phenotypes evoked by p16 vs pRb(delta cdk) appear mediated by cyclin E/CDK2 which, while active in the pRb(delta cdk)-expressing cells, became rapidly inhibited through restructuring diverse cyclin/CDK/p21 complexes by p16. These results provide novel insights into the roles of p16, pRb and cyclin E in G1/S control and multistep oncogenesis, with implications for gene therapy strategies.

Early induction of cyclin D2 expression in phorbol ester-responsive B-1 lymphocytes

B-1 lymphocytes represent a distinct B cell subset with characteristic features that include self-renewing capacity and unusual mitogenic responses. B-1 cells differ from conventional B cells in terms of the consequences of phorbol ester treatment: B-1 cells rapidly enter S phase in response to phorbol ester alone, whereas B-2 cells require a calcium ionophore in addition to phorbol ester to trigger cell cycle progression. To address the mechanism underlying the varied proliferative responses of B-1 and B-2 cells, we evaluated the expression and activity of the G1 cell cycle regulator, cyclin D2, and its associated cyclin-dependent kinases (Cdks). Cyclin D2 expression was upregulated rapidly, within 2-4 h, in phorbol ester-stimulated B-1 cells, in a manner dependent on intact transcription/translation, but was not increased in phorbol ester- stimulated B-2 cells. Phorbol ester-stimulated cyclin D2 expression was accompanied by the formation of cyclin D2-Cdk4, and, to a lesser extent, cyclin D2-Cdk6, complexes; cyclin D2- containing complexes were found to be catalytically functional, in terms of their ability to phosphorylate exogenous Rb in vitro and to specifically phosphorylate endogenous Rb on serine780 in vivo. These results strongly suggest that the rapid induction of cyclin D2 by a normally nonmitogenic phorbol ester stimulus is responsible for B-1 cell progression through G1 phase. The ease and rapidity with which cyclin D2 responds in B-1 cells may contribute to the proliferative features of this subset.

Immunohistochemical analysis of the D-type cyclin-dependent kinases Cdk4 and Cdk6, using a series of monoclonal antibodies

Cellular signal transduction cascades triggered by mitogenic or antiproliferative cues eventually converge on a biochemical mechanism centered around the retinoblastoma tumor suppressor (pRb), the so-called RB pathway that governs G1-phase progression and guards the commitment to enter S phase. pRb, together with its immediate upstream regulators, the D-type cyclins, their partner cyclin-dependent kinases Cdk4 and Cdk6, and the Cdk inhibitors, form a functional unit that is involved in major decisions about cellular fate, and whose components, including the proto-oncogenic cyclin D-dependent kinases, are commonly deregulated in many types of cancer. We report here the production and characterization of a series of 12 monoclonal antibodies (MAbs) that specifically recognize either Cdk4 or Cdk6. These antibodies are proving to be invaluable molecular probes for defining abundance, subcellular localization, binding partners, and ultimately the function(s) of these cell cycle-regulatory kinases. Localization of the target epitopes was mapped by peptide enzyme-linked immunoadsorbent assay (ELISA), and two antibodies recognizing sequences adjacent to N-terminus of Cdk4 can discriminate between the wild-type protein and the oncogenic, melanoma-associated R24C mutant of this kinase. Individual antibodies of our panel recognize distinct pools of Cdk4/6, a feature reflected by their differential applicability in immunoblotting, immunoprecipitation, kinase assays, and immunostaining including immunohistochemistry on archival paraffin-embedded tissue sections. Collectively, the antibodies described in this study provide the means for immunochemical analyses of the cyclin D-dependent kinases in human and animal cells, and represent useful molecular tools that should help better understand the biological roles of Cdk4 and Cdk6 in normal cell-cycle control, and their oncogenic activity in tumor cells.

Centrosome duplication in mammalian somatic cells requires E2F and Cdk2-cyclin A

Centrosome duplication is a key requirement for bipolar spindle formation and correct segregation of chromosomes during cell division. In a manner highly reminiscent of DNA replication, the centrosome must be duplicated once, and only once, in each cell cycle. How centrosome duplication is regulated and coordinated with other cell-cycle functions remains poorly understood. Here, we have established a centrosome duplication assay using mammalian somatic cells. We show that centrosome duplication requires the activation of E2F transcription factors and Cdk2-cyclin A activity.

[Leptinemia in individuals with hypertension (pilot study)]

During the last decade several papers were published where obesity in included among the building stones of the so-called metabolic cardiovascular syndrome (along with hypertension, dyslipidaemia, impaired glucose tolerance and hyperinsulinaemia). Several months ago it was also revealed that some patients with the metabolic syndrome suffer from hyperleptinaemia. Leptinaemia is considered by some authors as independent indicator of the risk of accelerated atherosclerosis. The cause of these hypothesis were (in addition to the known conclusions on the occurrence frequent incidence of leptin resistance and insulin resistance) in particular the results of experimental studies where evidence was provided that infusion induced hyperleptinaemia leads in animals to hypertension due to its direct effect on sympathicotonia and peripheral vascular resistance. The authors of these hypothesis assume that hyperleptinaemia (in particular in subjects with metabolic syndrome) in one of the basic causes of hypertension which is frequently encountered in these patients.

OBJECTIVE

To assess the relations between leptinaemia and the blood pressure reading (actual and mean values) and leptinaemia and the classification of hypertension according to WHO.

METHOD

The authors examined 35 hypertensive subject and 10 subject with tetanies (without hypertension). The blood pressure was assessed under standard conditions (rest, semi-recumbent position, three readings). The mean blood pressure readings during the last three months were obtained from case records. Leptin was assessed by the ELISA method of Bio Vendor Co.

RESULTS

The group of hypertonic can be classified as subjects with mild obesity (BMI 30.1). The values of leptin were elevated but did not differ significantly from those of the normal population. No correlations were found between leptinaemia (incl. values calculated for BMI) and the actual and mean blood pressure readings. No correlations were found between leptinaemia (incl. BP calculated with regard to BMI) and the stage of hypertension according to WHO.

CONCLUSION

Hypertonic subject do not differ significantly as to the serum leptin concentration from the general population. Leptinaemia does not correlate with the actual or mean blood pressure reading nor with stage of hypertension according to the WHO classification. Thus the authors did not confirm the hypothesis on the fundamental effect of leptinaemia on the genesis and development of hypertension. It is probable that leptin is only one of the many factors which have an impact on blood pressure.

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.

[Leptinaemia in the Czech population]

INTRODUCTION

Leptin is a protein, determined by the ob-gene which influences in a fundamental way the energy metabolism of the organism. A significant effect of leptin on the haematopoietic, immunological and endocrinological system cannot be ruled out nor its effect on the course of pregnancy and maturation of the organism. In humans leptinaemia correlates with the amount of subcutaneous fat which is due to a receptor or post-receptor disorder, obese subjects suffer frequently from hyperleptinaemia.

OBJECTIVE

To assess the mean leptinaemia of the general population, seek relations between leptinaemia and anthropological indicators and age.

METHODS

Using the method of random sampling the authors examined a group of 538 probands (252 males, 286 females) incl. 12% healthy students of the Faculty of Physical Culture in Olomouc, 37% subjects without acute or chronic complications feeling in good health and 37% patients of the metabolic and diabetological ambulance of the hospital in Sternberk. In each patient a detailed case-history was recorded, an anthropological examination was made and a venous blood sample was taken for leptin analysis (serum, ELISA-sandwich method of BIOVENDOR Co.)

RESULTS

Spectrum of patients, whose condition and age distribution in our group corresponded to the general population of the Czech Republic. The mean age of the probands was 51 years (18 to 82 years), the examined group can be characterized as subjects lacking signs of obesity. Leptinaemia was on average about 10 ng/ml (minimum 0, maximum 97.9 ng/ml), whereby men had values round 6 and women round 14 ng/ml (women had also a greater adipose tissue mass). Non-obese subjects (BMI<26) had a mean leptinaemia of 5 (women cca 6, men cca 2 ng/ml), obese subjects (BMI>30) have a leptinaemia of cca 19 ng/ml (women about 26, men about 13 ng/ml). With advancing age the leptinaemia in adults rises up to the age of 70, in subjects above 70 years it does not change (in women it declines significantly). The dynamics of leptinaemia imitate the changes of BMI and percentage of adipose tissue (in men also a rise in WHR). Leptinaemia is associated with the BMI (correlation coefficient 0.55), with the percentage of body fat (correlation coefficient 0.75), and in men with the WHR (correlation coefficient 0.82). The association between ageand leptinaemia is only indicated (correlation coefficient 0.29) and is not very close. According to the authors results subcutaneous body fat is responsible for cca 60% of the variability of leptinaemia (in women as much as 74%), BMI for 23%, age and sex for cca 9% of the vriability of leptinaemia. In men the WHR is responsible for 66% of the variability of leptinaemia. With an increase of subcutaneous adipose tissue by 1% the leptinaemia increases by some 0.54 ng/ml (in men by 0.22 ng/ml, in women by 0.84 ng/ml), with increasing BMI leptinaemia rises by 0.44 ng/ml/u (in men by 1.3 ng/ml, in women by 1.72 ng/ml), with advancing age leptin rises by 0.24 ng/ml/year (in men by 0.16 ng/ml, in women by 0.28 ng/ml), changes of leptinaemia imitate changes of BMI and the percentage of body fat. With increasing WHR in men the leptinaemia rises by 2.6 ng/ml/0.1 WHR.

CONCLUSION

Standards of leptinaemia for the general population of the Czech Republic were elaborated. Leptinaemia correlates most closely of all anthropometric indicators with subcutaneous fat and in men with the WHR index. With advancing age between 20 and 70 years leptunaemia rises and then decliunes insignificantly (in women the changes are however significant). The primary cause of the mentioned differencesare probably changes of the bodily constitution.

Activation of cyclin A gene expression by the cyclin encoded by human herpesvirus-8

Human herpesvirus-8 (HHV-8), also known as Kaposi's sarcoma-associated herpesvirus, encodes a protein, referred to as HHV8-Vcyc, with sequence similarity to human G1 cyclins, in particular of the D type. HHV8-Vcyc is expressed in Kaposi's sarcoma and functional analysis suggests that it can activate cyclin-dependent kinases (cdk) and thereby trigger inactivation of the retinoblastoma protein (pRb), indicating that HHV8-Vcyc may contribute to the oncogenic potential of HHV-8. We show here that HHV8-Vcyc can activate transcription of the human cyclin A gene in quiescent cells, a property shared with known transforming oncogenes. Transcriptional activation by HHV8-Vcyc depends on an E2F-binding site in the cyclin A promoter, and cdk6 kinase activity is required. The ability of HHV8-Vcyc to activate cyclin A gene expression is shared by D-type cyclins and cyclin E. Unlike D-type cyclins, HHV8-Vcyc is unable to trigger phosphorylation of the pRb-related protein p107 and fails to induce dissociation of p107 from E2F. Unlike cyclin E, HHV8-Vcyc fails to interact physically with E2F complexes on the cyclin A promoter. These results provide additional evidence for the notion that the HHV-8-encoded cyclin differs in several properties from cellular G1 cyclins.

[Use of proinsulin analysis for estimates of insulin resistance]

INTRODUCTION

According to contemporary estimates diabetes is present in 120 million subjects. This disease is associated with the incidence of a number of very serious organ complications and very frequently is diagnosed late (several years after its development). Because despite increased diagnostic and therapeutic efforts the number of diabetic patients is increasing, new diagnostic and therapeutic means are sought. Evidence was provided that some complications of diabetes develop not only in case of poor compensation but also in hyperinsulinaemia (hypertension, ischaemic heart and coronary artery disease etc.). In clinical practice it is however possible to assess hyperinsulinaemia or incipient insulin resistance only with difficulty because classical examinations (insulin and C-peptide on fasting) have a very low specificity and sensitivity. Therefore for estimation of insulin resistance loading tests are used (e.g. examination of insulin after stimulation with glucose, or C-peptide after stimulation with glucagon, insulin tolerance and suppression tests, or in research projects so-called minimal models or clamp techniques). Any loading test is however demanding from the aspect of time, money, technical aspects and staff and therefore possibilities are sought how to estimate the degree of insulin resistance and sensitivity in a specimen of biological material under basal conditions. OBJECTIVE OF INVESTIGATION: Because in the literature only sporadically assessment of intact proinsulin is mentioned as the ideal marker of insulin resistance under basal conditions, the authors decided to assess the relations between intact proinsulin (PI) and other biochemical parameters in patients with type 2 diabetes and dyslipidaemia (200 probands) and to assess whether PI correlates with the results of loading tests (modified oGTT with calculation of the sum and delta-insulin--120 probands).

RESULTS

It was revealed that PI (contrary to insulin, C-peptide and total proinsulin) correlates with the results of the loading test characterizing insulin resistance (sum and delta insulin, correlation coefficient 0.84) (n=120 subjects). It was furthermore found that probands (n=200 subjects) who are followed up on account of type 2 diabetes or dyslipidaemia (or both) differ from the control group (n=20 subjects) as regards biochemical parameters only in the PI concentration (dispensarized patients have higher levels, p>0.99), whereby in other standard basal characteristics of insulin secretion and resistance the groups did not differ. The differences were correlated with HOMA models of insulin secretion and resistance and no correlations were found. The PI concentration in this group correlated significantly with the cholesterol, fibrinogen and triacylglycerol concentration. No relations were found between the values of intact proinsulin with C-peptide and insulin.

CONCLUSION

Based on the results of their study the authors assume that examination of intact proinsulin is a valid "basal" indicator of insulin resistance. From the results ensues also that intact proinsulin is probably a very good predictor as regards the risk of development of cardiovascular disease.

Dissecting functions of the retinoblastoma tumor suppressor and the related pocket proteins by integrating genetic, cell biology, and electrophoretic techniques

The members of the 'pocket protein' family, comprising the retinoblastoma tumor suppressor (pRB) and its relatives, p107 and p130, negatively regulate cell proliferation and modulate fundamental biological processes including embryonic development, differentiation, homeostatic tissue renewal, and defense against cancer. The large, multidomain pocket proteins act by binding a plethora of cell fate-determining and growth-stimulatory proteins, the most prominent of which are the E2F/DP transcription factors. These protein-protein interactions are in turn regulated by carefully orchestrated phosphorylation events on multiple serine and threonine residues of pRB, p107, and p130, events which are carried out, at least in part, by the cyclin-dependent kinases that form the key elements of the cell cycle machinery. Here we discuss the recently obtained new insights into the diverse functions of the pRB family, and show examples of how integration of genetic, cell biology, and a range of electrophoretic approaches help to advance our understanding of the biological roles played by the pocket proteins in both normal and cancer cells.

Phosphorylation of mammalian CDC6 by cyclin A/CDK2 regulates its subcellular localization

Cyclin-dependent kinases (CDKs) are essential for regulating key transitions in the cell cycle, including initiation of DNA replication, mitosis and prevention of re-replication. Here we demonstrate that mammalian CDC6, an essential regulator of initiation of DNA replication, is phosphorylated by CDKs. CDC6 interacts specifically with the active Cyclin A/CDK2 complex in vitro and in vivo, but not with Cyclin E or Cyclin B kinase complexes. The cyclin binding domain of CDC6 was mapped to an N-terminal Cy-motif that is similar to the cyclin binding regions in p21(WAF1/SDI1) and E2F-1. The in vivo phosphorylation of CDC6 was dependent on three N-terminal CDK consensus sites, and the phosphorylation of these sites was shown to regulate the subcellular localization of CDC6. Consistent with this notion, we found that the subcellular localization of CDC6 is cell cycle regulated. In G1, CDC6 is nuclear and it relocalizes to the cytoplasm when Cyclin A/CDK2 is activated. In agreement with CDC6 phosphorylation being specifically mediated by Cyclin A/CDK2, we show that ectopic expression of Cyclin A, but not of Cyclin E, leads to rapid relocalization of CDC6 from the nucleus to the cytoplasm. Based on our data we suggest that the phosphorylation of CDC6 by Cyclin A/CDK2 is a negative regulatory event that could be implicated in preventing re-replication during S phase and G2.

Determination of leptin receptor in the serum and relations to laboratory and anthropological parameters in patients with atherosclerotic complications

Leptin receptors are supposed to have signal effects and are located in most tissues in the organism but we failed to find literary data on concentration (measurement) of leptin receptors in the system circulation. We examined by the method of randomized selection the group of 20 patients with manifested atherosclerosis in whom BMI was calculated. Then we analyzed concentration of leptin receptor (double sandwich ELISA, standard recombinant human leptin), leptin, glucose, insulin, proinsulin, CRP and uric acid in the serum. The control group consisted of 103 probands without signs of atherosclerosis or other manifested diseases. The control group was subjected to determination of BMI, leptin and leptin receptor in the serum. Concentration of leptin receptor does not differ significantly between the patients with atherosclerosis and normal population. Probands with atherosclerosis showed a very close negative correlation between concentration of leptin receptor and leptinemia which is absent in normal population.

Perspective: defects in cell cycle control and cancer

The past several years have witnessed a dramatic accumulation of experimental and clinical evidence supporting the notion that the cell cycle machinery is commonly targeted on oncogenesis. While numerous cell cycle regulators qualify as proto-oncogenes or tumour suppressors and their aberrations may provide direct proliferative advantage to cancer cells, defects in checkpoint mechanisms act more indirectly yet affect both tumour progression and response to anticancer therapy. In this review, the ways that cell cycle defects contribute to oncogenesis are briefly illustrated and the emerging benefits of the newly gained insights into the cell cycle clock for clinical oncology are critically considered. Given the many reviews on the subject, emphasis is put on concepts rather than comprehensive treatment of the selected topics, with particular attention given to controversial issues, unorthodox phenomena, and the challenge facing the 'cell cycle and cancer field' at the transition to the next millennium.

[Benefit of direct determination of LDL-cholesterol (comparison with LDL measurement using calculated estimates]

Treatment of dyslipidemia and its frequently associated complications (manifest atherosclerosis) is very pretentious from the economic aspect. Diagnostic and therapeutic criteria are based mainly on biochemical analyses. Although demands on laboratories are relatively strict (respecting defined laboratory errors, analytical and preanalytical conditions), when defined diagnostic criteria are used, the results of biochemical analyses are not yet satisfactory. A typical example is the stratification of risk patients according to the LDL concentration which in our country is very often preferred, although the LDL concentration is based only on calculation (contrary to investigations from which the majority of recommendations was derived where the LDL concentration was assessed directly). We know from our own experience that a large percentage of results of estimated and assessed LDL differs significantly. Therefore we wanted to know whether the assessed LDL concentration correlates with its estimate according to Friedewald s formula and which analytes have the greatest impact on the LDL concentration. Our objective was also to assess th percentage of incorrectly listed patients (according to the LDL stratification scale). In 1997-1998 we examined a group of 4578 probands, patients of the consultant out-patient departments of the Sternberk hospital. Their mean age was 56 years. On average subjects with as slightly atherogenic phenotype were involved (classification A according to EAS). The values of lipid parameters did not differ significantly in the two sexes. The cholesterol, LDL and triacylglycerol concentrations increased with advancing age. The LDL values obtained by assessment and calculation correlated closely. The LDL value was influenced most by ApoB and total cholesterol. Triacylglycerols correlated with LDL assessment only up to a concentration of .3 mmol/l. HDL, ApoA-1 and higher triacylglycerol concentrations (1.3 mmol/l) did not correlate with the LDL value. The authors provided evidence that in subjects where it was possible to calculate LDL lege artis (2458 probands) were listed according to LDL calculation into a wrong group (stratification according to NCEP) whereby up to an LDL concentration .11 mmol/l this parameter cannot be predicted at all by calculation (error up to 85%). A satisfactory estimate is assumed only at LDL concentrations 5.2 mmol/l. Because the estimated LDL values are in the majority of patients lower than the calculated values, it may be assumed that during stratification of LDL obtained by calculation the patients are treated too aggressively. Assuming pharmacological treatment of all mentioned patients, it may be estimated that by using analyses of direct LDL for stratification of probands the costs of hypolipidaemic treatment will by reduced by about 1/4-1/3 (in the catchment area of the Sternberk hospital this would save more than 10 million crowns). The costs of LDL analyses per year are about 180,000 crowns (in the Sternberk hospital--which amounts to cca 1.5% of the money saved on pharmacotherapy).

p21WAF1/CIP1 mutants deficient in inhibiting cyclin-dependent kinases (CDKs) can promote assembly of active cyclin D/CDK4(6) complexes in human tumor cells

The cyclin-dependent kinase (CDK) inhibitor p21WAF1/CIP1 is a multidomain, multifunctional protein and a candidate tumor suppressor. Here, we show that, among rationally designed and tumor-associated mutants of human p21 ectopically expressed in U-2-OS cells, those that are selectively deficient in binding to either cyclin or CDK are partially impaired in inhibiting endogenous CDK activities but efficiently promote assembly of active cyclin D/CDK4(6) complexes. These results provide mechanistic insights into the p21-cyclin/CDK interplay in vivo and suggest a functional subclassification of tumor-specific aberrations of p21. Intriguingly, the subclass exemplified by the melanoma-derived N50S mutant may promote tumorigenesis, by both attenuating CDK-inhibitory function and concomitantly activating the proto-oncogenic cyclin D-dependent kinases.

Predicted anti-oestrogen resistance in BRCA-associated familial breast cancers

There is controversy concerning the prognosis of breast cancers arising in women carrying loss of function mutations in the breast cancer susceptibility genes BRCA1 and BRCA2. This study was carried out to assess the likely hormone dependence of this group of tumours in comparison with an age and grade matched group of control sporadic tumours. We used quantitative immunohistochemical analysis for the oestrogen receptor (ER), progesterone receptor (PgR), cyclin D1 and pS2 on sections of primary tumours and ductal carcinoma in situ (DCIS). Expression of PgR (P < 0.05) and cyclin D1 (P < 0.01) was low in the BRCA1- and BRCA2-associated cancers compared with sporadic cases. The low frequency of expression of ER (9/40), PgR (2/40) cyclin D1 (5/36) and pS2 (5/36) in the familial tumours indicates that the majority of such tumours will be oestrogen insensitive and unlikely to respond to hormonal manipulation even at the in situ stage in their evolution. The low level of PgR (2/40 cases) suggests that there may be some abnormality of transactivating function of the ER in these tumours.

[Serum leptin, early atherosclerosis and hypolipidemia (a new, previously undescribed effect of pravastatin, a hypolipemic agent)]

Hyperleptinemia is considered to be one of predictors of early atherosklerosis complications. This stimulated us to investigate differences between leptinemia in persons with accelerated atherosclerosis and leptinemia in probands without atherosclerosis complications. The study also verified whether leptinemia and its relationship to other anthropometric and biochemical parameters can differ in hypolipemic-treated probands and hypolipemic-untreated individuals. We examined 89 probands with accelerated atherosclerosis. The controls were 20 persons without any signs of accelerated atherosclerosis. Probands with accelerated atherosclerosis had a slight hyperglycemia and were slightly obese, but they did not meet criteria of metabolic cardiovascular syndrome. No significant differences between both groups under study were found in terms of anthropometric and biochemical parameters (BMI, % body fat, glycemia, insulin, C-peptide, intact proinsulin, total proinsulin cholesterol, HDL, triglycerides, LDL, homeostatic model of insulin secretion and resistance). Leptin concentration was not different as well. Stratification into males and females showed that women had a significantly higher leptinemia and fat tissue mass. Other biochemical parameters were similar in both groups. We suppose that in individuals without signs of metabolic syndrome, leptinemia does not belong among predictors of accelerated atherosclerosis. The accelerated atherosclerosis persons were then divided into subgroups according to medication (28 probands--pravastatin Lipostat 20, 15 probands--phenofibrate Lipanthyl 200M, 9 probands--simvastatin Zocor 20, 47 probands--no hypolipemic medication). No significant differences between the groups were found in terms of the analysed anthropometric and biochemical parameters, except leptinemia. The pravastatin-medicated probands had a significantly lower leptinemia (significant at 99% significance level) which was evidently sex-related than other patients. The pravastatin-administered persons showed no correlation between leptinemia and body fat mass (in contrast to other groups where such a correlation was highly statistically significant). These findings can be explained by a still unclear effect of pravastatin on insulin metabolism and on other factors involved in leptin synthesis and elimination. Thus, a new therapeutic effect of pravastatin can be supposed. This may account for a highly favourable effect of pravastatin on reduced manifestations of atherosclerosis complications event at a low LDL cholesterol decrease (particularly in persons with metabolic cardiovascular syndrome).

[Serum leptin in women during the third trimester of pregnancy]

Leptin is a small protein produced mainly by adipocytes. Recently, its relationship to obesity has been studied extensively. It was proved that obese individuals have either relative or absolute leptin deficiency. Several years ago, leptin was found to be produced also by the placenta. This stimulated us to study relationship between leptinemia and placental hormones in 85 women in the second gravidity trimester. Within the prenatal screening, these pregnant women were subjected to analysis of AFP, hCG, SP-1 glycoprotein and leptin and the results obtained were processed statistically. The control group consisted of 20 nonpregnant women with tetany. Women in the second gravidity trimester were found to have a significantly higher leptinemia than nongravid women (even with respect to body weight). This may be due to a larger amount of adipose tissue during gravidity and also leptin-resistance. Moreover, we recorded a negative correlation between leptinemia related to body weight and concentration of SP-1 glycoprotein. This finding supports the presumption that mother's leptinemia correlated negatively in the second gravidity trimester with quality and quantity of the placental syncytiotrophoblast. Our findings can be explained as follows: the biological effect of leptin is metabolically unfavourable for the growth of the foetus and the placenta. An increased leptinemia with advancing gravidity can be caused by a larger fatty mass and an increased activity of adipocytes when leptin presence increases in system circulation but the organism begins to be leptin-resistant and an "unfavourable" metabolic effect fort the gravid woman and the foetus is not distinct. These findings thus support the hypothesis postulating the nonsignificance of leptin production in human placenta and on the contrary the necessity of leptin-resistance for foetus development from the metabolic point of view. Thus, a decreased leptinemia immediately before and after the delivery could be caused by the still unclear regulators of leptin sensitivity. This is again a metabolically highly favourable state (reduced appetite, decreased body weight, increased energy output and others).

[Leptinemia in persons with acute myocardial infarct]

The purpose of the study was to verify whether the currently reported relationship between leptinemia and adipose tissue mass can be applied to cases of acute coronary attack. An increased number of cytokines has been reported in severe acute myocardial infarctions so that correlation between cytokines and leptin was investigated. Correlation between standard coronary markers and leptinemia was also studied. We examined 48 probands, patients of the Coronary Unit, Hospital, Sternberk, who were hospitalized for acute myocardial infarction (AMI--16 probands) or for unstable angina pectoris (UAP--22 probands). The persons with AMI had leptinemia and a higher concentration of interleukine-6 (Il-6) and of cardial troponine-I (cTn-I) than individuals without coronary accident (UAP). Early after the acute coronary lesion, leptinemia in persons with AMI displayed a statistically significant positive correlation with concentration of interleukine-6 and subsequently of markers of coronary lesion severity (cTnI). No correlation between leptinemia and body weight was found in those probands. This study proved that leptinemia in the AMI individuals is influenced directly by concentration of cytokines which leads to leptin superproduction by fat cells and leptin resistance.

Expression of a p16INK4a-specific ribozyme downmodulates p16INK4a abundance and accelerates cell proliferation

The pl6INK4a tumor suppressor negatively regulates progression through the G1 phase of the mammalian cell cycle. To mimic the downmodulation of p16INK4a commonly seen in cancer, we designed and characterized a hammerhead ribozyme against exon E1alpha of the murine pl6INK4a transcript. Stable expression of the ribozyme in murine erythroleukemia (MEL) cells reduced the endogenous pl6INK4a protein by more than 70% and significantly accelerated cell cycle progression. The specificity and efficiency of our new ribozyme suggest its possible application in elucidating the role of p16INK4a in fundamental biological processes including homeostatic tissue renewal, protection against oncogenic transformation, and cellular senescence.

Cyclin D3: requirement for G1/S transition and high abundance in quiescent tissues suggest a dual role in proliferation and differentiation

The mammalian D-type cyclins D1, D2, and D3 activate the cyclin-dependent kinases CDK4 and CDK6 in G1 and thereby promote the cell's commitment to enter S phase. To elucidate the extent of functional overlap among the D-type cyclins, we have examined several aspects of the least characterized member of this subfamily of G cyclin proteins, cyclin D3. Microinjection of cyclin D3-neutralizing antibody inhibited G1/S transition in human (IMR-90) and rat (R12) diploid fibroblasts, indicating that analogous to cyclins D1 and D2, cyclin D3 is essential for timely progression through G1. In contrast to cyclins D1 and D2, cyclin D3 was (i) ubiquitously expressed among a panel of 70 human cultured cell types; (ii) strongly upregulated upon induction of HL-60 leukaemia cells to differentiate; and (iii) accumulated to high levels in a wide range of quiescent cell types in mouse and human differentiated tissues. Complementary analyses of human biopsies and mouse tissues at different stages of foetal and postnatal development revealed lineage-dependent transient or long-term accumulation of the cyclin D3 protein, correlating with initiation/establishment or maintenance of the mature phenotypes, respectively. Our data support the notion that the biological roles of the individual D-type cyclins are not fully redundant, and suggest a possible dual role for cyclin D3 in cell proliferation and induction and/or maintenance of terminal differentiation.

Differential patterns of cell cycle regulatory proteins expression in transgenic models of thyroid tumours

Cell cycle proteins regulate the transitions from G1 to S and G2 to M phases. In higher eukaryotes, their function is controlled by intracellular cascades regulated by extracellular growth factors. We have studied in previously described transgenic mouse models for thyroid proliferative diseases the expression of the key proteins regulating the cell cycle by Western blotting and immunohistochemistry, and have correlated the observations with the known actions of the transgenes on the signal transduction cascades. In the adenosine A2a receptor model, the cyclic AMP pathway, upstream of the Rb family cell division block, is constitutively activated. In the model expressing HPV 16 E7 protein, the Rb-like proteins are inhibited. Cyclin-dependent kinases cdk4, cdk2 and cdc2, and the associated cyclins D, E and A have been studied. Cyclin D3 appears as the major cyclin D subtype expressed in mouse thyroid epithelial cells in normal and transgenic mice. In the adenosine A2aR model, all cell cycle proteins tested were accumulated. In the E7 model, all cell cycle proteins except for D-type cyclins and cdk4 were also accumulated. A similar pattern was observed in thyroids coexpressing both transgenes, suggesting a dominant effect of E7 over the consequences of the cAMP cascade activation. The cyclin-dependent kinase inhibitors p21cip1/waf1 and p27kip1 were not downregulated in these proliferating thyroids which suggest other roles than the inhibition of the cell cycle progression.

Biochemical findings in the ejaculate of men with non-obstructive azoospermia

In men with non-obstructive azoospermia, testicle biopsy can provide isolated sperm which can be used for fertilization of an oocyte. The male seminal plasma was examined for adequate biochemical parameters and then tested as potential diagnostic parameters for prediction of sperm presence in non-obstructive azoospermia. Sperm was obtained by preparation of the testicular tissue. Biochemical parameters in men with found sperm were compared to findings obtained from men without sperm in the testicular tissue. The following parameters were analysed: fructose, lactate dehydrogenase, total acid phosphatase, Zn, K, Na, Cl, pH. No statistically significant differences were found in both groups under study. Biochemical examination of the ejaculate cannot provide any prediction of sperm retrieval in non-obstructive azoospermia.

Rac and Cdc42 are potent stimulators of E2F-dependent transcription capable of promoting retinoblastoma susceptibility gene product hyperphosphorylation

The Rho family of GTPases plays an important and diverse role in reorganization of the actin cytoskeleton, transcriptional regulation, and multiple aspects of cell growth. Our study has examined their potential links to the cell cycle machinery. We find that constitutively active mutants of Rac and Cdc42, but not Rho, are potent inducers of E2F transcriptional activity in NIH 3T3 fibroblasts. Furthermore, activated Rac and Cdc42, but again not Rho, are capable of inducing cyclin D1 accumulation and pRB hyperphosphorylation in serum-deprived cells, outlining one route leading to enhanced E2F-mediated transcription. The inhibitory effect of the cyclin-dependent kinase inhibitors, p16(ink4), p21(cip1), and p27(cip) on Rac/Cdc42-mediated E2F transcription corroborates a role for pRB family members and their functional inactivation by cyclin-dependent kinases in generating E2F activity. While the up-regulation of E2F transcriptional activity by Rac or Cdc42, not Rho, suffices for entry into S phase and DNA synthesis in Rat-1 R12 cells, this is clearly not the case in NIH 3T3, where additional requirements must exist.

[Determination of cardiac troponin-I in prediction of thrombolysis]

Acute myocardial infarction (AMI) is a disease with high morbidity and mortality. Diagnosis of AMI using common methods (classical biochemistry, ECG) fails even in the fifth part of patients so that other noninvasive diagnostic methods are preferred. Recently, the biochemical analysis has been restored in the case of AMI diagnostics and also in prediction of coronary reperfusion after administration of a fibrinolytic agent. A suitable markers of AMI diagnostics is a combination of myoglobin and cardial troponin-I which is reported as a marker with high specificity and sensitivity. To determine coronary reperfusion, the examination of cardial troponin-T and CK-MB mass is recommended. In the literature, there exist isolated papers dealing with dynamics of cTn-I suitable for prediction of coronary revascularization. However, these papers do not report any adequate algorithm and subsequently mathematical differences between successful thrombolysis and failing thrombolysis. Therefore the aim of our study was to describe dynamics of cTn-I changes in AMI patients treated by thrombolysis. The study comprised of 8 AMI patients with delay from the occurrence of pains to fibrinolysis application under 4 hours (delay 4 hrs). These probands were examined for concentration of cTn-I and CK-MB mass in 3-hour intervals in the first 48 hours after admission to the clinic and further in 6-hour intervals from the hour 48 to the hour 90 after admission. All probands had a successful reperfusion (estimated using CK-MB peak, in 4 patients reperfusion was verified by subsequent coronarography). However, a simple mathematical prediction of coronary reperfusion after acute myocardial infarction by means of cTn-I dynamics determination is not possible due to relatively low cTn-I differences in individual analyses (CK-MB mass analysis shows more significant differences). Thus, in order to determine coronary revascularization, we recommend to use common analyses of dynamics of cTn-T or CK-MB mass.

Synthesis of a neoglycoprotein containing the Lewis X analogous trisaccharide beta-D-GalpNAc-(1-->4)[alpha-L-Fucp-(1-->3)]-beta-D-GlcpNAc

The trisaccharide allyl glycoside 36 and related disaccharide part structures have been prepared using the 2-trichloroacetamido-2-deoxy-alpha-D-galactopyranosyl trichloroacetimidate derivative 9 as glycosyl donor under promotion with TMSOTf or Sn(OTf)2, respectively, to produce the beta-(1-->4) linkage to suitably protected glucosamine derivatives in fair yields. Fucosylation was effected employing the ethyl 1-thio glycosyl donor 20 in the presence of IDCP. Deprotection of the intermediates afforded the disaccharide allyl glycosides beta-D-GalpNAc-(1-->4)- beta-D-GlcpNAc 13, beta-D-GalpNClAc-(1-->4)-beta-D-GlcpNAc 14, alpha-L-Fucp-(1-->3)-beta-D-GlcpNAc 24, alpha-L-Fucp-(1-->4)-beta-D- GlcpNAc 31 and the branched trisaccharide allyl glycoside beta-D-GalpNAc-(1-->4)[alpha-L-Fucp-(1-->3)]-beta-D-GlcpNAc 36. The trisaccharide which corresponds to a structural motif occurring in N-glycoprotein glycans from human urokinase, human recombinant protein C, phospholipase A2 as well as O-glycans, was converted into a neoglycoprotein following introduction of a cysteamine-derived spacer group and subsequent activation with thiophosgene.

[Leptin, insulin and proinsulin--their relationship]

Leptin is protein produced by mature adipocytes into the system circulation and gives information to hypothalamic centers about fat amount in the organism. Leptin is supposed to play a causal role in energy output of the organism and influences the appetite (antiobese effect). Obese individuals were proved to have frequently hyperleptinemia. This disease is caused by a postreceptor disorder (however, several obese families had also normoleptinemia or even hypoleptinemia which is caused by polymorphism of Ob-gene). It was also found that leptin administration in animals leads to reduced appetite and decreased body weight. Interpretation of leptinemia in human is very complicated because leptinemia is influenced by many independent regulations (hormones, stress, food intake, motor activity atc.). Obesity is often associated with hyperinsulinemia and insulin resistance (a frequent cause of human mortality) so that correlations between insulin and leptin are intensively studied. Experimental models and animal studies revealed the existence of adipoinsular axis and it was found that insulin and leptin are contrahormones. In human studies, the majority of authors did not find correlation between leptinemia and markers of insulin secretion. Similar conclusions were drawn out in our previous paper [118]. This may be due to complex regulations of leptinemia in the organism and the use of biochemical markers with limited validity (insulin, C-peptide in fasting state and after stimulation). Therefore we decided to study correlation between leptinemia and intact proinsulin in the serum which is now considered to be the most valid marker of insulin secretion and provides information about an average "daily" insulinemia. This study was stimulated by the fact that increased leptinemia is found also in persons with prolonged hyperinsulinemia (a short-term hyperinsulinemia does not affect leptin concentration so that no available marker of insulin secretion is valid). We examined the group of 31 probands, patients of the Metabolic and Diabetologic Center at the hospital in Sternberk. They were diabetic patients of type 2 who were treated by peroral antidiabetics and insulin and who met criteria of good compensation. However, no correlation between leptinemia and proinsulinemia was found. We suppose that this failure was due to complicated fine regulations affecting leptinemia and also to the fact that intact proinsulin is not an "ideal" marker of a long-term hyperinsulinemia (correlation between insulin and leptin at euglycemic clamp indicates that there exist correlation between these parameters in human).

Aberrations of the G1- and G1/S-regulating genes in human cancer

Deregulated cell proliferation is the hallmark of cancer, and convergent data from the fields of cell-cycle research and molecular oncology have revealed the key role played by abnormalities of the cell-cycle control genes in multistep tumorigenesis. Along with the p53-mediated DNA damage checkpoint, the G1-governing pathway of D-type cyclins, their partner cyclin-dependent kinases (Cdk), Cdk inhibitors, and the retinoblastoma protein constitute a functional unit and prominent oncogenic target. We have learned a great deal about the molecular basis of G1 phase progression and G1/S transition, their proto-oncogenic defects, and potential clinical significance including diagnostic and prognostic applications and new approaches to gene therapy of cancer.

A requirement for cyclin D3-cyclin-dependent kinase (cdk)-4 assembly in the cyclic adenosine monophosphate-dependent proliferation of thyrocytes

In different systems, cyclic adenosine monophosphate (cAMP) either blocks or promotes cell cycle progression in mid to late G1 phase. Dog thyroid epithelial cells in primary culture constitute a model of positive control of DNA synthesis initiation and G0-S prereplicative phase progression by cAMP as a second messenger for thyrotropin (TSH). The cAMP-dependent mitogenic pathway is unique as it is independent of mitogen-activated protein kinase activation and differs from growth factor-dependent pathways at the level of the expression of several protooncogenes/transcription factors. This study examined the involvement of D-type G1 cyclins and their associated cyclin-dependent kinase (cdk4) in the cAMP-dependent G1 phase progression of dog thyroid cells. Unlike epidermal growth factor (EGF)+serum and other cAMP-independent mitogens, TSH did not induce the accumulation of cyclins D1 and D2 and partially inhibited the basal expression of the most abundant cyclin D3. However, TSH stimulation enhanced the nuclear detection of cyclin D3. This effect correlated with G1 and S phase progression. It was found to reflect both the unmasking of an epitope of cyclin D3 close to its domain of interaction with cdk4, and the nuclear translocation of cyclin D3. TSH and EGF+serum also induced a previously undescribed nuclear translocation of cdk4, the assembly of precipitable cyclin D3-cdk4 complexes, and the Rb kinase activity of these complexes. Previously, cdk4 activity was found to be required in the cAMP-dependent mitogenic pathway of dog thyrocytes, as in growth factor pathways. Here, microinjections of a cyclin D3 antibody showed that cyclin D3 is essential in the TSH/ cAMP-dependent mitogenesis, but not in the pathway of growth factors that induce cyclins D1 and D2. The present study (a) provides the first example in a normal cell of a stimulation of G1 phase progression occurring independently of an enhanced accumulation of cyclins D, (b) identifies the activation of cyclin D3 and cdk4 through their enhanced assembly and/or nuclear translocation, as first convergence steps of the parallel cAMP-dependent and growth factor mitogenic pathways, and (c) strongly suggests that this new mechanism is essential in the cAMP-dependent mitogenesis, which provides the first direct demonstration of the requirement for cyclin D3 in a G1 phase progression.

C-ANCA and p-ANCA in patients with Crohn's disease

In 32 patients suffering from various stages of activity of Crohn's disease, c-ANCA and p-ANCA in serum were examined. Altogether, 54 blood samples were examined. In 21 patients of 32, i.e. 65.6%, at least in one examination of c-ANCA in serum the value was higher than 9 units (positive finding). In 10 patients of 32, i.e. 32.2%, at least in one examination of p-ANCA in serum the value was higher than 9 units (positive finding). In the case of high activity of Crohn's disease, c-ANCA in serum were higher than 9 units (positive finding) in 69.6% examinations, in case of low activity, values of c-ANCA in serum were higher than 9 units (positive finding) only in 9.5% examinations. p-ANCA in serum were, when the activity was high, positive in 46.1% examinations, while when the activity of Crohn's disease was low, p-ANCA were positive in 9.5%. The question of specificity of findings is discussed.

The level of neopterin in blood serum as one of the possible prognostic markers of Crohn's disease activity

Neopterine is considered to be one of the markers of immunity system activity. An increased level of this pteridine derivate is determined in blood or urine in infections, transplant rejections, and in other conditions accompanied by changes in the immunity system. Monitoring its level in various body liquids can be important when assessing the immunity system condition, nevertheless, its non-specificity causes difficulties when interpreting the results. Up to now, very few papers have been published dealing with the determination of neopterine levels in patients with IBD. We studied a group of 25 patients who are monitored in a longterm manner at our clinic suffering from Crohn's disease. During 1993 and 1994, we were determining their levels of neopterine in blood together with other parameters. It was a group of patients chosen at random in different stages of disease, and we were interested in the correlation of the height of neopterine level with the activity of Crohn's disease. We proved statistically unimportant correlation between the height of neopterine level in blood serum and Crohn's disease activity. The question is discussed whether the examination of this marker be useful when monitoring Crohn's disease activities.

The retinoblastoma protein pathway in cell cycle control and cancer

Recent discoveries in diverse fields of biomedical research have merged to reveal the molecular basis of cell cycle control and a critical role of subverting this homeostatic mechanism in cancer development. At the heart of these processes lies a late G1 checkpoint governed by the "RB pathway" whose molecular composition, functions, and cancer-associated defects are briefly evaluated in this review. This exciting new knowledge raises a plethora of conceptual issues in cell biology, with potential practical implications for biotechnology and medicine.

[p16 and p53 genes transferred with the help of adenovirus to induce apoptic tumor cell death]

Based on studies of the cell cycle in tissue cultures of cancer cell lines and cells from normal tissue interference in the regulatory network of pRB/cdk4/cyclin D1/p16 in combination with the tumour suppressor gene p53 was investigated. It was shown that overexpression of p53 and p16, but not p53 on its own, induced apoptotic cell death only in tumour cells. Gene transfer of the same two genes to tumours transplanted subcutaneously in mice also caused fast regression of some of the tumours.

Cyclin D1 expression in mantle cell lymphoma is accompanied by downregulation of cyclin D3 and is not related to the proliferative activity

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

p53 protein in endometrial cancer is related to proliferative activity and prognosis but not to expression of p21 protein

Expression of the tumor suppressor gene product p53 and the cyclin-dependent kinase inhibitor p21, which is transcriptionally activated by p53, was investigated and compared with patient survival in a retrospective longitudinal study of 202 cases of endometrial carcinoma. The median duration of follow-up was 4.3 years. P53 was observed immunohistochemically in 63 (31%) of the tumors and was found by univariate analysis to be related to reduced adjusted survival (p = 0.00028) and disease-free survival (p = 0.04). However, p53 expression was not found by multivariate analysis to be an independent prognostic factor when compared with FIGO stage, histologic grade, and proliferative activity, as determined by immunoreactivity for topoisomerase IIalpha with the antibody Ki-S1. Overexpression of p53 was related to histologic grade (p < 0.00001), proliferative activity (p = 0.0071), and inversely to progesterone receptor content (p = 0.042). Immunohistochemical identification of p21 was investigated in 95 cases and found to be positive in 19 (39%) of 49 tumors with p53 overexpression and in 13 (28%) of 46 tumors without p53 overexpression (p = 0.28). Expression of p21 is therefore not related to p53 expression, nor was it found to be related to proliferative activity. Strong expression of p21 was observed in tumors negative for progesterone receptors (p = 0.0028). P53 in endometrial carcinoma is not associated with induction of the cell cycle inhibitor p21, but is associated with an enhanced proliferative activity. The findings of multivariate analysis suggest that the prognostic significance of p53 is related mainly to cell proliferation.

Induction of S-phase entry by E2F transcription factors depends on their nuclear localization

The E2F transcription factors are essential for regulating the correct timing of activation of several genes whose products are implicated in cell proliferation and DNA replication. The E2Fs are targets for negative regulation by the retinoblastoma protein family, which includes pRB, p107, and p130, and they are in a pathway that is frequently found altered in human cancers. There are five members of the E2F family, and they can be divided into two functional subgroups. Whereas, upon overexpression, E2F-1, -2, and -3 induce S phase in quiescent fibroblasts and override G1 arrests mediated by the p16INK4A tumor suppressor protein or neutralizing antibodies to cyclin D1, E2F-4 and -5 do not. Using E2F-1 and E2F-4 as representatives of the two subgroups, we showed here, by constructing a set of chimeric proteins, that the amino terminus of E2F-1 is sufficient to confer S-phase-inducing potential as well as the ability to efficiently transactivate an E2F-responsive promoter to E2F-4. We found that the E2F-1 amino terminus directs chimeric proteins to the nucleus. Surprisingly, a short nuclear localization signal derived from simian virus 40 large T antigen could perfectly substitute for the presence of the E2F-1 amino terminus in these assays. Thus, nuclearly localized E2F-4, when overexpressed, displayed biological activities similar to those of E2F-1. Furthermore, we showed that nuclear localization of endogenous E2F-4 is cell cycle regulated, with E2F-4 being nuclear in the G0 and early G1 phases and mainly cytoplasmic after the pRB family members have become phosphorylated. We propose a novel mechanism for the regulation of E2F-dependent transcription in which E2F-4 regulates transcription only from G0 until mid- to late G1 phase whereas E2F-1 is active in late G1 and S phases, until it is inactivated by cyclin A-dependent kinase in late S phase.

[Leptin in persons with simple obesity]

Obesity is a disease with distinct genetic determination and its phenotype is defined by the still unknown number of genes whose expression can be influenced by environmental factors. Several years ago, "obesity gene" was isolated in animals. This gene, coding protein which consists of 165 amino acids, is called leptin. Leptin is supposed to be a key substance controlling homeostasis of body weight and energy balance; it is produced by adipocytes and its value correlates highly significantly with anthropometric parameters that characterize physical constitution and amount of subcutaneous fatty tissue. The obese individuals often display hyperleptinemia which is frequently caused by a postreceptor disorder; sporadically, a different leptin structure or hypoleptinemia (caused by genetic anomaly) are reported. It is supposed that either absolute or relative leptin deficiency in obese persons are associated with causal obesity (e.g. appetite stimulation). Leptinemia values correlate with percentage of subcutaneous fatty tissue, insulinemia and sometimes with glycemia. In our study we examined 200 probands, patients of the Metabolic and Diabetologic Out-Patient Department, Hospital in Sternberk. A very close correlation between the amount of subcutaneous fatty tissue (measured by a caliper in 10 skinfolds) and the leptine serum concentration was found. The values of leptinemia in men of normal constitution ranged within 1-11 ng/ml, non-obese women had 3-4 times higher values. Leptinemia in some obese individuals reached up to 70 ng/ml. However, the currently calculated and reported parameters of physical constitution (BMI, WHR, Grant index) did not correlate significantly with leptinemia. Similarly, biochemical parameters considered as general markers of insulin resistance (often associated with obesity) did not correlate significantly with leptinemia. This finding indicates that some calculated parameters, quantifying and gualifying physical constitution, may be ambiguous and leptinemia was found to give more detailed information about the amount of subcutaneous fatty tissue than WHR or BMI. An accidental finding was an important positive correlation between myoglobin concentration and creatinemia. At monitoring the effect of hypolipidemic agents we use the myoglobin examination and therefore we consider this correlation to be very important and every physician performing this analysis should be informed about it. The present study thus confirmed that a more accurate quantification of subcutaneous fatty tissue is required. On the other hand, we believe that examination of leptinemia can contribute significantly to stratification of patients into risk groups (with respect to clinical, economic and time differentiation) and subsequently to the treatment of these patients. In future, criteria for quantification of leptinemia and leptine resistance should be defined precisely.

Aberrant p21(CIP1/WAF1) protein accumulation in head-and-neck cancer

p21(CIP1/WAF1) is an inhibitor of cyclin-dependent kinases and, in normal tissues including squamous epithelia, has been associated with cell-cycle exit and differentiation. As shown in this pilot study, however, the majority of head-and-neck squamous-cell carcinomas (HNSCC) display aberrant p21(CIP1/WAF1) expression: of 42 tumors analyzed by immunohistochemical staining, 28 (67%) over-expressed the p21(CIP1/WAF1) protein. Accumulation of p21(CIP1/WAF1) was independent of the histological grade of the tumors as well as the genetic status of the p53 gene. In many cases, most notably in poorly differentiated or undifferentiated HNSCC, p21(CIP1/WAF1)-positive cells were actively proliferating tumor cells, since they also expressed proliferating-cell nuclear antigen (PCNA) and Ki-67. Accumulation of p21(CIP1/WAF1) occurred through a post-transcriptional mechanism since, in contrast to immunohistochemical analysis of the p21(CIP1/WAF1) protein, in situ hybridization showed no increase of mRNA levels as compared with cells in normal mucosa (n = 25). Clinically, among the patients with p21(CIP1/WAF1)-over-expressing tumors, there was increased recurring disease (p = 0.03; chi2-test), shortened disease-free survival (p = 0.0019; log-rank test) and shortened overall survival (p = 0.0071; log-rank test). These in vivo data indicate that in many HNSCC, accumulated p21(CIP1/WAF1) is compatible with increased tumor-cell proliferation, and they provide preliminary evidence that p21(CIP1/WAF1) may be of prognostic and predictive significance.

[Magnesium balance in patients with spasmophilia. Relation to results of electromyography]

BACKGROUND

The pathophysiological basis of spasmophilia is frequently magnesium deficiency and the therapeutic administration of magnesium salts has usually a favourable effect. However the parameters of magnesium balance are not always consistent with the results of electromyography. The objective of the present work was to test and interpret the relationship of results of these two basic diagnostic procedures indicated when spasmophilia is suspected.

METHODS AND RESULTS

Thirty-three subjects (9 men and 24 women) with suspected spasmophilia were examined by non-invasive electromyography, using the technique of surface electrodes. All subjects had concurrently biochemical examinations: serum calcium and ionized calcium, serum magnesium (S-mg), magnesium in erythrocytes (ery-Mg) and magnesium in the blood haemolysate (H-Mg). In 29 patients and oral magnesium loading test was made with evaluation of the urinary Mg excretion after a constant Mg load (U-Mg). Statistical evaluation of the investigated parameters of the magnesium balance revealed a highly significant relationship between ery-Mg and U-Mg and H-Mg and ery-Mg (p < 0.005). A less close relationship was found between H-Mg and S-Mg (p < 0.05). Total and ionized calcium was in all examined subjects within the range of the arbitrary normal range. The EMG finding was positive (the finding of two and more multiplets in the ischaemic and hyperventilation test resp.) in 30 instances, i.e. in 91% of the examined subjects. In 72% there was agreement of the positivity of the EMG and magnesium deficiency (i.e. reduced values of ery-Mg and U-Mg), positivity of EMG combined with normal parameters of the Mg balance was recorded in 18%. In 6.1% of the examined subjects magnesium deficiency was confirmed combined with a normal EMG finding.

CONCLUSIONS

Concurrent positivity of EMG and magnesium deficiency in 72% justifies the therapeutic administration of magnesium. In patients with a normal magnesium deficiency and positive EMG another cause of spasmophilia must be taken into consideration, incl. technical errors of interpretation of EMG results. A negative EMG associated with magnesium deficiency can suggest the central form of tetany, where magnesium treatment is also unequivocally indicated.