The protective effects of ischemic and calcitonin gene-related peptide-induced preconditioning on myocardial injury by endothelin-1 in the isolated perfused rat heart

This study was to investigate the effects of ischemic preconditioning on endothelin-1-induced myocardial injury and the role of calcitonin gene-related peptide (CGRP) played in such effects. The rat hearts were perfused in a Langendorff mode. Heart rates (HR), coronary flow (CF), left ventricular pressure (LVP) and its first derivative (LV dp/dtmax) were recorded and creatinine phosphate kinase (CPK) from coronary effluent was measured. There were no changes in HR, CF, LVP, or LV dp/dtmax throughout the experiment in the control hearts. Endothelin-1 (100 pmol) significantly decreased HR and CF, impaired the cardiac function, and increased the CPK release. However, the HR, CF, LVP and LV dp/dtmax were significantly improved, while the CPK release was decreased in the preconditioned hearts. CGRP8-37, a selective CGRP receptor antagonist, abolished the cardioprotection of ischemic preconditioning, such as the cardiac function and the CPK release. A similar cardioprotection was observed in the hearts pretreated with CGRP. However, the CGRP-induced preconditioning-like protection was abolished in the presence of CGRP8-17 or 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine, an inhibitor of protein kinase C. The present study suggests that the cardioprotective effect of ischemic preconditioning on endothelin-1-induced myocardial injury is mediated by CGRP, and that the cardioprotection of CGRP-induced preconditioning is related to the activation of protein kinase C.

[Kidney reinforcing and yang supporting action of cistanche deserticola Y. C. Ma before and after preparation]

The weights of seminal vesicle and prostate gland of castrated young rats were significantly increased by administration of alcoholsoluble extract from decoction of Cistanche deserticola. The weights of testes, seminal vesicle and prostate gland in mice and rats were also increased by the extract. The phagocytic function of intra-abdominal macrophage in mice was activated by decoction of Cistanche deserticola. The results showed no statistical differences between crude and prepared drugs. The maximum oral tolerance for mouse was 40 g/kg.

Purification and crystallization of cyclin-dependent kinase inhibitor p21

p21, a universal inhibitor of mammalian cyclin-dependent kinases (CDK), regulates cell cycle progression by forming various distinct protein complexes with cyclins, CDKs, and the proliferating cell nuclear antigen. We have overexpressed recombinant human p21 in E. coli and purified active p21 to near homogeneity on a large scale. Crystals of recombinant p21 have been grown in the space group P2(1) a = 157.4, b = 152.7, c = 90.6 A, and beta = 92.7 degrees. The diffraction data of the recombinant p21 have been collected to 2.5 and 3.5 A resolution for the native crystal and two heavy atom derivatives of mercury and iridium.

A role for a p21-E2F interaction during senescence arrest of normal human fibroblasts

The family of E2F transcription factors forms different multiprotein complexes with cell cycle regulatory proteins to control the expression of genes important in cell proliferation. In this study, we identified four distinct E2F complexes present in aged and senescent normal, human diploid fibroblasts. Two appeared to be identical to the previously described G1-specific p130 and Rb-E2F complexes present in young G0-arrested cells. The other two were novel E2F complexes that contained the cyclin-dependent kinase inhibitor p21 (cip1/WAF1/Sdi1/CAP20/PIC1) complexed with Rb/CDK2/cyclin E or with the Rb-related p107/CDK2/ cyclin D. These p21-E2F complexes, while present in young G1 cells at very low levels, were elevated in senescent cells. The p21 containing E2F complexes were not detected during the S-phase in young cells. The DNA-binding stability of the p21 complexes was approximately 10 times greater than the stability of any other E2F complex or uncomplexed E2F. Addition of purified p21 protein to the S-phase-specific cyclin A/ CDK2-p107-E2F complex from young cells dissociated cyclin A and CDK2 from p107/E2F, suggesting an additional novel function for p21. Finally, expression of p21 specifically inhibited transcription from an E2F-dependent promoter but had no effect on a mutant E2 promoter. In addition to its inhibition of CDK enzymes and proliferating cell nuclear antigen function in DNA replication, these studies reveal a novel mechanism by which p21 mediates growth arrest: direct interaction with E2F complexes and negative regulation of E2F transcription factor activity.

Thapsigargin induces rapid, transient growth inhibition and c-fos expression followed by sustained growth stimulation in mouse keratinocyte cultures

Although the sesquiterpene lactone thapsigargin has been shown to possess hyperplastic and tumor-promoting activities when applied topically to mouse skin in vivo, the cellular mechanism(s) which underlie these effects are unclear. We show here that thapsigargin treatment of Primary mouse epidermal keratinocytes increased intracellular free Ca2+ concentration (Cai) in a concentration-dependent manner. Thapsigargin induced a rapid, transient elevation in keratinocyte Cai, in part due to the release of Ca2+ from intracellular stores. This response was followed by a sustained elevation in Ca2+, resulting entirely from calcium influx. Thapsigargin elicited a biphasic effect on keratinocyte DNA synthesis: a rapid inhibitory effect (50-60% inhibition at 4-8 h), followed by a very marked and sustained elevation. Prolonged treatment of keratinocytes with thapsigargin at relatively high concentrations resulted in cytotoxicity (inhibition of neutral red uptake). The rapid antiproliferative effect of thapsigargin was not associated with cytotoxicity, as determined by either neutral red uptake or by trypan blue exclusion, and was not blocked by pretreatment with Ro 31-7349, a selective inhibitor of protein kinase C. The rapid antiproliferative effect of thapsigargin was associated with rapid, transient activation of keratinocyte c-fos expression and rapid inhibition of total protein synthesis. Taken together, these findings raise the possibility that the hyperplastic and tumor-promoting activities of thapsigargin on epidermis in vivo result from direct keratinocyte growth stimulation as a consequence of a prolonged elevation in levels of Cai.

Lipid peroxidation of mitochondrial membrane induced by D1: an organic solvent extractable component isolated from a crude extract of burn eschar

D1, an organic solvent extractable component of an extract from burn eschar was characterized and the mechanism of its inhibitory effect on mitochondrial respiratory functions was investigated. Using silicic acid column chromatography, it was found that D1 consisted of two parts: a toxic simple lipid and a non-toxic complex lipid. Six subunits were obtained by further silicic acid column chromatography, among them, the no. 4 and no. 6 were toxic. Infrared spectrometric studies showed that no. 4 consisted of esters, while no. 6 were peroxides. D1 also contained large amounts of malonaldehyde (MDA) and lipid hydroperoxides (ROOH). Vitamin E was found to prevent the inhibitory action of D1 on mitochondrial function and to reduce the amount of MDA produced. However, if vitamin E was introduced after the addition of D1 the inhibition could not be prevented, although there was still a reduction in MDA production; therefore, MDA per se was probably not the cause of the inhibition. D1 induced ROOH formation in mitochondrial membranes. Cumene hydroperoxide, an organic hydroperoxide, was capable of inhibiting the mitochondrial function. This inhibitor action was blocked by vitamin E. It is speculated that ROOH in D1 is probably the element that inhibits mitochondrial function. That D1 caused lipid peroxidation of membrane lipid was also proved by analysing the fatty acid composition of mitochondrial membranes before and after treatment with D1. It was found that the amount of polyunsaturated fatty acids decreased and that of saturated fatty acids increased after incubation with D1, a direct proof that lipid peroxidation has occurred. Lipid peroxidation of the membrane lipid was the result of the action of oxygen free radicals. This process was best shown by a chemiluminescence study. In this experiment, D1 induced chemiluminescence which was dose-dependently related to the amount of D1 used. This was probably the most direct proof that D1 caused lipid peroxidation of membrane lipid resulting in damage of the mitochondria.

[Restriction fragment length polymorphism assays of clinical isolated human cytomegalovirus strain genomic DNA]

Ten clinical isolated strains of Human cytomegalovirus (HCMV) were obtained from 73 urine specimens of different people. Isolations from urine were carried out in human embryolung fibroblasts. Viral isolates were passaged four times. HCMV DNAs of laboratory strain AD169 and 10 clinical isolated strains were extracted with Hirt method, digested with each of the restriction enzymes EcoRI, Hind II. Comparison of restriction fragment length polymorphism (RFLP) of AD169 and isolated strains were made by hybridizing digested DNA with 32P labeled with HCMV Hind II cloned subgenomic fragments as the probe (pCM1035, pCM1015). pCM1035 is located in the joining region between the long(L) and short (S) unique sequences of the virus (L-S junction) pCM1015 is located in the terminal sequences of the virus. The results showed the genomic high degree of homology existed among all strains and the variable restriction site was in the L-S junction and terminal portion. The RFLP patterns of the clinical isolates which did not have relation in epidemiology were different, but the patterns of clinical isolates related in epidemiology were quite similar. Polymorphism frequently occurred in this case of EcoRI digested fragment hybridized with the probe of pCM1035. Southern hybridization of HCMV isolations is useful to researches into the molecular epidemiology and pathogenesis of HCMV infection.

Intragenic mutations of the p16(INK4), p15(INK4B) and p18 genes in primary non-small-cell lung cancers

The p15(INK4B), p16(INK4) and p18 genes are members of the gene family coding for inhibitors of cyclin-dependent kinases 4 and 6. p15(INK4B) and p16(INK4) are located at 9p21, a chromosomal region frequently deleted in many human neoplasms. To examine the role of these 3 genes in lung carcinogenesis, somatic mutations within the genes were analyzed by single-strand conformation polymorphism and DNA sequencing in 71 non-small-cell lung cancer (NSCLC) samples. Six somatic mutations in the p16(INK4) gene and 3 cases with a polymorphic allele were observed. Loss of heterozygosity in the p18 gene was found in 1 sample. We did not find any intragenic mutations in the p15(INK4B) or p18 genes. We conclude that p16(INK4) mutations play a role in the formation of some NSCLCs, whereas the involvement of p15(INK4B) and p18 is uncommon.

[Immunohistochemical detection of antigen of human cytomegalovirus in hepatocyte]

The expression plasmid of human cytomegalovirus (HCMV) 52kd glycoprotein was induced and amplified, and the recombinant protein was extracted. The rabbit antiserum to the recombinant protein was prepared. The antiserum-reacted to the antigen of HCMV AD165, and the titer of antiserum was 1 : 3200 by using 125I-Protein A. Using Avidin-Biotinperoxidase complex technique (ABC method), we detected the HCMV 52 kd glycoprotein in the hapatic slides of 9 cases. Among them, one case (an infant died of congenital heart disease) was held as a negative control. The other 8 cases (patients with clinically diagnosed cytomegalic inclusion disease) had viral hepatitis histopathologically. Of these 8 cases, 7 had positive signals but found in the nucleus and cytomembrane of the hepatocytes, no positive signal was found in the hepatocytes of the control. The result showed that HCMV 52kd glycoprotein was located in the nucleus and on the membrane of the infected hepatocyte. The antibody prepared with the antigen of gene engineering could find the virus antigen and represent the virus gene state which was active or silent. ABC method is not only simple, sensitive and specific, but also effective in localization. It is of importance to clinical diagnosis, differential diagnosis and prognostication.

Endogenous inhibitors of nitric oxide synthesis and lipid peroxidation in hyperlipidemic rabbits

AIM

To examine whether the elevation of endogenous NG, NG-dimethylarginine (DMA) content is related to lipid peroxidation in the high lipid-fed rabbit.

METHODS

In high lipid diet-fed rabbits, concentrations of serum cholesterol, triglyceride, malondialdehyde (MDA), and DMA were measured, and endothelium-dependent relaxation to acetylcholine (ACh) was tested.

RESULTS

After 6-wk on a high lipid-diet, the levels of serum total cholesterol, triglyceride, MDA, and DMA were increased vs those in control group (MDA was 2.88 +/- s 0.20 vs 1.54 +/- 0.13 nmol.L-1, P < 0.01 and DMA was 1.51 +/- 0.07 vs 0.75 +/- 0.13 mumol.L-1, P < 0.01), while the endothelium-dependent vasodilation in the isolated thoracic aorta was impaired (the maximal response to ACh was 45.59 +/- 3.10 vs 76.93 +/- 5.68%). Supplementation with vitamin E decreased MDA and DMA content and improved the endothelium-dependent vasodilation.

CONCLUSIONS

An increase in serum concentration of DMA may be secondary to the elevation of lipid peroxides in the hyperlipidemic rabbit.

Alteration of cell cycle kinase complexes in human papillomavirus E6- and E7-expressing fibroblasts precedes neoplastic transformation

Expression of viral oncoproteins results in the loss of cell cycle checkpoint control and the accumulation of chromosomal abnormalities. Expression of both human papillomavirus type 16 oncoproteins, E6 and E7, in normal human fibroblasts completely dissociates p21 and proliferating cell nuclear antigen from the quarternary cyclin-cyclin-dependent kinase (CDK) complexes present in normal cells, causes disruption of the cyclin D-CDK4 complex and replacement with a CDK4-p16 complex, and leaves binary complexes of cyclin B1-CDC2 and cyclin A-CDK2 intact. These results are identical to those observed in fully transformed cells. The expression of the individual oncoproteins dramatically affects the association of proliferating cell nuclear antigen into the complexes while leaving the total cellular levels unaltered. Expression of low-risk human papillomavirus has no effect on cyclin complexes. These findings provide evidence for the gross alteration of cyclin-CDK complexes in preneoplastic cells and links this alteration to the loss of genomic stability.

Targeted in vivo expression of the cyclin-dependent kinase inhibitor p21 halts hepatocyte cell-cycle progression, postnatal liver development and regeneration

The CDK inhibitor p21 (WAF-1/CIP-1/SDI-1) has been implicated in DNA damage-induced p53-mediated G1 arrest, as well as in physiological processes, such as cell differentiation and senescence, that do not involve p53 function. To determine the impact of p21 on normal development and cell-cycle regulation in vivo, we have generated transgenic mice that abundantly express p21 specifically in hepatocytes. During postnatal liver development, when transgenic p-21 protein becomes detectable, hepatocyte proliferation is inhibited dramatically. This disturbance causes a reduction in the overall number of adult hepatocytes, resulting in aberrant tissue organization, runted liver and body growth, and increased mortality. The transgenic p21 protein is associated with most, if not all, of the cyclin D1-CDK4 in liver but not significantly with other cyclin/CDK proteins, indicating the importance of cyclin D1-CDK4 function in normal liver development. The appearance of large polyploid nuclei in some hepatocytes indicates that p21 may also cause arrest during the G2 phase of the cell cycle. Significantly, partial hepatectomy failed to stimulate hepatocytes to proliferate in p21 transgenic animals. These results provide the first in vivo evidence that appropriate p21 levels are critical in normal development and further implicate p21 in the control of multiple cell-cycle phases.

P/O ratios reassessed: mitochondrial P/O ratios consistently exceed 1.5 with succinate and 2.5 with NAD-linked substrates

The efficiency of ATP synthesis coupled to cell respiration, commonly referred to as the P/O ratio, has been the subject of extensive studies for more that 50 years. The general conclusion from these studies is that respiring mitochondria can convert external ADP to ATP at a maximal P/O ratio of 3 for NAD-linked substrates and 2 for succinate. However, in recent years the validity of these "integral" values has been questioned on both mechanistic and thermodynamic grounds, and a mechanistic P/O ratio of 2.5 for NAD-linked substrates and 1.5 for succinate have been concluded on the basis of experiments with isolated mitochondria. These values have been widely adopted in the scientific literature, including several recent textbooks. In this paper we report that under optimal conditions with respect to preparation and assay procedures, the P/O ratios obtained with isolated rat liver mitochondria consistently exceed 2.5 with NAD-linked substrates and 1.5 with succinate. These results, although not excluding "nonintegral" P/O ratios due to various energy-dissipating side reactions, warrant caution in accepting the reported lower values and, in general, in referring to mechanistic considerations unless the underlying molecular mechanisms are understood.

Mutational analysis of the p16 family cyclin-dependent kinase inhibitors p15INK4b and p18INK4c in tumor-derived cell lines and primary tumors

The growth suppressing activity of the retinoblastoma suspectibility gene product, pRb, is down regulated by cyclin-dependent kinases 4 and 6 (CDK4 and CDK6) whose kinase activity is negatively regulated by CDK inhibitors of the p16 family. We have examined the genomic status of two recently isolated p16-related CDK inhibitors, p15 and p18, in 15 normal and 73 tumor-derived cell lines established from 23 different tissues, as well as 26 invasive primary breast cancers and 20 acute myelogenous leukemias. p15 was found to be homozygously deleted in 22% of the tumor derived cell lines, but no point mutations were found in either the cultured cells or the two types of primary tumors. With the exception of one breast cancer cell line, no deletions or mutations were found in the p18 gene in either cultured cell lines or primary tumors. These results indicate that mutation of the p18 gene occurs rarely in human tumors. Thus, while they share a very similar biochemical mechanism of inhibiting the kinase activity of CDK4 and CDK6, members of the p16 gene family play different roles in controlling cell proliferation and suppressing tumor growth.

Biochemical characterization of the human cyclin-dependent protein kinase activating kinase. Identification of p35 as a novel regulatory subunit

The activation of cyclin-dependent protein kinases (Cdks) is dependent upon site-specific phosphorylation and dephosphorylation reactions, as well as positive and negative regulatory subunits. The human Cdk-activating protein kinase (Cak1) is itself a Cdc2-related cyclin-dependent protein kinase that associates with cyclin H. The present study utilized specific anti-Cak1 antibodies and immunoaffinity chromatography to identify additional Cak1-associated proteins and potential target substrates. Immunoprecipitation of metabolically labeled human osteosarcoma cells revealed a number of Cak1-associated proteins, including p95, p37 (cyclin H), and a 35-kDa protein that was further characterized herein. Microsequence analysis obtained after limited proteolysis revealed peptide fragments that are similar, but not identical to, human and yeast cyclins, thus identifying p35 as a cyclin-like regulatory subunit. The greatest sequence similarity of human p35 is with Mcs2, a yeast cyclin that is essential for cell cycle progression. Immunoaffinity chromatography performed under nondenaturing conditions afforded the isolation of enzymatically active Cak1 from cell lysates, enabling studies of kinase autophosphorylation and comparative substrate utilization. Immunoaffinity-purified Cak1 phosphorylated monomeric Cdc2 and Cdk2, but not Cdk4; the phosphorylation of both Cdc2 and Cdk2 were increased in the presence of recombinant cyclin A. These studies indicate that the Cak1 catalytic subunit, like Cdc2 and Cdk2, associates with multiple regulatory partners and suggests that subunit composition may be an important determinant of this multifunctional enzyme.

Isolation and characterization of p19INK4d, a p16-related inhibitor specific to CDK6 and CDK4

Cyclin-dependent kinases 4 and 6 are complexed with many small cellular proteins in vivo. We have isolated cDNA sequences, INK4d, encoding a 19-kDa protein that is associated with CDK6 in several hematopoietic cell lines. p19 shares equal similarity and a common ancestor with other identified inhibitors of the p16/INK4 family. p19 interacts with and inhibits the activity of both CDK4 and CDK6 and exhibits no detectable interaction with the other known CDKs. p19 protein is present in both cell nuclei and cytoplasm. The p19 gene has been mapped to chromosome 19p13.2, and the level of its mRNA expression varies widely between different tissues. In contrast to p21 and p27 whose interaction with CDK subunits is dependent on or stimulated by the cyclin subunit, the interaction of p19 and p18 with CDK6 is hindered by the cyclin protein. Binary cyclin D1-p18/p19 or cyclin D1-CDK6 complexes are highly stable and cannot be dissociated by excess amounts of cyclin D1 or p19/p18 proteins, suggesting that p16 inhibitors and D cyclins may interact with CDKs 4 and 6 in a competing or potentially mutually exclusive manner.

Molecular cloning of CDK7-associated human MAT1, a cyclin-dependent kinase-activating kinase (CAK) assembly factor

Mammalian CDK7 is a protein kinase identified as the catalytic subunit of cyclin-dependent kinase (CDK)-activating kinase and as an essential component of the transcription factor TFIIH that is involved in transcription initiation and DNA repair. We have identified in human cells a number of CDK7-associated cellular proteins that appear to fall into two classes based on their relative [35S] metabolic labeling intensity. One class of proteins present in CDK7 immunocomplexes as a minor fraction contains components of the TFIIH transcription complex such as p62 and p89ERCC3, whereas the other fraction contains four polypeptides (p35, p37Cyclin H, p75, and p95) that are stoichiometrically associated with CDK7. Whereas the levels of association of p35, p37Cyclin H, and p75 with CDK7 remain unchanged between density-arrested and proliferating Ewing sarcoma EW-1 cells, the association of p95 with CDK7 was significantly decreased as cells reached confluency. Through a large-scale immunopurification of CDK7 complexes and protein microsequencing, we have isolated a cDNA that encodes p35 and have shown that it is the human homologue of Mat1 that is involved in the assembly of CAK. MAT1 contains a highly conserved C3HC4 motif at its NH2 terminus, a characteristic feature shared among RING finger proteins. The human MAT1 gene expresses a single 1.6-kb transcript, the steady-state level of which, like CDK7 and cyclin H, varies significantly in different cell lines and in different terminally differentiated tissues.

Transforming growth factor beta activates the promoter of cyclin-dependent kinase inhibitor p15INK4B through an Sp1 consensus site

Transforming growth factor beta (TGF-beta) causes growth arrest in the G1 phase in many cell types. One probable pathway for this growth inhibition is through the TGF-beta-mediated up-regulation of the cyclin-dependent kinase (CDK) inhibitor p15INK4B, which specifically inhibits the enzymatic activities of CDK4 and CDK6. An active cyclin D-CDK4/6 complex is required for pRb phosphorylation to allow the cell cycle to progress from G1 to S phase. To study the molecular mechanism of the p15INK4B induction by TGF-beta, we isolated a 780-base pair promoter sequence of the human p15 gene and inserted this fragment upstream of a luciferase reporter gene. When this construct was transiently transfected into HaCaT cells, luciferase activity was induced more than 10-fold upon TGF-beta treatment, indicating that the induction of p15INK4B expression by TGF-beta is partly exerted at the transcription level. Promoter deletion analysis revealed that the sequence from -110 to -40 relative to the transcription start site is capable of conferring the 10-fold induction by TGF-beta. Within this region there are three Sp1 consensus sites. Mutation of one of these sites, GGGGCGGAG, substantially reduced both the induction by TGF-beta and the basal promoter activity, whereas mutations in the other two Sp1 sites and the spacer sequences had little effect. In addition, gel mobility shift assay indicates that the transcription factors Sp1 and Sp3 bind to this Sp1 site. Taken together, these data suggest that a specific Sp1 consensus site is involved in the mediation of TGF-beta induction as well as the basal promoter activity of the p15 gene and that Sp1 and Sp3 transcription factors might be involved in this regulation.

Deletion of cyclin-dependent kinase 4 inhibitor genes P15 and P16 in non-Hodgkin's lymphoma

B-cell non-Hodgkin's lymphoma (NHL) is a heterogeneous lymphoid malignancy consisting of several histologic types. Alterations in proto-oncogenes caused by reciprocal chromosome translocations have been implicated in the etiology of specific histologic groups. In this study, we examined the contribution of the cell cycle inhibitor genes P15, P16, and P18 to pathogenesis in a large panel of 209 cytogenetically characterized B-cell NHL tumors representing varied histologic groups. We identified the homozygous deletion of P15 and P16 genes in 13 tumors from 12 patients, all belonging to diffuse large-cell histology; 10 had this diagnosis made on presentation, 1 had transformed from small lymphocytic lymphoma, and 1 had transformed from Hodgkin's disease. Tumor-specific point mutations were not identified in the coding regions of these genes. Cytogenetically, chromosome 9p was normal in all but one tumor. On the other hand, eight tumors hemizygous for 9p by cytogenetic analysis showed wild-type configuration of these genes. Our study, therefore, indicates that deletion of P15 and P16 occurs in about 15% of diffuse large-cell NHL and is not usually detected by cytogenetic analysis. P18 was wild-type in all tumors including the 13 tumors hemizygous for 1p.

[Genes and the modulation of learning and memory]

Recently, progress in the study of the relationship between gene and the modulation of learning and memory was noticeable. The studies showed that: (1) The expression of immediate early genes (IEGs), especially the c-fos, is a necessary prerequisite for the formation of memory; the induction of long term potentiation (LTP) is accompanied by an increase of IEGs expression; (2) Mice with deficiency of alpha-Calcium-Calmodulin Kinase II (alpha-CaMK II), or neural-cell adhesion molecules (N-CAM) or tyrosine kinase gene (fyn) generated by gene targeting appear deficits in spatial learning and memory, mutation of alpha-CaMK II and N-CAM gene can also interfere with the induction and maintenance of LTP; (3) The single-gene mutants of Drosophilia (dnc, rut) showed significant decrease of the ability of memory. The mechanism is related to the altered synaptic plasticity, and the mushroom body may be the memory center of Drosophila.

Both p16 and p21 families of cyclin-dependent kinase (CDK) inhibitors block the phosphorylation of cyclin-dependent kinases by the CDK-activating kinase

Phosphorylation of cyclin-dependent kinases (CDKs) by the CDK-activating kinase is required for the activation of CDK enzymes. Members of two families of CDK inhibitors, p16/p18 and p21/p27, become physically associated with and inhibit the activity of CDKs in response to a variety of growth-modulating signals. Here, we show that the representative members of both families of CDK inhibitors, p21waf1,cip1, p27kip1, and p18, can prevent the phosphorylation of their CDK partners, CDK2 and CDK6, by CDK-activating kinase. No direct interaction between CDK-activating kinase and the CDK inhibitors could be detected, suggesting that binding of these CDK inhibitors to CDK subunits renders CDK inaccessible to the CDK-activating kinase phosphorylation. These findings suggest that a general mechanism of CDK inhibitor function is to block the phosphorylation of CDK enzymes by CDK-activating kinase.

The alternatively spliced type II corticotropin-releasing factor receptor, stably expressed in LLCPK-1 cells, is not well coupled to the G protein(s)

Two alternatively spliced corticotropin-releasing factor receptor (CRF-R) cDNAs, type I and type II, were recently isolated from a human cDNA library. The two cDNAs are identical except that the type II cDNA encodes an additional 29 amino acid inserted in the first putative cytoplasmic loop. Since the first cytoplasmic loop is highly conserved in all the members of the hCRF receptor family we have examined whether the presence of the 29 amino acid cassette in CRF-RII influences G protein coupling in LLCPK-1 cells stably expressing the type I and type II hCRF receptors. Whether measured in intact cells or in membrane preparations, LLCPK-1 cells stably expressing CRF-RII have a 4-5 fold lower binding affinity. Maximal CRF-stimulated cAMP accumulation in LLCPK-1 cells stably expressing CRF-RI was 10-15-fold higher than that in LLCPK-1 cells expressing CRF-RII. The EC50 for CRF-stimulated cAMP accumulation in hCRF-RI-expressing cells was in the range of 0.5 +/- 0.2 nM. In contrast, the EC50 for CRF-stimulated cAMP accumulation in hCRF-RII expressing cells was 7.7 +/- 0.2 nM. hCRF increased phosphoinositide turnover in LLCPK-1 cells stably expressing CRF-RI but not in those expressing CRF-RII; this effect required hCRF concentrations of 100 nM and higher. In membrane preparations, GTP-gamma-S inhibited hCRF binding to CRF-RI and shifted the binding Kd from 4.5 nM to 16.7 nM. Conversely, GTP-gamma-S did not influence hCRF binding to CRF-RII in broken cell membranes. Additionally, CRF-stimulated adenylate cyclase activity in cell membranes expressing CRF-RI was potentiated by GTP, whereas CRF-stimulated adenylate cyclase activity in cell membranes expressing CRF-RII was insensitive to GTP. These data indicate that CRF-RII is not well coupled to the G protein. Since the only difference between the CRF-RII and CRF-RI is the insert in the first putative cytoplasmic loop, these data indicate that the first cytoplasmic loop plays a crucial role in hCRF receptor coupling to the G protein.

Transforming growth factor beta induces the cyclin-dependent kinase inhibitor p21 through a p53-independent mechanism

The transforming growth factor beta s (TGF-beta s) are a group of multifunctional growth factors which inhibit cell cycle progression in many cell types. The TGF-beta-induced cell cycle arrest has been partially attributed to the regulatory effects of TGF-beta on both the levels and the activities of the G1 cyclins and their kinase partners. The activities of these kinases are negatively regulated by a number of small proteins, p21 (WAF1, Cip1), p27Kip1, p16, and p15INK4B, that physically associate with cyclins, cyclin-dependent kinases, or cyclin-Cdk complexes. p21 has been previously shown to be transcriptionally induced by DNA damage through p53 as a mediator. We demonstrate that TGF-beta also causes a rapid transcriptional induction of p21, suggesting that p21 can respond to both intracellular and extracellular signals for cell cycle arrest. In contrast to DNA damage, however, induction of p21 by TGF-beta is not dependent on wild-type p53. The cell line studied in these experiments, HaCaT, contains two mutant alleles of p53, which are unable to activate transcription from the p21 promoter when overexpressed. In addition, TGF-beta and p53 act through distinct elements in the p21 promoter. Taken together, these findings suggest that TGF-beta can induce p21 through a p53-independent pathway. Previous findings have implicated p27Kip1 and p15INK2B as effectors mediating the TGF-beta growth inhibitory effect. These results demonstrate that a single extracellular antiproliferative signal, TGF-beta, can act through multiple signaling pathways to elicit a growth arrest response.

Signaling properties of mouse and human corticotropin-releasing factor (CRF) receptors: decreased coupling efficiency of human type II CRF receptor

CRF is the primary neuroregulator of the function of the hypothalamic-pituitary-adrenal axis. We have recently cloned a mouse CRF receptor (mCRF-R) complementary DNA (cDNA) from an AtT-20 cell cDNA library by polymerase chain reaction. To compare the functions of mCRF-R to those of the human type I and type II CRF receptors (hCRF-RI and hCRF-RII), cDNAs were cloned into the expression vector pcDNA1 and transfected into COS-7 cells. CRF binding and CRF-stimulated cAMP accumulation as well as phosphoinositide hydrolysis were measured. Scatchard analysis of the binding of 125I-labeled [Tyr0]r/hCRF ([125I]CRF) to COS-7 cells expressing mCRF-R and hCRF-RI cDNAs revealed the same apparent Kd (9 nM). In contrast, the apparent binding Kd for hCRF-RII was 20 nM CRF. Maximal stimulatory concentrations (1 microM) of rat/human CRF-(1-41) (r/hCRF) increased cAMP accumulation in COS-7 cells transfected with mCRF-R, hCRF-RI, and hCRF-RII cDNA plasmid (10 micrograms each) from basal values of 8-19 pmol/10(5) cells.15 min to 84 +/- 10, 87 +/- 16, and 45 +/- 16 pmol/10(5) cells.15 min, respectively. The EC50 values of r/hCRF-stimulated cAMP accumulation in COS-7 cells expressing mCRF-R and hCRF-RI cDNAs were similar at 0.4 +/- 0.2 and 0.7 +/- 0.2 nM, respectively. Conversely, the EC50 of r/hCRF-stimulated cAMP accumulation in hCRF-RII-transfected COS-7 cells was 47.5 +/- 18.9 nM. As the level of expression of hCRF-RII was lower than that of hCRF-RI, we compared r/hCRF-stimulated cAMP accumulation in COS-7 cells expressing low and high levels of hCRF-RI. The EC50 for r/hCRF-stimulated cAMP accumulation in COS-7 cells transfected with hCRF-RI did not change when receptor expression was varied by a factor of 1- to 8.4-fold. In contrast, the EC50 for r/hCRF-stimulated cAMP accumulation mediated by hCRF-RII was at least 100-fold higher than that mediated by the hCRF-RI in COS-7 cells, which suggests poor coupling between hCRF-RII and adenylate cyclase. Inositol phosphate (IP) levels were also determined in mCRF-R, hCRF-RI, and hCRF-RII cDNA-transfected COS-7 cells stimulated with increasing concentrations of r/hCRF. r/hCRF-stimulated IPs accumulation was dose dependent in COS-7 cells expressing mCRF-R and hCRF-RI using 100 and 1000 nM r/hCRF. Concentrations of 10 (or less) nM r/hCRF had no effect on IP generation. hCRF-RII did not mediate stimulation of IP even at 1000 nM r/hCRF.(ABSTRACT TRUNCATED AT 400 WORDS)

A novel plasminogen activator from snake venom. Purification, characterization, and molecular cloning

A novel plasminogen activator from Trimeresurus stejnegeri venom (TSV-PA) has been identified and purified to homogeneity. It is a single chain glycoprotein with an apparent molecular weight of 33,000 and an isoelectric point of pH 5.2. It specifically activates plasminogen through an enzymatic reaction. The activation of human native Glu-plasminogen by TSV-PA is due to a single cleavage of the molecule at the peptide bond Arg561-Val562. Purified TSV-PA, which catalyzes the hydrolysis of several tripeptide p-nitroanilide substrates, does not activate nor degrade prothrombin, factor X, or protein C and does not clot fibrinogen nor show fibrino(geno)lytic activity in the absence of plasminogen. The activity of TSV-PA was readily inhibited by phenylmethanesulfonyl fluoride and by p-nitrophenyl-p-guanidinobenzoate. Oligonucleotide primers designed on the basis of the N-terminal and the internal peptide sequences of TSV-PA were used for the amplification of cDNA fragments by polymerase chain reaction. This allowed the cloning of a full-length cDNA encoding TSV-PA from a cDNA library prepared from the venom glands. The deduced complete amino acid sequence of TSV-PA indicates that the mature TSV-PA protein is composed of 234 amino acids and contains a single potential N-glycosylation site at Asn161. The sequence of TSV-PA exhibits a high degree of sequence identity with other snake venom proteases: 66% with the protein C activator from Agkistrodon contortrix contortrix venom, 63% with batroxobin, and 60% with the factor V activator from Russell's viper venom. On the other hand, TSV-PA shows only 21-23% sequence similarity with the catalytic domains of u-PA and t-PA. Furthermore, TSV-PA lacks the sequence site that has been demonstrated to be responsible for the interaction of t-PA (KHRR) and u-PA (RRHR) with plasminogen activator inhibitor type 1.

[The effectiveness of combined insulin and sulfonylurea in treating non-insulin dependent diabetic patients]

The effectiveness of combined therapy with insulin and sulfonylurea in non-insulin dependent diabetes mellitus (NIDDM) patients has, for decades, been a debated issue. In order to probe this question, we studied 33 diabetes mellitus patients aged 40 years and over, having a history of this disease for more than 5 years, treated with one of the sulfonylureas at maximal dosage for three weeks but without effect. These 33 cases were divided into three groups randomly: group A: treated with glurenorm and insulin. B insulin and C glurenorm. The treatment lasted 4 months. During the course of the trial, estimation of the free-insulin, C-peptide, blood glucose etc. was carried out three times i.e. one before the trial and then 2, 4 months after the trial. The data were dealed with U-test and comparison was made before and after the trial and between the three groups. It is shown that combined therapy with sulfonylurea and insulin is effective in NIDDM patients, especially in those with secondary failure of beta-cell function and the combined therapy may be used in NIDDM patients during the transitional period from treatment with sulfonylurea alone to traditional insulin cure.

Role of phosphodiesterase isoenzymes in regulating intracellular cyclic AMP in adenosine-stimulated smooth muscle cells

Three phosphodiesterase (PDE) isoenzymes were separated by Mono Q h.p.l.c. column chromatography from the soluble fraction of a homogenate of pig aortic smooth muscle cells. The first peak of PDE activity was stimulated by calmodulin in the presence of calcium. The second broad peak contained at least two activities, which were sensitive to inhibition by CI-930 or rolipram respectively. The distribution of total cellular enzyme activity in different subcellular fractions was also determined. The majority (78%) of the total activity was present in the cytosolic fraction, 18% of activity was in a membrane-bound form and 4% of activity was associated with the cytoskeleton. Rolipram-sensitive PDE was present predominantly in the cytosolic fraction, whereas cyclic GMP-inhibited, CI-930-sensitive PDE was evenly distributed between the cytosolic and particulate fractions. All of the calmodulin-dependent PDE activity was found in the soluble fraction. CI-930 and rolipram enhanced, by 2-fold and 3-4-fold respectively, the adenosine-stimulated rise in cellular cyclic AMP level. The increase in cyclic AMP levels due to CI-930 or rolipram was dose-dependent. Removal of adenosine once cyclic AMP had risen resulted in a rapid fall in cyclic AMP levels even in the presence of rolipram and CI-930. M&B 22,948, the calmodulin-dependent PDE inhibitor, caused less than a 25% increase of the adenosine-stimulated cyclic AMP levels by itself, but it contributed substantially to controlling the cyclic AMP levels after the removal of adenosine when used together with CI-930 and rolipram. These phenomena suggested that all three PDE isoenzymes participated in modulating cellular cyclic AMP levels after adenosine stimulation, and that differential importance of the individual isoenzymes depends on cellular cyclic AMP levels.

Evidence that diazoxide promotes calcium influx in mouse keratinocyte cultures by membrane hyperpolarization

We have used fura-2/AM to investigate the effect of diazoxide on the cytosolic calcium concentration (Cai) in primary mouse keratinocyte cultures. Treatment of keratinocytes with 100 microM diazoxide induced a transient peak in Cai, followed by a sustained elevation. Depletion of medium calcium by addition of EGTA abolished the diazoxide-induced Cai response, indicating that the agent promoted calcium influx without release of calcium from intracellular stores. The diazoxide-induced rise in Cai was inhibited both by addition of 60 mM KCl to the assay buffer and by preincubation with glibenclamide, a specific K+ channel blocker. In addition, studies with the membrane potential-sensitive fluorescent probe bis-oxonol demonstrated that diazoxide hyperpolarized keratinocyte membranes. These findings suggest that keratinocytes possess K+ channels, and that the previously reported proliferation effects of K+ channel openers such as diazoxide on keratinocytes may result from hyperpolarization-induced elevation of Cai.

Chromosomal mapping of the genes for the human cell cycle proteins cyclin C (CCNC), cyclin E (CCNE), p21 (CDKN1) and KAP (CDKN3)

Many gene products associated with the cdk cell cycle kinases are thought to regulate the active kinase complex and thus regulate the transition points of the cell cycle. Genes encoding these proteins may potentially function as oncogenes or tumor suppressor genes. We describe the chromosomal mapping by FISH of the genes for several cdk-associated proteins including human CCNC (cyclin C) to 6q21, CCNE (cyclin E) to 19q12-->q13, CDKN1 (p21) to 6p21.2 and CDKN3 (KAP to 14q22). Some of these sites are near chromosomal translocations or LOH sites common to a variety of human tumors. The potential role for each of these genes in neoplasia is discussed.

Growth suppression by p18, a p16INK4/MTS1- and p14INK4B/MTS2-related CDK6 inhibitor, correlates with wild-type pRb function

The D-type cyclin-dependent kinases CDK4 and CDK6 are complexed with many small cellular proteins (p14, p15, p16, p18, and p20). We have isolated cDNA sequences corresponding to the MTS2 genomic fragment that encodes the CDK4- and CDK6-associated p14 protein. By use of a yeast interaction screen to search for CDK6-interacting proteins, we have also identified an 18-kD human protein, p18, that is a homolog of the cyclin D-CDK4 inhibitors p16 (INK4A/MTS1) and p14 (MTS2/INK4B). Both in vivo and in vitro, p18 interacts strongly with CDK6, weakly with CDK4, and exhibits no detectable interaction with the other known CDKs. Recombinant p18 inhibits the kinase activity of cyclin D-CDK6. Distinct from the p21/p27 family of CDK inhibitors that form ternary complexes with cyclin-CDKs, only binary complexes of p14, p16, and p18 were found in association with CDK4 and/or CDK6. Ectopic expression of p18 or p16 suppresses cell growth with a correlated dependence on endogenous wild-type pRb.

Transcriptional repression of the D-type cyclin-dependent kinase inhibitor p16 by the retinoblastoma susceptibility gene product pRb

Progression of the eukaryotic cell division cycle is regulated by a series of structurally related serine/threonine protein kinases known as cyclin-dependent kinases (CDKs). The D-type cyclin-dependent kinases, CDK4 and CDK6, have been strongly implicated in the control of G1 progression and the phosphorylation of the retinoblastoma protein, pRb. The formation of complexes and enzymatic activity of cyclin D-CDK4 and cyclin D-CDK6 kinases is negatively regulated by p16INK4 (MTS1/CDK4I/CDKN2) via its specific interaction with CDK4 and CDK6 catalytic subunits. Here we report that the p16 mRNA accumulates to a high level in cells lacking pRb function and transcription of p16 is repressed by pRb. Our results provide evidence supporting a feedback regulatory loop involving pRb, p16, and cyclin-dependent kinases.

Influence of humoral control peptides on medullary vasomotor control neurons: microstimulation and double-labeling studies using SHR and WKY rats

To study the influence of humoral control peptides on medullary vasomotor control neurons, angiotensin II (AII), arginine vasopressin (AVP) and atrial natriuretic peptide (ANP) were microinjected into three vasomotor control areas, i.e., the area postrema (AP), the nucleus tractus solitarii (NTS) and the rostral ventrolateral medulla (RVLM), of spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto rats (WKY), and the evoked cardiovascular response was observed. Unlike the injection areas, the threshold dose of one peptide for the cardiovascular response was similar, but the threshold dose differed from peptide to peptide. The threshold dose was lower for AII (0.15-0.29 pmol), in-between for ANP (0.9-1.5 pmol) and higher for AVP (14-30 pmol). No significant difference in the threshold dose was observed between SHR and WKY, suggesting that hypertension in SHR may not be due to the abnormal sensitivity to the three peptides of the vasomotor control neurons in the AP, NTS, and RVLM. The structural basis of the results of the microstimulation experiment was supported by the double-labeling study. The NTS neurons were innervated by (1) the AII-immunoreactive (ir) neurons in both sides of the lateral hypothalamic area (LH), the RVLM and the caudal ventrolateral medulla, and (2) the ANP-ir neurons in both sides of the paraventricular nucleus (Pa) and the LH. The RVLM neurons were innervated by (1) the AII-ir neurons in both sides of the LH and ipsilateral side of the lateral parabrachial nucleus (Pbl) and (2) the ANP-ir neurons in the ipsilateral Pbl. There was no evidence that the AVP-ir neurons in the Pa and the supraoptic nucleus innervate the NTS and the RVLM neurons, or that the AII, ANP or AVP-ir neurons innervate the AP neurons. This study suggests that in common with SHR and WKY rats AII and ANP may influence both the NTS and RVLM not by the humoral pathway but by the neural pathway, and AVP may not influence the three vasomotor control areas by the neural pathway.

Recognition of rotavirus antigens by mouse L3T4-positive T helper cells

A lymphocyte proliferation assay was used to examine the helper T cell response to rotavirus in mice following parenteral immunization with the UK strain of bovine rotavirus. Mixed populations of lymphocytes prepared from spleen or peripheral lymph nodes were tested for proliferation in the presence of UK strain rotaviruses, prepared as cell culture lysates, ultracentrifuged (pelleted) lysates, sucrose-purified virus and caesium chloride-purified virus. Live rotavirus induced non-specific stimulation of lymphocytes, which was not observed in response to inactivated virus. Putative helper T cells of the L3T4+ phenotype were prepared as an enriched population from UK strain-immunized mice or grown in vitro as a polyclonal T cell line. The response of L3T4(+)-enriched cells from mice immunized with inactivated virus was dependent on antigen-presenting cells (APCs). Cells obtained following immunization with live virus did not require further addition of APCs. The response of the L3T4+ T cell line was wholly dependent on APCs. UK strain-specific L3T4+ cells responded to whole UK rotavirus and to isolated VP6 of both UK and C486 rotavirus strains. The results indicate that virus-specific L3T4+ T cells are induced following rotavirus immunization and can respond to epitopes on VP6. UK strain-primed L3T4+ cells also responded to an avian rotavirus strain, Ch2, which shares only minimal serological cross-reactivity with the UK strain. T cell recognition of rotavirus may thus be broadly cross-reactive.

Cell cycle expression and p53 regulation of the cyclin-dependent kinase inhibitor p21

In normal human fibroblast cells, the primary cell cycle regulators, the cyclin-dependent kinases (CDKs), exist predominantly in multiple quaternary complexes, each consisting of a CDK, a cyclin, proliferating cell nuclear antigen (PCNA) and p21. p21 encodes a universal inhibitor of cyclin-dependent kinases. Here we show that the level of p21 mRNA and the interaction of p21 protein with cyclin-CDK enzymes are regulated during the cell cycle. When normal human fibroblast IMR90 cells were released from serum starvation, p21 mRNA reached its highest level immediately following serum stimulation, began to decrease at the G1/S boundary, fell to its lowest level during S phase, and accumulated again as cells exited from S phase. p21 protein associates with each cyclin-CDK complex in a cell cycle dependent manner. Cyclin A-CDK2-p21-PCNA and Cyclin B1-CDC2-p21-PCNA complexes are assembled in early S and G2 phase, respectively, indicating that p21 and/or PCNA regulates the enzymatic activity of each kinase at the time of their functioning. Cyclin D1-CDK4-p21-PCNA complexes, on the other hand, persist throughout the cell cycle, suggesting that cyclin D1-CDK4 quaternary complexes may play a role in monitoring an event(s) that may occur at any time, rather than at a specific stage of the cell cycle. The level of p21 mRNA in early passage Li-Fraumeni cells that are heterozygous for p53 mutation remained similar to that in normal fibroblasts, but was undetectable in immortalized Li-Fraumeni cells homozygous for mutant p53. This finding provides a plausible molecular explanation for the loss of genetic stability associated with cells homozygous, but not heterozygous, for p53 mutation.

Repression of cyclin D1: a novel function of MYC

Constitutive expression of human MYC represses mRNA levels of cyclin D1 in proliferating BALB/c-3T3 fibroblasts. We expressed a series of mutant alleles of MYC and found that downregulation of cyclin D1 is distinct from previously described properties of MYC. In particular, we found that association with Max is not required for repression of cyclin D1 by MYC in vivo. Conversely, the integrity of a small amino-terminal region (amino acids 92 to 106) of MYC is critical for repression of cyclin D1 but dispensable for transformation of established RAT1A cells. Runoff transcription assays showed that repression occurs at the level of transcription initiation. We cloned the promoter of the gene for human cyclin D1 and found that it lacks a canonical TATA element. Transcription starts at an initiator element similar to that of the adenovirus major late promoter; this element can be directly bound by USF in vitro. Expression of MYC represses the cyclin D1 promoter via core promoter elements and antagonizes USF-mediated transactivation. Taken together, our data define a new pathway for gene regulation by MYC and show that the cyclin D1 gene is a target gene for repression by MYC.

Neuronal expression of Fos protein in the paraventricular nucleus of the hypothalamus after i.p. injection of ulcergenic cinchophen

The purpose of this study was to identify the CNS neurons that express Fos protein after i.p. injection of ulcergenic drug cinchophen (300 mg/kg). This was done in unanesthetized Wistar rats with careful physiological controls. The population of Fos-immunoreactive (Fos-ir) neurons was the largest in the medial parvicellular part of the paraventricular nucleus of the hypothalamus (PVH). Distribution of Fos-ir neurons in the PVH corresponds with that of the parvicellular neurons in the PVH which secrete corticotropin-releasing hormone (CRH). This study strongly suggests that the cinchophen-induced peptic ulcer may originate in excitation of the CRH-secreting neurons in the parvicellular part of the PVH.

Regulation of fos-lacZ fusion gene expression in primary mouse epidermal keratinocytes isolated from transgenic mice

The expression of a fos-lacZ fusion gene was studied in primary mouse epidermal keratinocytes obtained from transgenic mice. This gene construct contains the entire upstream regulatory sequence of c-fos, and expression of the endogenous and fusion gene was shown by Northern analysis to correlate upon induction with the phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA). Using a chromogenic substrate of beta-galactosidase, we also demonstrated that expression of the fusion gene product, like that of Fos, was localized to the cell nucleus. In addition, we showed that epidermal keratinocytes responded to dialysed fetal bovine serum (FBS), TPA and high-calcium medium with enhanced Fos-lacZ expression and an inhibition of proliferation. The time course of induction of Fos-lacZ expression was similar for dialysed FBS and TPA, with a peak approximately 2 h after exposure. Exposure for approximately 24 h to an elevated extracellular calcium concentration was required to elicit an increase in Fos-lacZ expression. The lack of an immediate effect of raising medium calcium levels on Fos-lacZ expression contrasted with the rapidity of its effect on DNA synthesis, which was significantly inhibited within 6-8 h. In addition, we found that the protein kinase C inhibitor Ro 31-7549 blocked Fos-lacZ expression induced by TPA but had little or no effect on that elicited by high calcium levels. Thus, although our results indicate that the fos gene product may be involved in mediating epidermal keratinocyte growth arrest in response to differentiative agents such as FBS, TPA and high medium calcium levels, the exact role of this gene product remains unclear.

[Memory-enhancing effects of argipressin and its relationship with periaqueductal gray]

Wistar rats were trained to perform shuttle-box active avoidance response. In experiment A, 43 rats were implanted cannulae in bilateral periaqueductal gray (PAG) and argipressin (Arg) was injected. Arg 0.15 or 0.3 ng but not 0.05 ng retarded the extinction of avoidance response. In experiment B, 37 rats were set up bilateral electrolytic lesions of PAG or sham lesioned. Arg (6 micrograms.kg-1, ip) was injected after training. PAG lesions blocked the influence of ip Arg on memory enhancement. The results indicated that Arg may act directly on CNS to modulated memory and PAG may play an important role in this process. This observation provided further support to the previous suggestion that certain limbic midbrain structures were involved in memory-enhancement by Arg.

Protection of l-arginine against oxygen free radicals-injured rabbit aortic endothelium

This study was to investigate the protective effect of l-arginine, a precursor of endothelium-derived relaxing factor (EDRF), against damages due to endogenous or exogenous oxygen free radicals (OFR) on the aortic endothelium. The superfusion cascade bioassay of rabbit thoracic aorta was used. Endogenous OFR were generated by diethyldithiocarbamate (DETC) to deplete the cytosolic Zn-Cu form of superoxide dismutase (SOD). Exogenous OFR were generated by electrolysis of Krebs' solution. Acetylcholine (ACh) was infused through the donor aortic segment and relaxation of detector aortic ring was used as an indicator of the release of EDRF. The content of malondialdehyde (MDA) in the donor aorta was assayed biochemically. Both DETC and electrolysis inhibited vasodilator responses to ACh and increased MDA content in the aortic segment. Inhibition of DETC was abolished by exogenous SOD. l-Arginine improved impairment of endothelium-dependent relaxation and reduced elevation of MDA content by DETC or electrolysis. These results suggest that l-arginine presents a protective effect of endothelium against damage due to endogenous or exogenous OFR, and that the protective effect of l-arginine may be correlated with reduction in lipid peroxidation.

Increase of an endogenous inhibitor of nitric oxide synthesis in serum of high cholesterol fed rabbits

In the present study, the concentration of NG,NG-dimethylarginine (DMA), an endogenous inhibitor of nitric oxide synthesis, was measured with high-performance liquid chromatography, and the effect of hypercholesterolemia on DMA level was investigated in the high fat, high cholesterol fed rabbit. After 6 weeks on a high fat, high cholesterol diet, serum total cholesterol, triglycerides, and lipid peroxides were increased, and atherosclerosis was shown by means of morphological examination. In these rabbits with atherosclerosis, serum level of DMA was significantly raised, while serum creatine level remained normal. This study suggests that chronic hypercholesteremia may stimulate DMA production through elevation of lipid peroxides. The present results implicate endogenous DMA as a contributor to the development of atherosclerosis.

p21 is a universal inhibitor of cyclin kinases

Deregulation of cell proliferation is a hallmark of neoplastic transformation. Alteration in growth control pathways must translate into changes in the cell-cycle regulatory machinery, but the mechanism by which this occurs is largely unknown. Compared with normal human fibroblasts, cells transformed with a variety of viral oncoproteins show striking changes in the subunit composition of the cyclin-dependent kinases (CDKs). In normal cells, CDKs exist predominantly in multiple quaternary complexes, each containing a CDK, cyclin, proliferating cell nuclear antigen and the p21 protein. However, in many transformed cells, proliferating cell nuclear antigen and p21 are lost from these multiprotein enzymes. Here we have investigated the significance of this phenomenon by molecular cloning of p21 and in vitro reconstitution of the quaternary cell-cycle kinase complexes. We find that p21 inhibits the activity of each member of the cyclin/CDK family. Furthermore, overexpression of p21 inhibits the proliferation of mammalian cells. Our results indicate that p21 may be a universal inhibitor of cyclin kinases.

Expression, regulation, and production of tumor necrosis factor-alpha in mouse testicular interstitial macrophages in vitro

Tumor necrosis factor-alpha (TNF alpha) is a cytokine principally secreted from macrophages and monocytes activated by agents such as lipopolysaccharide (LPS). We have recently shown that TNF alpha inhibited mouse Leydig cell steroidogenesis in vitro. LPS injection has also been shown to repress Leydig cell function and induce TNF alpha messenger RNA (mRNA) expression in testicular interstitial macrophages in vivo. A paracrine regulation of Leydig cell testosterone synthesis by testicular interstitial macrophages via TNF alpha has been proposed. To further support this possibility, we examined whether LPS can induce TNF alpha mRNA expression and protein production in testicular interstitial macrophages in vitro. The regulation of LPS-stimulated TNF alpha mRNA expression in vitro was also investigated by employing the protein synthesis inhibitor cycloheximide (CHX). TNF alpha secretion into culture supernatants was examined by both bioassay and enzyme-linked immunosorbent assay. Isolated testicular interstitial macrophages were cultured for 24 h before the initiation of treatments. Cells were treated with or without LPS (1.0 micrograms/ml) and in the presence or absence of CHX (5.0 micrograms/ml) at different time points. Northern blot analysis showed that TNF alpha mRNA was rapidly and significantly induced by LPS in testicular interstitial macrophages. The peak expression was at 2 h after the treatment, which was 8.3 +/- 2.6-fold over the control (P < 0.05). TNF alpha mRNA then declined quickly and completely disappeared by 8 h after LPS treatment. In contrast to this rapid and transient induction of TNF alpha message by LPS alone, CHX extended the induction and caused a marked increase in LPS-induced TNF alpha mRNA at 2 and 6 h. CHX induced more LPS-stimulated TNF alpha mRNA at 6 h than that at 2 h. At 3 h after LPS treatment, TNF alpha secretion was significantly stimulated (5.6 +/- 1.2 U/micrograms macrophage DNA) measured by L929 tumor fibroblast cytotoxicity. TNF alpha was also detected by enzyme-linked immunosorbent assay in culture media of testicular interstitial macrophages treated with control medium or LPS for 1, 2, and 6 h. TNF alpha secretion was increased in a time-dependent way. There are significantly higher LPS-induced TNF alpha levels in culture media at 2 h (35.4 +/- 2.2 pg/micrograms macrophage DNA) and 6 h (85.5 +/- 11.1 pg/micrograms macrophage DNA) than those in control groups. The current study demonstrates that LPS activates testicular interstitial macrophages to express TNF alpha mRNA and secrete TNF alpha protein in vitro.

Proliferating cell nuclear antigen and p21 are components of multiple cell cycle kinase complexes

We have recently shown that two proteins, proliferating cell nuclear antigen (PCNA) and p21, are associated with cyclin D. Here we show that PCNA and p21 are common components of a wide variety of cyclin/cyclin-dependent kinase complexes in nontransformed cells. These include kinase complexes containing cyclin A, cyclin B, and cyclin D, associated either with CDC2, CDK2, CDK4, or CDK5. We show that PCNA and p21 form separate quaternary complex with each cyclin/CDK and that these quaternary complexes contain a substantial, if not major, fraction of the cell cycle kinases in asynchronously growing cells. These results suggest that PCNA and p21 may perform a common function for all these kinases.

[Delayed gastric liquid emptying in the patients with gastroesophageal reflux disease]

Although there were many reports on gastric emptying in patients with gastroesophageal reflux disease (GERD) in western country, there was no scientific paper about it in Chinese. In 22 cases of GERD, diagnosed by clinical manifestations, endoscopy, histology and 24-hour pH monitoring in the distal portion of esophagus, gastric liquid emptying was measured by using absorption test. The results suggested that the mean time to reach the peak of the serum paracetamol level after taking 500ml water was 34.02 +/- 9.09 min. in 13 healthy adults and 51.14 +/- 23.35 min. in 22 cases of GERD. The difference between the two groups was significant (P < 0.02). Among these 22 patients, 12(54.54%) had delayed gastric emptying, 1 rapid and 9 normal. Our data confirmed that gastric liquid emptying was delayed in some patients with GERD.

Subunit rearrangement of the cyclin-dependent kinases is associated with cellular transformation

In normal human diploid fibroblasts, cyclins of the A, B, and D classes each associate with cyclin-dependent kinases (CDKs), proliferating cell nuclear antigen (PCNA), and p21, thereby forming multiple independent quaternary complexes. Upon transformation of diploid fibroblasts with the DNA tumor virus SV40, or its transforming tumor antigen (T), the cyclin D/p21/CDK/PCNA complexes are disrupted. In transformed cells, CDK4 totally dissociates from cyclin D, PCNA, and p21 and, instead, associates exclusively with a polypeptide of 16 kD (p16). Quaternary complexes containing cyclins A or B1 and p21/CDK/PCNA also undergo subunit rearrangement in transformed cells. Both PCNA and p21 are no longer associated with CDC2-cyclin B1 binary complexes. Cyclin A complexes no longer contain p21, and a new 19-kD polypeptide (p19) is found in association with cyclin A. The pattern of subunit rearrangement of cyclin-CDK complexes in SV40-transformed cells is also shared in those containing adeno- or papilloma viral oncoproteins. Rearrangement also occurs in p53-deficient cells derived from Li-Fraumeni patients that carry no known DNA tumor virus. These findings suggest a mechanism by which oncogenic proteins alter the cell cycle of transformed cells.