Epitope DNA vaccines against tuberculosis: spacers and ubiquitin modulates cellular immune responses elicited by epitope DNA vaccine

Cell-mediated immune responses are crucial in the protection against tuberculosis. In this study, we constructed epitope DNA vaccines (p3-M-38) encoding cytotoxic T lymphocyte (CTL) epitopes of MPT64 and 38 kDa proteins of Mycobacterium tuberculosis. In order to observe the influence of spacer sequence (Ala-Ala-Tyr) or ubiquitin (UbGR) on the efficacy of the two CTL epitopes, we also constructed DNA vaccines, p3-M-S(spacer)-38, p3-Ub (UbGR)-M-S-38 and p3-Ub-M-38. The immune responses elicited by the four DNA vaccines were tested in C57BL/6 (H-2b) mice. The cytotoxicity of T cells was detected by LDH-release method and by enzyme-linked immunospot assay for epitope-specific cells secreting interferon-gamma. The results showed that DNA immunization with p3-M-38 vaccine could induce epitope-specific CD8+ CTL response and that the spacer sequence (AAY) only enhanced M epitope presentation. The protein-targeting sequence (UbGR) enhanced the immunogenicity of the two epitopes. The finding that defined spacer sequences at C-terminus and protein-targeting degradation modulated the immune response of epitope string DNA vaccines will be of importance for the further development of multi-epitope DNA vaccines against tuberculosis.

[Effect of daphnetin on the exo-erythrocytic stage of rodent malaria]

OBJECTIVE

To investigate the activity of daphnetin(DPNT) against the exo-erythrocytic stage of rodent malaria.

METHODS

Groups of ten male ICR mice were infected by intraperitoneal injection with sporozoites of P. yoelii. Mice were administered daphnetin 0.5 hr postinfection on d0 and once per day for three additional consecutive days(d1-d3) by the i.g. route. The effects of daphnetin at various dosages and those of the combination of daphnetin with primaquine were assessed by the number of mice with negative Giemsa-stained slides from tail blood on the seventh day after infection and by the average number of red blood cells (RBC) infected in 1,000 RBC observed on the eleventh or twelfth day after infection. We also observed the effect of daphnetin on the concentration of Hb in ICR mice.

RESULTS

Daphnetin exhibited no detectable antimalarial effect on the exo-erythrocytic stage of P. yoelii, while the antimalarial efficacy of DPNT 50 mg/(kg.d) combined with 5 mg/(kg.d) PQ, was comparable to PQ 10 mg/(kg.d) x 4 d i.g. in mice infected with sporozoites of P. yoelii. The concentration of Hb in ICR mice administered with DPNT 50 mg/(kg.d) x 4 d decreased on the eighth day after administration.

CONCLUSION

Daphnetin alone showed no anti-exoerythrocytic activity in vivo. The combination of DPNT 50 mg/(kg.d) with PQ 5 mg/(kg.d) showed promising antimalarial efficacy comparable to that of PQ 10 mg/(kg.d). Administration of DPNT caused anemia in ICR mice.

[Immunostimulatory activity elicited by CpG sequences in Cysticercus cellulosae paramyosin cDNA]

OBJECTIVE

To analyse the immunostimulatory activity of CpG sequences in cysticercus cellulosae paramyosin (also named Antigen B, AgB) cDNA.

METHODS

C57BL/6 mice were immunized with pcDNA3-AgB plasmid, pcDNA3-AgB' (CpG sequences were mutated), pcDNA3 or AgB protein and two weeks later, immune response was assayed by ELISA.

RESULTS

IgG and IgG2a were detectable at week 2 after immunization and continually increased until week 4. The antibody levels elicited by pcDNA3-AgB were significantly higher(P < 0.05) than those elicited by others.

CONCLUSION

After pcDNA3-AgB plasmid inoculation, the immune response of mouse was elicited not only by the AgB protein but also by the CpG immunostimulatory sequences in the AgB cDNA.

The schizontocidal activity of daphnetin against malaria parasites in vitro and in vivo

OBJECTIVE

To investigate the in vitro and in vivo schizontocidal activity of daphnetin.

METHODS

Schizontocidal activity of daphnetin was tested using an in vitro assay based on the routine in vitro cultivation of P. falciparum FCC1 strain. The in vivo antimalarial effects of daphnetin at various dosages were assessed in mice infected with P. b. erghei ANKA according to "4-day suppress assay".

RESULTS

In vitro, daphnetin exhibited potent schizontocidal activity comparable to chloroquine(CQ) at the dose range of 1-10 mumol/L. In vivo, 50 or 100 mg/kg.d-1 x 4 d daphnetin i.g. and 10, 50 or 100 mg/kg.d-1 x 4 d dephnetin i.p. showed antimalarial efficacy comparable to CQ 10 mg/kg.d-1 x 4 d i.g. in mice infected with P. berghei ANKA, evaluated by both the reduction rate of parasitemia on D4 and the average surviving days in 30 days.

CONCLUSION

Daphnetin displays certain schizontocidal activity both in vitro and in vivo.

[Cloning of Cysticercus cellulosae AgB cDNA coding region]

OBJECTIVE

To amplify and clone Cysticercus cellulosae AgB cDNA coding region.

METHODS

The AgB cDNA was amplified by RT-PCR technique from the total RNA of Cysticercus cellulosae. It was cloned into the vector pUC118 and sequenced.

RESULTS

The PCR amplified product was a single band of 2.6 kb in size. The sequences of AgB cDNA coding region has 99.8% homology with that of Australian Cysticercus cellulosae, and their amino acid sequences have 99.3% homology.

CONCLUSION

Cysticercus cellulosae AgB cDNA coding region has been cloned successfully.

RNA-dependent RNA polymerase encoded by hepatitis C virus: biomedical applications

The hepatitis C viruses (HCVs) are a group of small enveloped RNA viruses that have been viewed as a leading cause of chronic hepatitis in humans. Infections by HCV represent a serious global health problem, because millions of people worldwide are infected and no efficient treatment is available at the present time. Since HCV was identified in 1989, considerable effort has been devoted to the discovery and development of novel molecules to treat HCV-related diseases. One of the approaches is the development of novel inhibitors that interrupt the normal functions of HCV NS5B, an RNA-dependent RNA polymerase essential to HCV replication. This review summarizes recent advances in the biochemical and structural understanding of HCV NS5B polymerase as well as in the development of antiviral agents targeting this important enzyme.

Recent advances in prevention and treatment of hepatitis C virus infections

Hepatitis C virus (HCV) is the leading cause of chronic hepatitis in humans. As members of the flavivirus family, HCVs are a group of small single-stranded, positive-sense RNA viruses. Upon translation of the genome, a polyprotein precursor is synthesized and further processed by both cellular and viral proteases to generate functional viral proteins. Treatment options are currently limited to the administration of alpha-interferon alone or in combination with ribavirin. Unfortunately, these approaches are characterized by relatively poor efficacy and an unfavorable side-effect profile. Therefore, intensive effort is directed at the discovery of novel molecules to treat this disease. These new approaches include the development of prophylactic and therapeutic vaccines, the identification of interferons with improved pharmacokinetic characteristics, and the discovery of novel drugs designed to inhibit the function of three major viral proteins: protease, helicase and polymerase. Finally, the HCV RNA genome itself, particularly the IRES element, is being actively exploited as an antiviral target using antisense molecules and catalytic ribozymes. This review summarizes the most recent findings in each of these areas. Although not intended to be comprehensive, it should serve as a first resource for those individuals who desire updated information in this rapidly changing field.

A novel luminescent copper(I) complex containing an acetylenediide-bridged, butterfly-shaped tetranuclear core

A novel luminescent acetylenediide-bridged tetranuclear copper(I) complex [Cu4(mu-Ph2Ppypz)4(mu 4-eta 1,eta 2-C identical to C)]-(ClO4)2 [Ph2Ppypz = 2-(diphenylphosphino-6-pyrazol-1-yl)pyridine] has been synthesized and structurally characterized by X-ray crystallography.

Argentophilicity and solvent-induced structural diversity in double salts of silver acetylide with silver perfluoroalkyl carboxylates

A series of novel double salts of silver(I) were isolated by dissolving Ag(2)C(2) in a concentrated aqueous solution of R(F)CO(2)Ag (R(F) = CF(3), C(2)F(5)) and AgBF(4). Different ancillary solvento ligands such as H(2)O, CH(3)CN, and C(2)H(5)CN were found to affect the crystallization process that led to the assembly of various silver(I) cages with embedded C(2)(2-) ions. 2Ag(2)C(2) x 12CF(3)CO(2)Ag x 5H(2)O (1) consists of two independent C(2)@Ag(7) cages, each having the shape of a basket with a square base. Ag(2)C(2) x 6CF(3)CO(2)Ag x 3CH(3)CN (2) contains a zigzag chain of edge-sharing triangulated dodecahedra, and 4Ag(2)C(2) x 23CF(3)CO(2)Ag x 7C(2)H(5)CN x 2.5H(2)O (3) features an unusual double-walled silver column constructed from the fusion of four different kinds of irregular polyhedra. Ag(2)C(2) x 10C(2)F(5)CO(2)Ag x 9.5H(2)O (4), Ag(2)C(2) x 9C(2)F(5)CO(2)Ag x 3CH(3)CN x H(2)O (5), and Ag(2)C(2) x 6C(2)F(5)CO(2)Ag x 2C(2)H(5)CN (6) all contain an edge-sharing double cage with each single cage in the shape of a square antiprism, a capped square antiprism, and a triangulated dodecahedron, respectively.

Identification and characterization of a monofunctional glycosyltransferase from Staphylococcus aureus

A gene (mgt) encoding a monofunctional glycosyltransferase (MGT) from Staphylococcus aureus has been identified. This first reported gram-positive MGT shared significant homology with several MGTs from gram-negative bacteria and the N-terminal glycosyltransferase domain of class A high-molecular-mass penicillin-binding proteins from different species. S. aureus MGT contained an N-terminal hydrophobic domain perhaps involved with membrane association. It was expressed in Escherichia coli cells as a truncated protein lacking the hydrophobic domain and purified to homogeneity. Analysis by circular dichroism revealed that secondary structural elements of purified truncated S. aureus MGT were consistent with predicted structural elements, indicating that the protein might exhibit the expected folding. In addition, purified S. aureus MGT catalyzed incorporation of UDP-N-acetylglucosamine into peptidoglycan, proving that it was enzymatically active. MGT activity was inhibited by moenomycin A, and the reaction product was sensitive to lysozyme treatment. Moreover, a protein matching the calculated molecular weight of S. aureus MGT was identified from an S. aureus cell lysate using antibodies developed against purified MGT. Taken together, our results suggest that this enzyme is natively present in S. aureus cells and that it may play a role in bacterial cell wall biosynthesis.

Recent advances in prevention and treatment of hepatitis C virus infections

Hepatitis C virus (HCV) is the leading cause of chronic hepatitis in humans. As members of the flavivirus family, HCVs are a group of small single-stranded, positive-sense RNA viruses. Upon translation of the genome, a polyprotein precursor is synthesized and further processed by both cellular and viral proteases to generate functional viral proteins. Treatment options are currently limited to the administration of alpha-interferon alone or in combination with ribavirin. Unfortunately, these approaches are characterized by relatively poor efficacy and an unfavorable side-effect profile. Therefore, intensive effort is directed at the discovery of novel molecules to treat this disease. These new approaches include the development of prophylactic and therapeutic vaccines, the identification of interferons with improved pharmacokinetic characteristics, and the discovery of novel drugs designed to inhibit the function of three major viral proteins: protease, helicase and polymerase. Finally, the HCV RNA genome itself, particularly the IRES element, is being actively exploited as an antiviral target using antisense molecules and catalytic ribozymes. This review summarizes the most recent findings in each of these areas. Although not intended to be comprehensive, it should serve as a first resource for those individuals who desire updated information in this rapidly changing field.

Activation of human rhinovirus-14 3C protease

The catalytic efficiency of human rhinovirus-14 (HRV14) 3C protease as a function of solvents and other regulators has been investigated using synthetic peptides as substrates. The proteolytic activity of HRV14 3C was found to be strongly stimulated by a series of anions in vitro and the activation was accompanied by changed Km, kcat, and increased kcat/Km values. A more than 72-fold increase in the 3C catalytic efficiency toward peptide substrates was observed in the presence of 0.8 M sodium sulfate. Several approaches, including size-exclusion chromatography and chemical cross-linking experiments, suggested that no oligomerization of the 3C enzyme occurred in the presence of activating anions. However, the anions did induce a significant conformational change of HRV14 3C protease, as revealed by circular dichroism spectrometry and tyrosine fluorescence analyses, which might contribute to 3C enzyme activation. Finally, the results obtained from 3C protease inhibitor studies suggested that the S1 specificity pocket of HRV14 3C was mainly affected by the activating anions. An induced-fit catalysis mechanism for viral proteases is discussed.

[Augmenter of liver regeneration: a novel cytokine]

Augmenter of liver regeneration (ALR) is a novel cytokine which specifically stimulates hepatic cell proliferation and is able to rescue acute liver failure caused by carbon tetrachloride. This article reviews the discovery, tissue distribution, functions and prospect of ALR and its relationship with hepatic stimulatory substance (HSS).

Protease inhibitors as potential antiviral agents for the treatment of picornaviral infections

The picornavirus family contains several human pathogens including human rhinovirus (HRV) and hepatitis A virus (HAV). In the case of HRVs, these small single-stranded positive-sense RNA viruses translate their genetic information into a polyprotein precursor which is further processed mainly by two viral proteases designated 2A and 3C. The 2A protease (2Apro) makes the first cleavage between the structural and non-structural proteins, while 3C protease (3Cpro) catalyzes most of the remaining internal cleavages. It has been shown that both 2Apro and 3Cpro are cysteine proteases but their overall protein folding is more like trypsin-type serine proteases. Due to their unique protein structure and essential roles in viral replication, 2Apro and 3Cpro have been viewed as excellent targets for antiviral intervention. In recent years, considerable efforts have been made in the development of antiviral compounds targeting these proteases. This article summarizes the recent approaches in the design of novel 2A and 3C protease inhibitors as potential antiviral agents for the treatment of picornaviral infections.

Biochemical characterization of signal peptidase I from gram-positive Streptococcus pneumoniae

Bacterial signal peptidase I is responsible for proteolytic processing of the precursors of secreted proteins. The enzymes from gram-negative and -positive bacteria are different in structure and specificity. In this study, we have cloned, expressed, and purified the signal peptidase I of gram-positive Streptococcus pneumoniae. The precursor of streptokinase, an extracellular protein produced in pathogenic streptococci, was identified as a substrate of S. pneumoniae signal peptidase I. Phospholipids were found to stimulate the enzymatic activity. Mutagenetic analysis demonstrated that residues serine 38 and lysine 76 of S. pneumoniae signal peptidase I are critical for enzyme activity and involved in the active site to form a serine-lysine catalytic dyad, which is similar to LexA-like proteases and Escherichia coli signal peptidase I. Similar to LexA-like proteases, S. pneumoniae signal peptidase I catalyzes an intermolecular self-cleavage in vitro, and an internal cleavage site has been identified between glycine 36 and histidine 37. Sequence analysis revealed that the signal peptidase I and LexA-like proteases show sequence homology around the active sites and some common properties around the self-cleavage sites. All these data suggest that signal peptidase I and LexA-like proteases are closely related and belong to a novel class of serine proteases.

Template requirements for RNA synthesis by a recombinant hepatitis C virus RNA-dependent RNA polymerase

The RNA-dependent RNA polymerase (RdRp) from hepatitis C virus (HCV), nonstructural protein 5B (NS5B), has recently been shown to direct de novo initiation using a number of complex RNA templates. In this study, we analyzed the features in simple RNA templates that are required to direct de novo initiation of RNA synthesis by HCV NS5B. NS5B was found to protect RNA fragments of 8 to 10 nucleotides (nt) from RNase digestion. However, NS5B could not direct RNA synthesis unless the template contained a stable secondary structure and a single-stranded sequence that contained at least one 3' cytidylate. The structure of a 25-nt template, named SLD3, was determined by nuclear magnetic resonance spectroscopy to contain an 8-bp stem and a 6-nt single-stranded sequence. Systematic analysis of changes in SLD3 revealed which features in the stem, loop, and 3' single-stranded sequence were required for efficient RNA synthesis. Also, chimeric molecules composed of DNA and RNA demonstrated that a DNA molecule containing a 3'-terminal ribocytidylate was able to direct RNA synthesis as efficiently as a sequence composed entirely of RNA. These results define the template sequence and structure sufficient to direct the de novo initiation of RNA synthesis by HCV RdRp.

S-nitrosothiols as novel, reversible inhibitors of human rhinovirus 3C protease

Human rhinovirus (HRV) 3C protease was inactivated by a series of S-nitrosothiols. These compounds exhibited different inhibitory activities in a time- and concentration-dependent manner with second-order rate constants (kinact/K(I)) ranging from 131 to 5360 M(-1) min(-1). The inactive enzyme could be re-activated by DTT, GSH and ascorbate, which indicated the inactivation mechanism was through an S-transnitrosylation process.

Changes in E2F binding after phenylbutyrate-induced differentiation of Caco-2 colon cancer cells

Differentiation agents use existing cellular systems to induce neoplastic cells to regain a normal phenotype and/or to cause growth arrest and therefore may offer novel chemotherapeutic approaches to treating solid tumors. In this study, we demonstrate in Caco-2 colon cancer cells that the differentiation agent phenylbutyrate (PB) causes a decrease in viable cells, an increase in cell differentiation, and a G1-S-phase block. The mechanism of this last effect is related to a PB-induced increase in p27Kip1, leading to a decrease in the activity of cyclin-dependent kinase 2 (CDK2), a positive regulator of the G1-S-phase cell cycle transition. Consistent with the decreased CDK2 kinase activity, we also observed a decrease in the phosphorylation state of the retinoblastoma protein after PB treatment. This was associated with increased binding and consequent inactivation of E2F, a transactivator of genes that regulate the G1 to S phase cell cycle transition. These data suggest that the differentiation agent PB inhibits tumor growth by limiting the availability of active E2F, with a subsequent G1-S-phase block. Additional studies should show whether PB is a clinically effective therapeutic agent against colorectal cancer.

Specificity and mechanism analysis of hepatitis C virus RNA-dependent RNA polymerase

The RNA-dependent RNA polymerase encoded by the hepatitis C virus (HCV) NS5B gene has been expressed as a nonfusion protein in bacterial cells and purified to homogeneity using sequential chromatographic columns. The purified NS5B protein exhibited RNA-dependent RNA polymerase activity using poly(A) template and the K(m) and V(max) were determined as 8.4 microM and 1976 pmol/mg-min, respectively. This full-length NS5B protein exhibited much stronger binding affinity toward the 30-mer poly(G) than other homopolymeric RNAs of the same size. For the first time, we demonstrate that the HCV NS5B was able to bind various ribonucleotides. Using a panel of oligonucleotides varying in length, we studied the NS5B catalytic efficiency and proposed the size of the NS5B active site to be 8-10 nucleotides. The multifunctional nature of NS5B protein is also discussed and compared with other viral RNA polymerases.

[An experimental study on inhibitory effect of xinjierkang granules on virus myocarditis]

OBJECTIVE

To investigate the inhibitory effect of Xinjierkang(XJEK) granules on virus myocarditis.

METHODS

Using a model mouse of virus myocarditis induced by coxsackie virus B3m (CVB3m) and mouse toxic myocarditis induced by adriamycin, a model of arrhythmia induced by BaCl2 and CHCl3, a model of inflammation caused by egg white and agar, along with a dynamic test of cardiac blood flow and an inhibitory test of CVB3m in vitro.

RESULTS

XJEK granules are efficacious in inhibiting CVB3m both in vitro and in vivo, protecting and curing virus myocarditis and toxic myocarditis in mice, reducing mouse death rate, serum level of LDH, AST and CK, titer of neutralizing antibodies, virus concentration of heart, and improving the abnormal ECG, pathological and ultrastructural damage of myocadium. The granules are also good for anti-inflammation, anti-myocardial ischemia, anti-arrhythmia, as well as for strengthening myocardiac contraction and increasing the serum IgG level.

CONCLUSION

Xinjerkang granules possess an inhibitory effect on virus myocarditis and toxic myocarditis.

p53/56(lyn) antisense shifts the 1,25-dihydroxyvitamin D3-induced G1/S block in HL60 cells to S phase

p53/56(lyn) is a member of the src family that is predominantly expressed in hematopoietic cells and is thought to play a role in cellular proliferation. In this study, we demonstrate the participation of p53/56(lyn) in 1,25-dihydroxyvitamin D(3) (1, 25D(3))-induced growth arrest in HL60 cells. We show that the mRNA and protein levels of p53/56(lyn) are markedly elevated after 1, 25D(3) treatment, which is accompanied by an increase of p53/56(lyn) kinase activity. We also demonstrate that treatment with p53/56(lyn) antisense oligodeoxynucleotides reverses the 1,25D(3)-induced G1/S block, and results in an accumulation of cells with S-phase DNA content. BrdU pulse-chase experiments reveal that this accumulation results from an increased proportion of cells actively synthesizing DNA, which are inhibited from exiting the S-phase compartment. These results indicate that upregulation of p53/56(lyn) contributes significantly to the G1/S growth arrest induced by 1,25D(3) in HL60 cells and thus its activation may be a desirable outcome of chemotherapeutic regimens.

De novo RNA synthesis catalyzed by HCV RNA-dependent RNA polymerase

The 65 kDa RNA-dependent RNA polymerase (NS5B), encoded by the hepatitis C virus (HCV) genome, is a key component involved in viral replication. Here we provide the direct evidence that purified HCV polymerase catalyzed de novo RNA synthesis in a primer-independent manner using homopolymers and HCV RNA as templates. The enzyme could utilize both polyC and polyU as templates for de novo RNA synthesis, suggesting that NS5B specifically recognized pyrimidine bases for initiation. More importantly, NS5B also catalyzed de novo RNA synthesis with an HCV RNA template; the resulting nascent RNA products, smaller than the template used, contained ATP as the first nucleotide. These results indicate that the newly synthesized RNAs did not result from template self-priming and suggest that a replication initiation site in the HCV RNA genome is a uridylate.

[Studies on antitussive, antiasthmatic, expectorant and anti-inflammatory effects of Jin'an kechuan granules]

OBJECTIVE

To study the pharmacologic effect of Jin'an Kechuan granules.

METHOD

Routine antitussive, antiasthmatic and expectorant methods were used.

RESULT

Jin'an Kechuan granules in the doses of 16, 8, 4 g.kg-1 ig could significantly decrease the frequency of cough caused by ammonia water in mice, and increase the secretion of phenol red from mouse tracheas in a dose-dependent manner. The granules also help increase the threshold voltage to induce cats to cough, prolong the latent period of asthma induced by histamine and acetylcholine mixture, and antagonize the contraction of isolated trachea strips induced by histamine and acetylcholine in guinea pigs. Jin'an Kechuan granules had inhibitory effects on common bacteria in the respiratory tract as well as on the swelling of acute inflammation in mice and rats.

CONCLUSION

Jin'an Kechuan granules have antitussive, antiasthmatic, expectorant and anti-inflammatory, antibacterial effects.

1,25-dihydroxyvitamin D(3)-induced retardation of the G(2)/M traverse is associated with decreased levels of p34(cdc2) in HL60 cells

Cellular differentiation of neoplastic cells after exposure to 1, 25-dihydroxyvitamin D(3) (1,25 D(3)) is accompanied by altered cell cycle regulation. In previous studies, blocks in both G(1)/S and G(2)/M checkpoints have been observed in 1,25D(3)-treated HL60 cells, but the mechanism of the 1,25D(3)-induced G(2)/M block has not been previously reported. In this study, we show by cell cycle analysis, using bromodeoxyuridine pulse-chase labeling, that the G(2)/M block in 1,25D(3)-treated HL60 cells is incomplete. We also demonstrate that although the 1,25D(3)-treated cells exhibit elevated levels of cyclin B1, Cdc25C, and Cdk7, which are positive regulators of the G(2)/M traverse, these cells have decreased protein levels of p34(cdc2) and decreased p34(cdc2) kinase activity. This provides potential mechanisms for the observed accumulation of cells in the G(2) cell cycle compartment and occasional polyploidization following treatment of HL60 cells with 1,25D(3). The data also suggest that the ability of some cells to traverse this block may be the result of cellular compensatory mechanisms responding to decreased p34(cdc2) activity by increasing the levels of other regulators of the G(2) traverse, such as cyclin B1, Cdc25C, and Cdk7.

Butyrate-induced G2/M block in Caco-2 colon cancer cells is associated with decreased p34cdc2 activity

Butyrate, a short-chain fatty acid, has been reported to inhibit proliferation and stimulate differentiation in multiple cancer cell lines. Whereas the effects of butyrate on cellular differentiation are well documented, the relationship between butyrate-induced differentiation and its effect on cell cycle traverse is less well understood. The purpose of this study was to investigate the effects of butyrate on the regulatory proteins of the G2/M traverse in the Caco-2 colon cancer cell model. We demonstrated that the inhibition of proliferation and increased cellular differentiation after treatment of Caco-2 cells with butyrate were associated with a significant G2/M cell cycle block. Although protein levels of the major G2/M regulatory protein, p34cdc2, were unchanged, a decrease in p34cdc2 activity was noted. Despite this decrease in activity, the inhibitory tyrosine phosphorylation of p34cdc2 was decreased, suggesting that other factors are responsible for the decreased kinase activity. The reduced activity of p34cdc2 provides a possible mechanism for the accumulation of Caco-2 cells in the G2/M cell cycle compartment following exposure to butyrate. This cell system provides a new model for studies of G2/M cell cycle perturbations.