Cyclic AMP-responsive DNA-binding protein: structure based on a cloned placental cDNA

Cyclic AMP (cAMP) is an intracellular second messenger that activates transcription of many cellular genes. A palindromic consensus DNA sequence, TGACGTCA, functions as a cAMP-responsive transcriptional enhancer (CRE). The CRE binds a cellular protein of 38 kD in placental JEG-3 cells. A placental lambda gt11 library was screened for expression of specific CRE-binding proteins with the CRE sequence as a radioactive probe. A cDNA encoding a protein of 326 amino acids with the binding properties of a specific CRE-binding protein (CREB) was isolated. The protein contains a COOH-terminal basic region adjacent to a sequence similar to the "leucine zipper" sequence believed to be involved in DNA binding and in protein-protein contacts in several other DNA-associated transcriptional proteins including the products of the c-myc, c-fos, and c-jun oncogenes and GCN4. The CREB protein also contains an NH2-terminal acidic region proposed to be a potential transcriptional activation domain. The putative DNA-binding domain of CREB is structurally similar to the corresponding domains in the phorbol ester-responsive c-jun protein and the yeast transcription factor GCN4.

HBx protein of hepatitis B virus activates Jak1-STAT signaling

The X-gene product (HBx) of the hepatitis B virus plays essential roles in viral replication and the generation of hepatocellular carcinoma. Although the mechanism for HBx action is unclear, HBx may exert its pleiotropic functions through the stimulation of signal transduction pathways including the Ras/mitogen-activated protein kinase cascade and/or inactivation of the p53 function. Here, we investigated whether HBx has the ability to activate the Jak-STAT signaling pathway. As a first step, we established stable cell lines constitutively expressing HBx. In these HBx-expressing stable cells, the tyrosine phosphorylation of various STATs, including STAT3 and -5, was constitutively enhanced by HBx, and the concomitant increase in STAT-dependent DNA binding and transcriptional activation was observed. Furthermore, HBx specifically elevated tyrosine phosphorylation and in vitro kinase activity of Jak1, but not Jak2 or Tyk2, through protein to protein interaction with Jak1. These results clearly establish HBx as the inducer of the Jak-STAT signaling pathway, and at the same time, HBx-mediated Jak-STAT activation may provide a novel mechanism for the pleiotropic functions of HBx, including transformation and promiscuous transcriptional activation.

X-gene product of hepatitis B virus induces apoptosis in liver cells

Hepatitis B virus is a causative agent of hepatocellular carcinoma, and in the course of tumorigenesis, the X-gene product (HBx) is known to play important roles. Here, we investigated the transforming potential of HBx by conventional focus formation assay in NIH3T3 cells. Cells were cotransfected with the HBx expression plasmid along with other oncogenes including Ha-ras, v-src, v-myc, v-fos, and E1a. Unexpectedly, the introduction of HBx completely abrogated the focus-forming ability of all five tested oncogenes. In addition, the cotransfection of Bcl-2, an apoptosis inhibitor, reversed the HBx-mediated inhibition of focus formation, suggesting that the observed repression of focus formation by HBx is through the induction of apoptosis. Next, to test unequivocally whether HBx induces apoptosis in liver cells, we established stable Chang liver cell lines expressing HBx under the control of a tetracycline-inducible promoter. Induction of HBx in these cells in the presence of 1% calf serum resulted in typical apoptosis phenomena such as DNA fragmentation, nuclear condensation, and fragmentation. Based on these results, we propose that HBx sensitizes liver cells to apoptosis upon hepatitis B virus infection, contributing to the development of hepatitis and the subsequent generation of hepatocellular carcinoma.

Human hepatitis B virus X protein is a possible mediator of hypoxia-induced angiogenesis in hepatocarcinogenesis

The hepatitis B virus (HBV)-encoded transcriptional activator HBV-X protein (HBx) was known to be involved in hepatocarcinogenesis. Hepatocarcinogenesis generally included an active angiogenesis that was mainly considered to be due to a local hypoxia in liver tissues. However, the exact mechanisms of HBx-induced hepatocarcinogenesis were poorly understood. In this study, we examined the role of HBx in the increased angiogenesis and the possible regulating mechanisms of HBx by hypoxia. We demonstrated that HBx stimulated the transcription of vascular endothelial growth factor (VEGF), a potent angiogenic factor, in HBx-stable transfectants. HBx-induced angiogenesis was confirmed by in vivo tumor angiogenesis assay, resulting in that the HBx transfectants increased the formation of new blood vessels compared to the control transfectants. Then, we demonstrated that the expression of HBx was enhanced after incubating HBV-infected hepatoma cells under hypoxia. Moreover, the activity of HBV enhancer 1 (Enh1) was increased when hepatoma cells transfected with the reporter plasmid containing HBV Enh1 were exposed to hypoxic conditions. These results strongly suggest that HBx may play a critical role in the hypoxia-induced angiogenesis through transcriptional activation of VEGF during hepatocarcinogenesis.

Phosphotyrosine-independent binding of a 62-kDa protein to the src homology 2 (SH2) domain of p56lck and its regulation by phosphorylation of Ser-59 in the lck unique N-terminal region

A previously undescribed 62-kDa protein (p62) that does not contain phosphotyrosine but, nevertheless, binds specifically to the isolated src homology 2 (SH2) domain of p56lck has been identified. The additional presence of the unique N-terminal region of p56lck prevents p62 binding to the SH2 domain. However, phosphorylation at Ser-59 (or alternatively, its mutation to Glu) reverses the inhibition and allows interaction of the p56lck SH2 domain with p62. Moreover, p62 is associated with a serine/threonine kinase activity and also binds to ras GTPase-activating protein, a negative regulator of the ras signaling pathway. Thus, phosphotyrosine-independent binding of p62 to the p56lck SH2 domain appears to provide an alternative pathway for p56lck signaling that is regulated by Ser-59 phosphorylation.

Variation in response to growth factor stimuli in satellite cell populations

Variation in response to growth factor stimuli in myogenic satellite cell populations was investigated using a clonal-derived satellite cell culture system. Satellite cell clones were established from one muscle from one individual animal. One clone ("Early") which reached confluence on day 19 and one clone ("Late"), which reached confluence on day 29, were chosen for further examination. In previous studies, these two clones were found to differ in their growth rates in serum-containing medium. In the present study, the influence of growth factors on the proliferation of the two clones was compared in serum-free defined medium. Although basic fibroblast growth factor (bFGF), insulin-like growth factor-I (IGF-I), insulin, and platelet-derived growth factor-BB (PDGF-BB) stimulated proliferation of both clones, the Early clone was more responsive to all growth factors tested than the Late clone (P < or = 0.05). The Early clone was also more responsive to the proliferative and differentiative depressing effects of administered transforming growth factor-beta (P < or = 0.05). Examination of properties of the PDGF, FGF, and IGF-I receptors on these two clones revealed no differences in either dissociation constants or receptor numbers (P > or = 0.05). The results suggest that there is heterogeneity in satellite cell response to growth factors.

Purification and molecular cloning of a platelet aggregation inhibitor from the snake (Agkistrodon halys brevicaudus) venom

A platelet glycoprotein IIb-IIIa (GP IIb-IIIa) antagonist, salmosin, was purified to homogeneity from Korean snake (Agkistrodon halys brevicaudus) venom by means of chromatographic fractionations. We have isolated the cDNA encoding salmosin by using the cDNA library of the snake venom gland and analyzed its complete nucleotide sequence. The molecular identity was confirmed by comparison of the deduced amino acid sequence with the directly determined primary structure of salmosin. This protein is a single-chain polypeptide composed of 73 amino acids including 12 cysteines as well as the sequence Arg-Gly-Asp, a proposed recognition site of adhesive proteins. The primary sequence of salmosin shows considerable homology to previously described proteins of snake venom GP IIb-IIIa antagonist family. A molecular mass of 7474 for the protein was determined by matrix-assisted laser desorption ionization mass spectrometry. Salmosin inhibits GP IIb-IIIa binding to immobilized fibrinogen with an IC50 of 2.2 nM and ADP-induced platelet aggregation with an IC50 of 131 nM, respectively. This work demonstrates the purification, characterization, and cDNA cloning of salmosin, a platelet aggregation inhibitor that may have therapeutic potential as an antithrombotic agent.

Expression and characterization of a novel plasminogen activator from Agkistrodon halys venom

A venom gland cDNA library of Agkistrodon halys was constructed and screened with a probe based on the consensus sequence of venomic serine proteases. Next, we determined the sequences of the entire open reading frames of two selected positives which were found to encode novel serine proteases of 234 and 233 amino acids in length and named as Haly-PA and Haly 2, respectively. Upon protein data base search, Haly-PA showed the highest similarity of 82% to the previously characterized plasminogen activator, TSV-PA (Zhang et al. 1995, J. Biol. Chem. 270, 10246- 10255). Haly 2 displayed a 78% similarity to beta-fibrinogenase (Hung et al. 1994, B. B. R. C., 205, 1707 1715). Haly-PA was successfully expressed using the baculovirus system and secreted into the culture media as a 32 kDa glycoprotein. In the western analysis of snake venom, anti-Haly-PA antibody detected the same size of band indicating that this enzyme is a component of snake venom. Recombinant Haly-PA was purified to homogeneity using the combination of anion exchange and gel filtration column. In the fibrino(geno)lytic assay, recombinant Haly-PA displayed an indirect fibrino(geno)lytic activity depending on the presence of plasminogen and cleaved the plasminogen to generate the active plasimin. These results indicate that Haly-PA is a plasminogen activator and displays fibrino(geno)lytic activity through conversion of plasminogen to plasmin.

X-gene product antagonizes the p53-mediated inhibition of hepatitis B virus replication through regulation of the pregenomic/core promoter

Employing the glutathione S-transferase column retention method and far Western analysis, we found a physical association between tumor suppressor p53 and the hepatitis B virus X-gene product, which led us to study the function of observed interaction in relation to viral propagation. In the cell culture-based in vitro replication system, expression of p53 resulted in dramatic inhibition of viral replication, and this inhibition was relieved by the coexpression of the X-gene product in a dose-dependent manner. Furthermore, the activity of pregenomic/core promoter, responsible for the synthesis of pregenomic RNA, was almost completely inhibited upon expression of p53, and as in the replication assay, the inhibition was rescued by the coexpression of the X-gene product in a dose-dependent manner. Based on these results, we propose that the ratio of X-gene product to p53 is an important factor determining the fate of viral replication through modulation of the pregenomic/core promoter.

Unilateral inferior olive NMDA lesion leads to unilateral deficit in acquisition and retention of eyelid classical conditioning

New Zealand White rabbits (Oryctolagus cuniculus) were trained for acquisition (N = 21) or retention (N = 10) of classical eyelid conditioning with unilateral or bilateral N-methyl-DL-aspartate chemical lesions of the rostromedial dorsal accessory inferior olive (rmDAO; multiple injections totaling 76 to 342 nmol). In all instances, subjects were unable to learn or retain conditioning on the side contralateral to the lesion. Learning rates were comparable for lesions outside of the rmDAO and sham operates. These findings demonstrate a specific unilateral deficit whereas in previous research the answer to this question was ambiguous since electrolytic lesions effectively cause bilateral olivary lesions. This research agrees with the concept that the inferior olive projects essential information about the unconditioned stimulus to a cerebellar locus of learning and memory for classical conditioning.

Through induction of juxtaposition and tyrosine kinase activity of Jak1, X-gene product of hepatitis B virus stimulates Ras and the transcriptional activation through AP-1, NF-kappaB, and SRE enhancers

Here, based on the recent finding of HBx (X-gene product of hepatitis B virus) as the inducer of Jak1, we investigated the mechanism for the HBx-mediated host cell regulation and found that (i) HBx associates specifically with Jak1 in vivo; (ii) HBx itself forms a dimer which leads to juxtaposition of associated Jak1 and subsequent activation of the tyrosine kinase activity of Jak1; (iii) HBx-mediated activation of the promoters containing AP-1-, NF-kappaB-, SRE-, and SIE-sites is dependent on the activation of Jak1; (iv) Jak1, once activated by HBx, induces Ras activity through recruitment of Grb2 and induces tyrosine phosphorylation of Raf1, but not shc. These findings show that previously reported functions of HBx, such as activation of multiple signaling pathways and transcriptional activation are attributable to HBx-mediated Jak1 activation.

Estrogen-like activity of cyclic peptides from Vaccaria segetalis extracts

Methanol and ethyl acetate extracts of Wang Bu Liu Xing (seeds of Vaccaria segetalis, Caryophyllaceae) and cyclic peptides (named segetalins A and B) obtained from the extracts were shown to have an estrogen-like activity.

Liver-specific enhancer II is the target for the p53-mediated inhibition of hepatitis B viral gene expression

Here, we established the inhibitory mechanism of p53 on hepatitis B viral gene expression using HepG2 cells. Our results are as follows. First, p53 down-regulated the activities of all four promoters of hepatitis B virus (HBV), suggestive of the presence of a common element mediating the p53-dependent transcriptional repression. Second, employing the 5'-deletion constructs of the pregenomic/core promoter, the liver-specific enhancer II region was localized as a target for the p53-mediated transcriptional repression. Third, in a detailed analysis of the enhancer II region, the 5'-proximal 31-base pair region was defined as a p53-repressible element. Throughout the study, p53-mediated repression was rescued upon coexpression of the X-gene product, HBx. Finally, in an electrophoretic mobility shift assay, the defined p53-repressible element did not bind purified p53 directly, but shifted three bands in HepG2 nuclear extract, two of which was supershifted upon addition of p53 monoclonal antibody. These results display a novel mechanism of p53-dependent transcriptional repression in which p53 negatively regulates the viral-specific DNA enhancer through protein to protein interaction with an enhancer-binding protein. At the same time, the results indicate that p53 plays a defensive role against HBV by transcriptionally repressing the HBV core promoter through liver-specific enhancer II and HBx is required to counteract this inhibitory function of p53.

Direct interaction of the CD38 cytoplasmic tail and the Lck SH2 domain. Cd38 transduces T cell activation signals through associated Lck

CD38 ligation has been shown to induce activation of intracellular signaling cascade in T lymphocytes through a Lck-dependent pathway. However, it is not clear how Lck initiates the CD38-mediated signaling process. In the present study, we showed that CD38 and Lck were physically associated through the cytoplasmic tail and the Src homology 2 domain, respectively. This was evidenced by coimmunoprecipitation of Lck with CD38 and Lck with isolated CD38 cytoplasmic domain from T cell lysate, cell lysate of COS-7 cells cotransfected with cDNAs of Lck and CD38, or a mixture of in vitro translated CD38 and Lck. Because the CD38 cytoplasmic domain does not contain any tyrosine residue, the interaction should be independent of phosphotyrosine. The interaction was further confirmed by in vitro interaction between a purified Lck Src homology 2 domain and a nonphosphosynthetic peptide corresponding to the membrane proximal region of the CD38 cytoplasmic domain. In addition, CD38 ligation resulted in an elevated tyrosine kinase activity of the CD38-associated Lck and ultimate activation of interleukin-2 gene transcription. Furthermore, expression of a kinase-deficient Lck mutant suppressed interleukin-2 gene activation in a dose-dependent manner. These results strongly suggested that CD38 ligation indeed tranduced signals for T cell activation using its associated Lck.

Adaptor protein Lad relays PDGF signal to Grb2 in lung cells: a tissue-specific PDGF signal transduction

Lad was previously identified as an adaptor protein binding to the SH2 domain of Lck (1). Specific detection of Lad mRNA in lung cells, as well as, in T cells led us to investigate the signaling pathways regulating Lad in lung cells. We found that (i) upon PDGF stimulation, Lad expression is induced in lung cells, especially in the bronchial epithelial cells; (ii) Lad is tyrosine phosphorylated upon PDGF stimulation and is associated with PDGF receptor; (iii) upon PDGF stimulation, Grb2 is recruited to Lad in human embryonic lung cells; (iv) overexpression of Lad elevated AP-1 promoter activity by two- to threefold, whereas dominant negative Lad abrogated PDGF-dependent activation of AP-1 promoter. These results provide a novel mechanism of PDGF-dependent signaling, in which Lad acts as an adaptor in a tissue-specific manner, linking PDGF signal to Grb2 and subsequent activation of AP-1.

Characterization of a cAMP-regulated enhancer-binding protein

The transcription regulation of many hormone genes is modulated by intracellular second messengers such as cAMP. The cAMP response element binding protein, CREB, binds to the 8 base pair CRE enhancer, TGACGTCA, that is found in the 5'-flank of certain genes including those for somatostatin and the alpha-subunit of human chorionic gonadotropin. The recent characterization of CREB and CREB-related cDNA clones, combined with Southwesterns and Northern blot analyses, reveals a family of transcription factors that dimerize via a leucine zipper motif and bind to the CRE through positively charged basic regions. The CREB cDNA encoding a 327 residue protein is transcriptionally activated via phosphorylation by protein kinases, including the cAMP-dependent protein kinase-A.

Comparison of growth factor receptors and metabolic characteristics of satellite cells derived from the biceps femoris and pectoralis major muscles of the turkey

Myogenic satellite cells were isolated from the turkey pectoralis major (PM), a muscle composed largely of white fibers, and the biceps femoris (BF), a muscle composed largely of red fibers, and their properties were compared in culture. Satellite cells derived from the PM and BF muscles exhibited differences in metabolic parameters, growth factor receptor characteristics, and mitogenic responses. PM satellite cells exhibited greater responsiveness to platelet-derived growth factor (PDGF), and the PDGF receptor on these cells had a higher affinity toward ligand compared to BF cells (P < 0.05). Protein synthesis, protein degradation, and glucose uptake rates were higher in BF satellite cell cultures (P < 0.05), correlating with previously reported in vivo measurements using red and white muscle fibers.

Natural history and factors associated with ulnar-sided wrist pain in distal radial fractures treated by plate fixation

We documented longitudinal changes in the incidence of ulnar-sided wrist pain after distal radial fractures treated by plate fixation and identified factors associated with ulnar-sided wrist pain. A total of 140 patients were enrolled in this study. Radiographs were taken 3 months after operation, and were used to measure radial inclination, anterior angulation and ulnar variance, and to identify the presence of an ulnar styloid fracture. Clinical assessments at the same time included grip strengths, ranges of wrist motion and the patient-rated wrist evaluation questionnaire. The presence of ulnar-sided wrist pain was noted at each follow-up visit. The incidence of ulnar-sided wrist pain decreased significantly with time after surgery (22 patients at 3 months, 11 patients at 6 months and three patients at 12 months). The mean age, sex, the presence of an ulnar styloid fracture and the classification of the distal radial fracture were not factors that were associated with a higher incidence of ulnar-sided wrist pain, but there was an association between higher patient-rated wrist evaluation scores and the presence of ulnar-sided wrist pain.

LEVEL OF EVIDENCE

Prognosis, Level IV.

Identification of genetic polymorphisms in bovine mitochondrial deoxyribonucleic acid

In this study, the intent was to identify genetic polymorphisms of mitochondrial (mt) DNA in Korean cattle (Bos taurus coreana) and to analyze the genetic relationship between Korean cattle and other breeds. Whole mtDNA genomes (16,338 bp) of 26 animals (16 Korean cattle and 10 Holsteins) were directly sequenced. Multiple alignments, including 26 whole-mtDNA sequences obtained by direct sequencing and 10 mtDNA sequences from a public database (National Center for Biotechnology Information), revealed 393 mtDNA polymorphisms (382 SNP, 3 heteroplasmies, and 8 insertion-deletion polymorphisms). Estimated gene diversity of mtDNA was 0.00198 among these 36 animals. Phylogenic analysis with mtDNA polymorphisms revealed a distinct genetic difference between Bos taurus (Korean, Japanese Black, Holstein, and Fleckvieh breeds) and Bos indicus (Nellore and Zwergzebu breeds). The genetic information regarding mtDNA polymorphisms identified in this study would be useful for further investigation of mtDNA in other breeds.