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H Nagahara

Publications and source records attributed to H Nagahara.

17 recordsLinked to original sources
PubMed1999

Transforming growth factor beta targeted inactivation of cyclin E:cyclin-dependent kinase 2 (Cdk2) complexes by inhibition of Cdk2 activating kinase activity.

Transforming growth factor beta (TGF-beta)-mediated G(1) arrest previously has been shown to specifically target inactivation of cyclin D:cyclin-dependent kinase (Cdk) 4/6 complexes. We report here that TGF-beta-treated human HepG2 hepatocellular carcinoma cells arrest in G(1), but retain continued cyclin D:Cdk4/6 activity and active, hypophosphorylated retinoblastoma tumor suppressor protein. Consistent with this observation, TGF-beta-treated cells failed to induce p15(INK4b), down-regulate CDC25A, or increase levels of p21(CIP1), p27(KIP1), and p57(KIP2). However, TGF-beta treatment resulted in the specific inactivation of cyclin E:Cdk2 complexes caused by absence of the activating Thr(160) phosphorylation on Cdk2. Whole-cell lysates from TGF-beta-treated cells showed inhibition of Cdk2 Thr(160) Cdk activating kinase (CAK) activity; however, cyclin H:Cdk7 activity, a previously assumed mammalian CAK, was not altered. Saccharomyces cerevisiae contains a genetically and biochemically proven CAK gene, CAK1, that encodes a monomeric 44-kDa Cak1p protein unrelated to Cdk7. Anti-Cak1p antibodies cross-reacted with a 45-kDa human protein with CAK activity that was specifically down-regulated in response to TGF-beta treatment. Taken together, these observations demonstrate that TGF-beta signaling mediates a G(1) arrest in HepG2 cells by targeting Cdk2 CAK and suggests the presence of at least two mammalian CAKs: one specific for Cdk2 and one for Cdk4/6.

CDC2-CDC28 Kinases↗
PubMed1999

Transduced p16INK4a peptides inhibit hypophosphorylation of the retinoblastoma protein and cell cycle progression prior to activation of Cdk2 complexes in late G1.

Progression of cells through the G1 phase of the cell cycle requires cyclin D:Cdk4/6 and cyclin E:Cdk2 complexes; however, the duration and ordering of these complexes remain unclear. To address this, we synthesized a peptidyl mimetic of the Cdk4/6 inhibitor, p16INK4a that contained an NH2-terminal TAT protein transduction domain. Transduction of TAT-p16 wild-type peptides into cells resulted in the loss of active, hypophosphorylated pRb and elicited an early G1 cell cycle arrest, provided cyclin E:Cdk2 complexes were inactive. We conclude that cyclin D:Cdk4/6 activity is required for early G1 phase cell cycle progression up to, but not beyond, activation of cyclin E:Cdk2 complexes at the restriction point and is thus nonredundant with cyclin E:Cdk2 in late G1.

CDC2-CDC28 Kinases↗
PubMed1997

Hypo-phosphorylation of the retinoblastoma protein (pRb) by cyclin D:Cdk4/6 complexes results in active pRb.

In cycling cells, the retinoblastoma protein (pRb) is un- and/or hypo-phosphorylated in early G1 and becomes hyper-phosphorylated in late G1. The role of hypo-phosphorylation and identity of the relevant kinase(s) remains unknown. We show here that hypo-phosphorylated pRb associates with E2F in vivo and is therefore active. Increasing the intracellular concentration of the Cdk4/6 specific inhibitor p15(INK4b) by transforming growth factor beta treatment of keratinocytes results in G1 arrest and loss of hypo-phosphorylated pRb with an increase in unphosphorylated pRb. Conversely, p15(INK4b)-independent transforming growth factor beta-mediated G1 arrest of hepatocellular carcinoma cells results in loss of Cdk2 kinase activity with continued Cdk6 kinase activity and pRb remains only hypo-phosphorylated. Introduction of the Cdk4/6 inhibitor p16(INK4a) protein into cells by fusion to a protein transduction domain also prevents pRb hypo-phosphorylation with an increase in unphosphorylated pRb. We conclude that cyclin D:Cdk4/6 complexes hypo-phosphorylate pRb in early G1 allowing continued E2F binding.

Carrier Proteins↗
PubMed1995

Characterization of Japanese families with early-onset type 2 (non-insulin dependent) diabetes mellitus and screening for mutations in the glucokinase and mitochondrial tRNA(Leu(UUR)) genes.

Genetic linkage studies of families with early-onset type 2 diabetes have facilitated the identification of diabetes-susceptibility genes. In order to assess the feasibility of using linkage approaches to identify genes responsible for the development of type 2 diabetes in Japanese subjects, we examined our clinical records for multigenerational families suitable for genetic studies. We identified 16 families in which at least one subject was diagnosed with type 2 diabetes before 25 years of age. Seven of these families had a pattern of inheritance consistent with a diagnosis of maturity-onset diabetes of the young (MODY) and nine families showed a complex pattern of inheritance of type 2 diabetes with transmission of diabetes-susceptibility genes from both parents. The glucokinase and mitochondrial tRNA(Leu(UUR)) genes were screened for mutations in at least one affected subject from each family in order to assess the contribution of mutations in these genes to the development of the diabetes. No mutations were found, which suggests that the diabetes in these families resulted from mutations in other genes.

Adolescent↗
PubMed1989

Permanent conversion of mouse and human cells transformed by activated ras or raf genes to apparently normal cells by treatment with the antibiotic azatyrosine.

Azatyrosine [L-beta-(5-hydroxy-2-pyridyl)-alanine], an antibiotic isolated from Streptomyces chibanensis, inhibited the growth of NIH 3T3 cells transformed by the activated human c-Ha-ras gene but did not significantly inhibit the growth of normal NIH 3T3 cells. Surprisingly, upon treatment with azatyrosine most of the transformed cells apparently became normal. These apparently normal cells, named revertant cells, grew in the presence of azatyrosine and stopped growing when they reached confluency, and their normal phenotype persisted during prolonged culture in the absence of azatyrosine. The revertant cells did not grow in soft agar and scarcely proliferated in nude mice. The human c-Ha-ras gene present in transformed NIH 3T3 cells was still present in the revertant cells and was expressed to the same extent as in the original transformed cells, producing the same amount of activated p21. Treatment with azatyrosine caused similar conversion of NIH 3T3 cells transformed by activated c-Ki-ras, N-ras, or c-raf to apparently normal cells, but NIH 3T3 cells transformed by hst or ret were not exclusively converted by azatyrosine. Human pancreatic adenocarcinoma cells, which are known to contain an amplified activated c-Ki-ras gene and an amplified c-myc gene, were also converted to flat and giant revertant cells by treatment with azatyrosine.

Alanine↗
PubMed1987

A 29 kDa GTP-binding protein expressed in mouse brain, lung, kidney, spleen and transformed NIH3T3 cells.

A novel 29 kDa GTP-binding protein has been detected in mouse brain, kidney, lung and spleen. The binding property is specific for guanine nucleotides, and the binding activity for GTP is retained after transfer of the 29 kDa protein to a nitrocellulose membrane. The 29 kDa protein is also expressed in NIH3T3 cells transformed by activated human c-Ha-ras, hst, ret and c-raf. The 29 kDa protein present constitutively in some mouse tissues is possibly involved in some cellular signal transduction relevant to the function of these tissues. In addition, its function may play a role in phenotype of transformed cells.

Animals↗
PubMedDate not supplied

Loss of heterozygosity on chromosome 16 in hepatocellular carcinoma.

In order to understand the molecular genetics of human hepatocellular carcinoma (HCC) a common chromosomal abnormality in HCC was examined using restriction fragment length polymorphism (RFLP) analysis. Sixty-eight HCC specimens were examined for loss of heterozygosity at 11 different chromosomal arms including 1p, 5p, 11p, 11q, 13q, 14q, 15q, 16p, 16q, 18q, and 19q. Losses were not detected on chromosome 1, 5, 14, 15 or 19, and the frequencies of losses were low (11-19%) for chromosomes 11, 13 and 18. In contrast, loss of heterozygosity was frequently observed for three different loci on chromosome 16, the HBA locus at 16p13.3 (22%), the MT2 locus at 16q21-22.1 (15%) and the HP locus at 16q22.1-22.2 (39%). There was no remarkable difference in the frequencies of loss of heterozygosity at these loci among HBV related HCC, HCV related HCC and neither virus (NBNC) related HCC. Thus, the results indicate that at least three different genetic abnormalities in chromosome 16 are commonly observed in various HCC, and that this chromosome may have some important role(s) in recessive genetic changes which generate this tumour.

Alleles↗
PubMedDate not supplied

Clinical evaluation of a newly established anti-HCV assay for the diagnosis of hepatitis C in Japan.

To develop a more dependable method of diagnosing hepatitis C, serum anti-hepatitis C virus (HCV) was examined by using a new assay (anti-HCV second generation). The results were compared with those of either the conventional assay (anti-HCV first generation) or HCV-RNA analysis. With the first generation assay, anti-HCV was detected in 69% of post-transfusion acute hepatitis (AH), 44% of sporadic AH, 50% of needlestick exposed AH, 72% of chronic hepatitis (CH), 77% of liver cirrhosis (LC) and 86% of hepatocellular carcinoma (HCC). These results were remarkably increased by using the second generation assay (92% in post-transfusion AH, 72% in sporadic AH, 100% in needlestick exposed AH, 96% in CH, 96% in LC and 97% in HCC). Furthermore, in the early stages of AH (from 1-5 weeks after onset), anti-HCV was not detected in all 18 patients by the first generation assay, but was found in 10 of them by using the second generation assay. The failure to detect anti-HCV with the first generation assay was mainly due to a lack of the core region coding peptide (C22-3) in this assay. In the AH-resolving group, anti-HCV second generation did not disappear, but the titre tended to be lower than that in the CH-developing group. Thus, the second generation assay for anti-HCV was considered to be a more useful tool for not only the diagnosis of hepatitis C but also for determining prognosis.

Adult↗