Nuclear reprogramming: kinetics of cell cycle and metabolic progression as determinants of success.

Establishment of totipotency after somatic cell nuclear transfer (NT) requires not only reprogramming of gene expression, but also conversion of the cell cycle from quiescence to the precisely timed sequence of embryonic cleavage. Inadequate adaptation of the somatic nucleus to the embryonic cell cycle regime may lay the foundation for NT embryo failure and their reported lower cell counts. We combined bright field and fluorescence imaging of histone H(2b)-GFP expressing mouse embryos, to record cell divisions up to the blastocyst stage.

Delayed cell death associated with mitotic catastrophe in γ-irradiated stem-like glioma cells.

Background And Purpose: Stem-like tumor cells are regarded as highly resistant to ionizing radiation (IR). Previous studies have focused on apoptosis early after irradiation, and the apoptosis resistance observed has been attributed to reduced DNA damage or enhanced DNA repair compared to non-stem tumor cells. Here, early and late radioresponse of patient-derived stem-like glioma cells (SLGCs) and differentiated cells directly derived from them were examined for cell death mode and the influence of stem cell-specific growth factors.

Non-invasive in vivo imaging of tumor-associated CD133/prominin.

Background: Cancer stem cells are thought to play a pivotal role in tumor maintenance, metastasis, tumor therapy resistance and relapse. Hence, the development of methods for non-invasive in vivo detection of cancer stem cells is of great importance.

Methodology/principal Findings: Here, we describe successful in vivo detection of CD133/prominin, a cancer stem cell surface marker for a variety of tumor entities.

In vivo evaluation of a novel albumin-binding prodrug of doxorubicin in an orthotopic mouse model of prostate cancer (LNCaP).

PSA, which is overexpressed in prostate carcinoma, represents a molecular target for selectively releasing an anticancer agent from a prodrug formulation. In this study, we report on the in vivo antitumor efficacy of an efficacious albumin-binding prodrug of doxorubicin (PSA9) that incorporates p-aminobenzyloxycarbonyl (PABC) as a self-immolative spacer in addition to the heptapeptide, Arg-Ser-Ser-Tyr-Tyr-Ser-Leu, which serves as a substrate for PSA. The prodrug is cleaved very efficiently by PSA releasing H-Ser-Leu-PABC-doxorubicin and subsequently doxorubicin in PSA-positive cell lysates and prostate tumor homogenates as the final cleavage product.

Viability and DNA damage responses of TPPII-deficient Myc- and Ras-transformed fibroblasts.

Tripeptidyl peptidase II (TPPII) is a giant cytosolic protease. Previous protease inhibitor, overexpression and siRNA studies suggested that TPPII is important for viability and proliferation of tumor cells, and for their ionizing radiation-induced DNA damage response. The possibility that TPPII could be targeted for tumor therapy prompted us to study its role in transformed cells following genetic TPPII deletion.

Tripeptidyl peptidase II plays a role in the radiation response of selected primary cell types but not based on nuclear translocation and p53 stabilization.

The giant cytosolic protease tripeptidyl peptidase II (TPPII) was recently proposed to play a role in the DNA damage response. Shown were nuclear translocation of TPPII after gamma-irradiation, lack of radiation-induced p53 stabilization in TPPII-siRNA-treated cells, and complete tumor regression in mice after gamma-irradiation when combined with TPPII-siRNA silencing or a protease inhibitor reported to inhibit TPPII. This suggested that TPPII could be a novel target for tumor radiosensitization and prompted us to study radiation responses using TPPII-knockout mice.

Metaphase I arrest in LT/Sv mouse oocytes involves the spindle assembly checkpoint.

During meiotic maturation, the majority of oocytes from LT/Sv mice arrest at metaphase I. However, anaphase may be induced through parthenogenetic activation. If this happens within the ovary, it often results in the development of ovarian teratomas.

Hypomethylation of paternal DNA in the late mouse zygote is not essential for development.

Global demethylation of DNA which marks the onset of development occurs asynchronously in the mouse; paternal DNA is demethylated at the the zygote stage, whereas maternal DNA is demethylated later in development. The biological function of such asymmetry and its underlying mechanisms are currently unknown. To test the hypothesis that the early demethylation of male DNA may be associated with protamine-histone exchange, we ,used round spermatids, whose DNA is still associated with histones, for artificial fertilization (round spermatid injection or ROSI), and compared the level of methylation of metaphase chromosomes in the resulting zygotes with the level of methylation in zygotes obtained after fertilization using mature sperm heads (intracytoplasmic sperm injection or ICSI).

Germinal vesicle material drives meiotic cell cycle of mouse oocyte through the 3'UTR-dependent control of cyclin B1 synthesis.

We compared the profile of histone H1 kinase activity, reflecting Maturation Promoting Factor (MPF) activity in oocytes bisected at the germinal vesicle (GV) stage and allowed to mature as separate oocyte halves in vitro. Whereas the oocyte halves containing the nucleus exhibited the same profile of increased kinase activity as that typical for intact oocytes, the anuclear halves revealed strong inhibition of the increase in this activity soon after germinal vesicle breakdown (GVBD). In contrast, the profile of MAP kinase activity did not differ significantly between anuclear and nucleus-containing oocyte halves throughout maturation.

Oocyte nucleus controls progression through meiotic maturation.

We analyzed progression through the meiotic maturation in oocytes manipulated to replace the prophase oocyte nucleus with the nucleus from a cumulus cell, a pachytene spermatocyte or the pronucleus from a fertilized egg. Removal of the oocyte nucleus led to a significant reduction in histone H1 kinase activity. Replacement of the oocyte nucleus by a pronucleus followed by culture resulted in premature pseudomeiotic division and occasional abnormal cytokinesis; however, histone H1 kinase activity was rescued, microtubules formed a bipolar spindle, and chromosomes were condensed.

The spindle assembly checkpoint is not essential for CSF arrest of mouse oocytes.

In Xenopus oocytes, the spindle assembly checkpoint (SAC) kinase Bub1 is required for cytostatic factor (CSF)-induced metaphase arrest in meiosis II. To investigate whether matured mouse oocytes are kept in metaphase by a SAC-mediated inhibition of the anaphase-promoting complex/cyclosome (APC/C) complex, we injected a dominant-negative Bub1 mutant (Bub1dn) into mouse oocytes undergoing meiosis in vitro. Passage through meiosis I was accelerated, but even though the SAC was disrupted, injected oocytes still arrested at metaphase II.

The role of the destruction box and its neighbouring lysine residues in cyclin B for anaphase ubiquitin-dependent proteolysis in fission yeast: defining the D-box receptor.

Programmed proteolysis of proteins such as mitotic cyclins and Cut2/Pds1p requires a 9-residue conserved motif known as the destruction box (D-box). Strong expression of protein fragments containing destruction boxes, such as the first 70 residues of Cdc13 (N70), inhibits the growth of Schizosaccharomyces pombe at metaphase. This inhibition can be overcome either by removal of all lysine residues from N70 using site-directed mutagenesis (K0-N70) or by raising the concentration of intracellular ubiquitin.

cDNA cloning of bovine thrombospondin 1 and its expression in odontoblasts and predentin.

The extracellular matrix protein thrombospondin 1 (TSP1) was cloned from odontoblasts of bovine mandibular teeth which participate in dentinogenesis. The 5289 bp cDNA contains a complete open reading frame of 1170 amino acids. Bovine TSP1 has high homologies to its human and mouse counterparts.

The 26S proteasome: subunits and functions.

The 26S proteasome is an eukaryotic ATP-dependent, dumbbell-shaped protease complex with a molecular mass of approximately 2000 kDa. It consists of a central 20S proteasome, functioning as a catalytic machine, and two large V-shaped terminal modules, having possible regulatory roles, composed of multiple subunits of 25-110 kDa attached to the central portion in opposite orientations. The primary structures of all the subunits of mammalian and yeast 20S proteasomes have been determined by recombinant DNA techniques, but structural analyses of the regulatory subunits of the 26S proteasome are still in progress.

cDNA cloning and functional analysis of the p97 subunit of the 26S proteasome, a polypeptide identical to the type-1 tumor-necrosis-factor-receptor-associated protein-2/55.11.

Molecular cloning of cDNA for a new regulatory subunit, designated p97, of the human 26S proteasome showed that the polypeptide consists of 908 amino acid residues with a calculated molecular mass of 100184 Da and an isoelectric point of 4.94. Computer analysis showed that p97 is very similar to type-1 tumor-necrosis-factor (TNF)-receptor-associated protein (TRAP)-2 and 55.

CDNA cloning of p112, the largest regulatory subunit of the human 26s proteasome, and functional analysis of its yeast homologue, sen3p.

The 26S proteasome is a large multisubunit protease complex, the largest regulatory subunit of which is a component named p112. Molecular cloning of cDNA encoding human p112 revealed a polypeptide predicted to have 953 amino acid residues and a molecular mass of 105,865. The human p112 gene was mapped to the q37.

[Degradation mechanism of cell cycle factors by the proteasome].

Cell cycle progression is mainly controlled by the hetero-dimeric protein kinase complex named SPF (S-phase promoting factor) and MPF (M-phase promoting factor), consisting of CDKs and the regulator cyclins, which are involved in G1/S and G2/M transitions, respectively. Moreover, SPF is modulated by not only various oncoproteins positively, but also tumor suppresive gene products negatively. These regulator proteins are extremely unstable in cells, oscillating during cell cycle, and cell cycle stage-dependent destruction of specific factors is required for cell cycle progression, but molecular mechanism of their destabilization remains to be clarified.

Protein and gene structures of 20S and 26S proteasomes.

The two types of proteasomes with apparent sedimentation coefficients of 20S and 26S consist of a number of heterogeneous polypeptides and are unusually large protein complexes of approximately 750 kDa and 2000 kDa, respectively. The 26S proteasome is a cylindrical caterpillar-shaped complex with a symmetrical assembly of a four-layered central 20S proteasome and two terminal 22S regulators each with a V-like structure. The central core and the terminal structures are formed by multiple polypeptides with molecular masses of 21-31 kDa and 28-112 kDa, respectively.

Degradation of c-Fos by the 26S proteasome is accelerated by c-Jun and multiple protein kinases.

c-Fos is associated with c-Jun to increase the transcription of a number of target genes and is a nuclear proto-oncoprotein with a very short half-life. This instability of c-Fos may be important in regulation of the normal cell cycle. Here we report a mechanism for degradation of c-Fos.

cDNA cloning of p40, a regulatory subunit of the human 26S proteasome, and a homolog of the Mov-34 gene product.

The nucleotide sequence of a cDNA that encodes a new regulatory subunit, named p40, of the 26S proteasome of human hepatoblastoma HepG2 cells has been determined. The polypeptide predicted from the open reading frame consists of 324 amino acid residues with a calculated molecular mass of 37020 and isoelectric point of 6.03.

Thyroid hormone suppresses the differentiation of osteoprogenitor cells to osteoblasts, but enhances functional activities of mature osteoblasts in cultured rat calvaria cells.

The effects of thyroid hormone on osteoblastic differentiation and activity were studied in fetal rat calvaria (RC) cells cultured for up to 30 days in medium supplemented with thyroid hormone-depleted serum. In this condition, the cells proliferated and differentiated to form mineralized bone nodules (BN) and expressed osteoblastic markers such as alkaline phosphatase (ALP), osteocalcin (OCN), and osteopontin (OPN). The continuous presence of triiodothyronine (T3) at 10(-9)-10(-8) M in the medium inhibited the osteoblastic differentiation: 34% decrease in ALP activity on day 12 and 60% decrease in BN formation on day 15 at 10(-8) M.

Isolation and characterization of alpha-type HC3 and beta-type HC5 subunit genes of human proteasomes.

Eukaryotic proteasomes from an evolutionarily conserved multi-gene family and are thought to have originated from a common ancestral gene and diverged into alpha-type and beta-type subgroups. To understand the molecular basis of the proteasome genes, we isolated and characterized two human proteasome genes econding the alpha-type HC3 and beta-type HC5 subunit. The functional genes for HC3 and HC5 are similar in being approximately 15 kb in length, but differ in having exon numbers of 9 and 6, respectively.

Molecular structure of 20S and 26S proteasomes.

Eukaryotic proteasomes are unusually large protein complexes with characteristic sets of subunits and have been classified into two isoforms with apparent sedimentation coefficients of 20S and 26S, respectively. The 20S proteasome (previously named the multicatalytic proteinase complex) is a cylindrical particle with a molecular weight (MW) of approximately 750 kD. It is a dimeric assembly of two symmetrical discs, each consisting of 7 alpha-type subunits and 7 beta-type subunits, having the molecular organization alpha n[1-7)beta n[1-7)beta n[1-7)alpha n[1-7), where 'n' indicates the number of heterogeneous 7 subunits with MWs of 21-32 kD.