Impaired germ cell development due to compromised cell cycle progression in Skp2-deficient mice

BACKGROUND: The gonads are responsible for the production of germ cells through both mitosis and meiosis. Skp2 is the receptor subunit of an SCF-type ubiquitin ligase and is a major regulator of the progression of cells into S phase of the cell cycle, which it promotes by mediating the ubiquitin-dependent degradation of p27, an inhibitor of cell proliferation. However, the role of the Skp2-p27 pathway in germ cell development remains elusive. RESULTS: We now show that disruption of Skp2 in mice results in a marked impairment in the fertility of males, with the phenotypes resembling Sertoli cell-only syndrome in men. Testes of Skp2(-/- )mice manifested pronounced germ cell hypoplasia accompanied by massive apoptosis in spermatogenic cells. Flow cytometry revealed an increased prevalence of polyploidy in spermatozoa, suggesting that the aneuploidy of these cells is responsible for the induction of apoptosis. Disruption of the p27 gene of Skp2(-/- )mice restored germ cell development, indicating that the testicular hypoplasia of Skp2(-/- )animals is attributable to the antiproliferative effect of p27 accumulation. CONCLUSION: Our results thus suggest that compromised cell cycle progression caused by the accumulation of p27 results in aneuploidy and the induction of apoptosis in gonadal cells of Skp2(-/- )mice. The consequent reduction in the number of mature gametes accounts for the decreased fertility of these animals. These findings reinforce the importance of the Skp2-p27 pathway in cell cycle regulation and in germ cell development

Reversion-inducing cysteine-rich protein with kazal motifs and matrix metalloproteinase-9 are prognostic markers in skull base chordomas

Prognosis of chordomas is difficult to predict based solely on histological findings. The purpose of this study was to assess expressions of reversion-inducing cysteine-rich protein with kazal motifs (RECK) and matrix metalloproteinase (MMP)-2, MMP-9 in skull base chordomas and to find out their correlations to outcome. Immunohistochemical study was performed in 19 samples (initial, n = 11; recurrent, n = 8) from 11 patients. The correlations among expression of RECK, MMP-2, MMP-9, and their prognostic values were analyzed. Significant correlation between RECK and MMP-9 was found, but there was no correlation found between MMP-2 and MMP-9. Higher MMP-9 expression significantly influenced outcome. Furthermore, MMP-9/RECK ratio showed significant correlation to outcome, showing their inverse relationship in the disease progress of skull base chordoma. RECK and MMP-9 can be valuable markers to predict prognosis in skull base chordomas.ArticleNEUROSURGICAL REVIEW. 33(2):167-173 (2010)journal articl

p107 inhibits G1 to S phase progression by down-regulating expression of the F-box protein Skp2

Cell cycle progression is negatively regulated by the pocket proteins pRb, p107, and p130. However, the mechanisms responsible for this inhibition are not fully understood. Here, we show that overexpression of p107 in fibroblasts inhibits Cdk2 activation and delays S phase entry. The inhibition of Cdk2 activity is correlated with the accumulation of p27, consequent to a decreased degradation of the protein, with no change of Thr187 phosphorylation. Instead, we observed a marked decrease in the abundance of the F-box receptor Skp2 in p107-overexpressing cells. Reciprocally, Skp2 accumulates to higher levels in p107−/− embryonic fibroblasts. Ectopic expression of Skp2 restores p27 down-regulation and DNA synthesis to the levels observed in parental cells, whereas inactivation of Skp2 abrogates the inhibitory effect of p107 on S phase entry. We further show that the serum-dependent increase in Skp2 half-life observed during G1 progression is impaired in cells overexpressing p107. We propose that p107, in addition to its interaction with E2F, inhibits cell proliferation through the control of Skp2 expression and the resulting stabilization of p27

Antigen p57/Kip2 as a potential negative regulator of human astrocytoma growth

This study was performed to determine the relationship between p57/Kip2 and the growth of human astrocytomas. Immunohistochemical staining for p57/Kip2, p53, p16, and Ki67 antigen was performed on paraffin-embedded tissue specimens obtained from 36 patients with astrocytoma. Expression of p57/Kip2, p53, p16, and Ki67 antigen was generally increased in association with the astrocytoma tumor grade. Expression of p16 was higher in patients whose tumors express p57/Kip2 in greater than 10% of tumor cells (p < 0.05). Expression of p53 also tended to be higher, but not to a statistically significant extent, in patients whose tumors express p57/Kip2 in greater than 10% of tumor cells. These findings suggest that p57/Kip2 inhibits the growth of human astrocytomas, and may function in parallel with p16 and p53. However, p57/Kip2 is, by itself, insufficient to arrest the cellular proliferation of human astrocytomas.ArticleJOURNAL OF CLINICAL NEUROSCIENCE. 16(12):1615-1618 (2009)journal articl

Conditional inactivation of Fbxw7 impairs cell-cycle exit during T cell differentiation and results in lymphomatogenesis

Cell proliferation is strictly controlled during differentiation. In T cell development, the cell cycle is normally arrested at the CD4+CD8+ stage, but the mechanism underlying such differentiation-specific exit from the cell cycle has been unclear. Fbxw7 (also known as Fbw7, Sel-10, hCdc4, or hAgo), an F-box protein subunit of an SCF-type ubiquitin ligase complex, induces the degradation of positive regulators of the cell cycle, such as c-Myc, c-Jun, cyclin E, and Notch. FBXW7 is often mutated in a subset of human cancers. We have now achieved conditional inactivation of Fbxw7 in the T cell lineage of mice and found that the cell cycle is not arrested at the CD4+CD8+ stage in the homozygous mutant animals. The mutant mice manifested thymic hyperplasia as a result of c-Myc accumulation and eventually developed thymic lymphoma. In contrast, mature T cells of the mutant mice failed to proliferate in response to mitogenic stimulation and underwent apoptosis in association with accumulation of c-Myc and p53. These latter abnormalities were corrected by deletion of p53. Our results suggest that Fbxw7 regulates the cell cycle in a differentiation-dependent manner, with its loss resulting in c-Myc accumulation that leads to hyperproliferation in immature T cells but to p53-dependent cell-cycle arrest and apoptosis in mature T cells

Ablation of Fbxw7 Eliminates Leukemia-Initiating Cells by Preventing Quiescence

SummaryImatinib eradicates dividing progenitor cells of chronic myeloid leukemia (CML) but does not effectively target nondividing leukemia-initiating cells (LICs); thus, the disease often relapse after its discontinuation. We now show that Fbxw7 plays a pivotal role in maintenance of quiescence in LICs of CML by reducing the level of c-Myc. Abrogation of quiescence in LICs by Fbxw7 ablation increased their sensitivity to imatinib, and the combination of Fbxw7 ablation with imatinib treatment resulted in a greater depletion of LICs than of normal hematopoietic stem cells in mice. Purging of LICs by targeting Fbxw7 to interrupt their quiescence and subsequent treatment with imatinib may thus provide the basis for a promising therapeutic approach to CML

Imprinted Cdkn1c genomic locus cell-autonomously promotes cell survival in cerebral cortex development

The cyclin-dependent kinase inhibitor p57KIP2 is encoded by the imprinted Cdkn1c locus, exhibits maternal expression, and is essential for cerebral cortex development. How Cdkn1c regulates corticogenesis is however not clear. To this end we employ Mosaic Analysis with Double Markers (MADM) technology to genetically dissect Cdkn1c gene function in corticogenesis at single cell resolution. We find that the previously described growth-inhibitory Cdkn1c function is a non-cell-autonomous one, acting on the whole organism. In contrast we reveal a growth-promoting cell-autonomous Cdkn1c function which at the mechanistic level mediates radial glial progenitor cell and nascent projection neuron survival. Strikingly, the growth-promoting function of Cdkn1c is highly dosage sensitive but not subject to genomic imprinting. Collectively, our results suggest that the Cdkn1c locus regulates cortical development through distinct cell-autonomous and non-cell-autonomous mechanisms. More generally, our study highlights the importance to probe the relative contributions of cell intrinsic gene function and tissue-wide mechanisms to the overall phenotype

Tissue-specific expression of histone H3 variants diversified after species separation

Additional file 3: Predicted CDS of human histone H3/H4 variants, contains Table S2, which lists the CDS locus information of the predicted human histone H3 and H4 variants in an Excel file

Mechanistic dissection of premature translation termination induced by acidic residues-enriched nascent peptide

Ribosomes polymerize nascent peptides through repeated inter-subunit rearrangements between the classic and hybrid states. The peptidyl-tRNA, the intermediate species during translation elongation, stabi-lizes the translating ribosome to ensure robust continuity of elongation. However, the translation of acidic residue-rich sequences destabilizes the ribosome, leading to a stochastic premature translation cessation termed intrinsic ribosome destabilization (IRD), which is still ill-defined. Here, we dissect the molecular mechanisms underlying IRD in Escherichia coli. Reconstitution of the IRD event reveals that (1) the prolonged ribosome stalling enhances IRD-mediated translation discontinuation, (2) IRD depends on temperature, (3) the destabilized 70S ribosome complex is not necessarily split, and (4) the destabilized ribosome is subjected to peptidyl-tRNA hydrolase-mediated hydrolysis of the peptidyl-tRNA without subunit splitting or recycling factors-mediated subunit splitting. Collectively, our data indicate that the translation of acidic-rich sequences alters the conformation of the 70S ribosome to an aberrant state that allows the noncanonical pre-mature termination