Cdk2 and Cdk4 cooperatively control the expression of Cdc2

Progression through the mammalian cell cycle is associated with the activity of four cyclin dependent kinases (Cdc2/Cdk1, Cdk2, Cdk4, and Cdk6). Knockout mouse models have provided insight into the interplay of these Cdks. Most of these models do not exhibit major cell cycle defects revealing redundancies, and suggesting that a single Cdk might be sufficient to drive the cell cycle, similar as in yeast. Recent work on Cdk2/Cdk4 double knockouts has indicated that these two Cdks are required to phosphorylate Rb during late embryogenesis. The lack of Rb phosphorylation is progressive and associated with reduced E2F-inducible gene expression. Cdk2 and Cdk4 share the essential function of coupling the G1/S transition with mitosis. However, proliferation in early embryogenesis appears to be independent of Cdk2 and Cdk4. We discuss these observations and propose molecular mechanisms that establish the requirement for Cdk2 and Cdk4 at the G1/S transition. We are considering that the balance between proliferation and differentiation is disturbed, which affects especially heart development and leads to embryonic lethality in Cdk2(-/-)Cdk4(-/- )mutants. We also discuss the specific functions of Cdk4 and Cdk6, which ironically do not compensate for each other

Cdk2 is critical for proliferation and self-renewal of neural progenitor cells in the adult subventricular zone

We investigated the function of cyclin-dependent kinase 2 (Cdk2) in neural progenitor cells during postnatal development. Chondroitin sulfate proteoglycan (NG2)–expressing progenitor cells of the subventricular zone (SVZ) show no significant difference in density and proliferation between Cdk2−/− and wild-type mice at perinatal ages and are reduced only in adult Cdk2−/− mice. Adult Cdk2−/− SVZ cells in culture display decreased self-renewal capacity and enhanced differentiation. Compensatory mechanisms in perinatal Cdk2−/− SVZ cells, which persist until postnatal day 15, involve increased Cdk4 expression that results in retinoblastoma protein inactivation. A subsequent decline in Cdk4 activity to wild-type levels in postnatal day 28 Cdk2−/− cells coincides with lower NG2+ proliferation and self-renewal capacity similar to adult levels. Cdk4 silencing in perinatal Cdk2−/− SVZ cells abolishes Cdk4 up-regulation and reduces cell proliferation and self- renewal to adult levels. Conversely, Cdk4 overexpression in adult SVZ cells restores proliferative capacity to wild-type levels. Thus, although Cdk2 is functionally redundant in perinatal SVZ, it is important for adult progenitor cell proliferation and self-renewal through age-dependent regulation of Cdk4

Mitochondrial degeneration and not apoptosis is the primary cause of embryonic lethality in ceramide transfer protein mutant mice

Ceramide transfer protein (CERT) functions in the transfer of ceramide from the endoplasmic reticulum (ER) to the Golgi. In this study, we show that CERT is an essential gene for mouse development and embryonic survival and, quite strikingly, is critical for mitochondrial integrity. CERT mutant embryos accumulate ceramide in the ER but also mislocalize ceramide to the mitochondria, compromising their function. Cells in mutant embryos show abnormal dilation of the ER and degenerating mitochondria. These subcellular changes manifest as heart defects and cause severely compromised cardiac function and embryonic death around embryonic day 11.5. In spite of ceramide accumulation, CERT mutant mice do not die as a result of enhanced apoptosis. Instead, cell proliferation is impaired, and expression levels of cell cycle–associated proteins are altered. Individual cells survive, perhaps because cell survival mechanisms are activated. Thus, global compromise of ER and mitochondrial integrity caused by ceramide accumulation in CERT mutant mice primarily affects organogenesis rather than causing cell death via apoptotic pathways

Etudes des relations des protéines BTG/APRO avec leurs partenaires CAF1 et PRMT1

LYON1-BU Santé (693882101) / SudocPARIS-BIUM (751062103) / SudocPARIS-BIUP (751062107) / SudocSudocFranceF

Zirconium(IV)-catalysed hydrosilylation of organic carbonates and polycarbonates household wastes into alcohol derivatives.

The Schwartz’s reagent Cp2Zr(H)Cl is a well known stoichiometric reagent for the reduction of unsaturated organic molecules but it has rarely been used in catalytic transformations. Herein, we describe the reduction of a variety of organic carbonates using the catalyst Cp2Zr(H)Cl in combination with Me(MeO)2SiH (DMMS) as reductant. This method was further applied to the reductive depolymerization of some polycarbonate materials and yielded sylilated alcohols and diols in mild conditions. A significant advantage of this recycling method of polycarbonates is its stability towards the additives contained in household plastics and its ability to selectively depolymerize polycarbonate in a mixture containing a polyester and a polycarbonate. Experimental investigations brought evidences on a mechanism based on the hydrozirconation of the carbonyl fragment, thermal σ C–O bond cleavage, and Zr–OR/Si–H σ-bond metathesis reactions to regenerate the hydride catalyst

In search of a function for the TIS21/PC3/BTG1/TOB family

International audienc

Rb/Cdk2/Cdk4 triple mutant mice elicit an alternative mechanism for regulation of the G1/S transition

The G(1)/S-phase transition is a well-toned switch in the mammalian cell cycle. Cdk2, Cdk4, and the rate-limiting tumor suppressor retinoblastoma protein (Rb) have been studied in separate animal models, but interactions between the kinases and Rb in vivo have yet to be investigated. To further dissect the regulation of the G(1) to S-phase progression, we generated Cdk2(-/-)Cdk4(-/-)Rb(-/-) (TKO) mutant mice. TKO mice died at midgestation with major defects in the circulatory systems and displayed combined phenotypes of Rb(-/-) and Cdk2(-/-)Cdk4(-/-) mutants. However, TKO mouse embryonic fibroblasts were not only resistant to senescence and became immortal but displayed enhanced S-phase entry and proliferation rates similar to wild type. These effects were more remarkable in hypoxic compared with normoxic conditions. Interestingly, depletion of the pocket proteins by HPV-E7 or p107/p130 shRNA in the absence of Cdk2/Cdk4 elicited a mechanism for the G(1)/S regulation with increased levels of p27(Kip1) binding to Cdk1/cyclin E complexes. Our work indicates that the G(1)/S transition can be controlled in different ways depending on the situation, resembling a regulatory network

Cdk2 and Cdk4 Activities Are Dispensable for Tumorigenesis Caused by the Loss of p53▿

The loss of p53 induces spontaneous tumors in mice, and p53 mutations are found in approximately 50% of human tumors. These tumors are generally caused by a number of events, including genomic instability, checkpoint defects, mitotic defects, deregulation of transcriptional targets, impaired apoptosis, and G1 deregulation or a combination of these effects. In order to determine the role of proteins involved in G1 control in tumorigenesis, we focused on Cdk2 and Cdk4, two cyclin-dependent kinases that in association with cyclin E and cyclin D promote the G1/S phase transition. We analyzed the consequence of loss of Cdk2 in p53-null animals by generating Cdk2−/− p53−/− mice. These mice are viable and developed spontaneous tumors, predominantly lymphoblastic lymphomas, similar to p53−/− mice. In contrast, the genotypes Cdk4−/− p53−/− were mostly lethal, with few exceptions, and Cdk2−/− Cdk4−/−p53−/− mice die during embryogenesis at embryonic day 13.5. To study the oncogenic potential, we generated mouse embryonic fibroblasts (MEFs) and found that p53−/−, Cdk2−/− p53−/−, Cdk4−/− p53−/−, and Cdk2−/− Cdk4−/− p53−/− MEFs grew at similar rates without entering senescence. Ras-transformed MEFs of these genotypes were able to form colonies in vitro and induce tumors in nude mice. Our results suggest that tumorigenicity mediated by p53 loss does not require either Cdk2 or Cdk4, which necessitates considering the use of broad-spectrum cell cycle inhibitors as a means of effective anti-Cdk cancer therapy