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D Beach

Publications and source records attributed to D Beach.

At least 73 records · Page 4Linked to original sources
PubMed1994

KAP: a dual specificity phosphatase that interacts with cyclin-dependent kinases.

The cyclin-dependent kinases are key cell cycle regulators whose activation is required for passage from one cell cycle phase to the next. In mammalian cells, CDK2 has been implicated in control of the G1 and S phases. We have used a two-hybrid protein interaction screen to identify cDNAs encoding proteins that can interact with CDK2. Among those identified was a protein (KAP), which contained the HCXX-XXGR motif characteristic of protein tyrosine phosphatases. KAP showed phosphatase activity toward substrates containing either phosphotyrosine or phosphoserine residues. Since KAP is not significantly similar to known phosphatases beyond the catalytic core motif, it represents an additional class of dual specificity phosphatase. KAP interacted with cdc2 and CDK2 in yeast. In mammalian cells, KAP also associated with cdc2 and CDK2 but showed a preference for cdc2. The ability of KAP to bind multiple cyclin-dependent kinases suggests that it may play a role in cell cycle regulation.

Amino Acid Sequence↗
PubMed1994

cdt1 is an essential target of the Cdc10/Sct1 transcription factor: requirement for DNA replication and inhibition of mitosis.

We have used an immunoprecipitation-PCR cycle to isolate physically genomic DNA sequences that are bound by the fission yeast cdc10 gene product in an attempt to identify novel target genes. An essential gene, cdt1, has been isolated whose expression is cell cycle regulated in a cdc10 dependent manner. The cdt1 promoter contains a recognition site for a sequence specific DNA binding factor. The cdc10 gene product is a component of this factor. Ectopic expression of cdt1 can complement a temperature sensitive mutation of cdc10 at semipermissive temperature. Cells carrying a null allele of cdt1 are defective in DNA replication but initiate mitotic events, suggesting that cdt1 is essential for the normal dependency relationship of S-phase and mitosis.

Amino Acid Sequence↗
PubMed1994

Interaction between the Cig1 and Cig2 B-type cyclins in the fission yeast cell cycle.

In this report, we describe the cloning and characterization of a B-type cyclin, Cig2 from the fission yeast Schizosaccharomyces pombe. The cig2 gene encodes a 45-kDa protein that is most similar to a previously identified B-type cyclin in S. pombe, Cdc13. Deletion of cig2 had no observable effect on cell viability or progression through the cell cycle. Strains carrying the cig2 null allele do, however, exhibit an enhanced ability to undergo conjugation relative to a wild-type strain. The cig2 transcript was found to undergo periodic oscillation during the cell cycle, peaking at the G1/S-phase boundary. We have investigated the relationship between Cig2 and the other B-type cyclins, Cig1 and Cdc13, in the fission yeast. We found that cells carrying disruptions of both the cig1 and cig2 genes contain multiple nuclei with a 1C DNA content, suggesting that they are delayed in progression through the G1 phase of the cell cycle. The phenotype of this double mutant suggests that there is a delay in septum formation, possibly as a result of defective nuclear separation.

Amino Acid Sequence↗
PubMed1994

Repression of cyclin D1: a novel function of MYC.

Constitutive expression of human MYC represses mRNA levels of cyclin D1 in proliferating BALB/c-3T3 fibroblasts. We expressed a series of mutant alleles of MYC and found that downregulation of cyclin D1 is distinct from previously described properties of MYC. In particular, we found that association with Max is not required for repression of cyclin D1 by MYC in vivo. Conversely, the integrity of a small amino-terminal region (amino acids 92 to 106) of MYC is critical for repression of cyclin D1 but dispensable for transformation of established RAT1A cells. Runoff transcription assays showed that repression occurs at the level of transcription initiation. We cloned the promoter of the gene for human cyclin D1 and found that it lacks a canonical TATA element. Transcription starts at an initiator element similar to that of the adenovirus major late promoter; this element can be directly bound by USF in vitro. Expression of MYC represses the cyclin D1 promoter via core promoter elements and antagonizes USF-mediated transactivation. Taken together, our data define a new pathway for gene regulation by MYC and show that the cyclin D1 gene is a target gene for repression by MYC.

3T3 Cells↗
PubMed1993

p21 is a universal inhibitor of cyclin kinases.

Deregulation of cell proliferation is a hallmark of neoplastic transformation. Alteration in growth control pathways must translate into changes in the cell-cycle regulatory machinery, but the mechanism by which this occurs is largely unknown. Compared with normal human fibroblasts, cells transformed with a variety of viral oncoproteins show striking changes in the subunit composition of the cyclin-dependent kinases (CDKs). In normal cells, CDKs exist predominantly in multiple quaternary complexes, each containing a CDK, cyclin, proliferating cell nuclear antigen and the p21 protein. However, in many transformed cells, proliferating cell nuclear antigen and p21 are lost from these multiprotein enzymes. Here we have investigated the significance of this phenomenon by molecular cloning of p21 and in vitro reconstitution of the quaternary cell-cycle kinase complexes. We find that p21 inhibits the activity of each member of the cyclin/CDK family. Furthermore, overexpression of p21 inhibits the proliferation of mammalian cells. Our results indicate that p21 may be a universal inhibitor of cyclin kinases.

Amino Acid Sequence↗
PubMed1993

A new regulatory motif in cell-cycle control causing specific inhibition of cyclin D/CDK4.

The division cycle of eukaryotic cells is regulated by a family of protein kinases known as the cyclin-dependent kinases (CDKs). The sequential activation of individual members of this family and their consequent phosphorylation of critical substrates promotes orderly progression through the cell cycle. The complexes formed by CDK4 and the D-type cyclins have been strongly implicated in the control of cell proliferation during the G1 phase. CDK4 exists, in part, as a multi-protein complex with a D-type cyclin, proliferating cell nuclear antigen and a protein, p21 (refs 7-9). CDK4 associates separately with a protein of M(r) 16K, particularly in cells lacking a functional retinoblastoma protein. Here we report the isolation of a human p16 complementary DNA and demonstrate that p16 binds to CDK4 and inhibits the catalytic activity of the CDK4/cyclin D enzymes. p16 seems to act in a regulatory feedback circuit with CDK4, D-type cyclins and retinoblastoma protein.

Amino Acid Sequence↗
PubMed1993

Fission yeast chk1 protein kinase links the rad checkpoint pathway to cdc2.

The dependence of cell-cycle progression on the integrity of the genome has been described as checkpoint control. A number of mutants of the fission yeast Schizosaccharomyces pombe, selected for their sensitivity to DNA damage caused by radiation (rad mutants) or to the DNA synthesis inhibitor hydroxyurea (hus mutants) have been classified as checkpoint mutants because they fail to arrest the cell cycle in response to DNA damage or incompletely replicated DNA. Coupling of the checkpoint pathways that monitor DNA repair and replication to control of the cell cycle is essential. In a search for components that interact with the cell-cycle regulatory kinase p34cdc2, we have identified a novel fission yeast protein kinase homologue which is involved in cell-cycle arrest when DNA damage has occurred or when unligated DNA is present. We have called the gene encoding this protein chk1 for checkpoint kinase. Multiple copies of chk1 partially rescue the ultraviolet sensitivity of rad1-1, a mutant deficient in checkpoint control. Identification of a gene involved in checkpoint control as a rescue of a cdc2 mutant links the rad1-dependent DNA-damage-sensing pathway and p34cdc2 activity.

Amino Acid Sequence↗
PubMed1993

Sct1 functions in partnership with Cdc10 in a transcription complex that activates cell cycle START and inhibits differentiation.

A fission yeast cell cycle START gene has been identified, sct1. Loss of sct1 function results in cell cycle arrest at START and simultaneously in derepression of the mating pathway. sct1 therefore functions both as an essential activator of the mitotic cell cycle and as a repressor of differentiation. p72sct1 shares 36% sequence similarity with p85cdc10. p72sct1 is shown to act in partnership with p85cdc10 in a cell cycle regulatory transcription complex. A single dominant mutation within the putative DNA-binding domain of p72sct1 renders the cell independent of cdc10 function for the execution of START.

Amino Acid Sequence↗
PubMed1993

Characterization of the fission yeast mcs2 cyclin and its associated protein kinase activity.

We have previously described the isolation of mcs2-75, a mutation obtained as an allele-specific suppressor of a dominant allele of cdc2. mcs2 was cloned and determined to be an essential gene, the product of which shares homology with the cyclin family of proteins. In contrast to the behavior of some, but not all cyclins, the mcs2 protein is constant in its abundance and localization throughout the cell cycle. A kinase activity that co-precipitates with mcs2 can be detected when myelin basic protein (MBP) is provided as an exogenous substrate. This kinase activity is constant throughout the cell cycle. mcs2 does not appear to associate with the cdc2 protein kinase or an antigenically related kinase. Finally, a protein kinase termed csk1 (cyclin suppressing kinase) was isolated as a high copy suppressor of an mcs2 mutation. csk1 is not essential, however, the level of kinase activity that co-precipitates with mcs2 is reduced approximately 3-fold in strains harboring a csk1 null allele. Therefore, csk1 may encode a protein kinase physically associated with mcs2 or alternatively may function as an upstream activator of the mcs2-associated kinase.

Amino Acid Sequence↗
PubMed1993

Interaction of the pim1/spi1 mitotic checkpoint with a protein phosphatase.

Loss of p58pim1, a homolog of human RCC1, results in uncoupling of mitosis from the completion of DNA replication in fission yeast. An extragenic suppressor of a mutant allele of pim1, esp1, has been isolated and characterized. esp1 encodes a predicted product of 305 amino acid residues, which shares 71% identity with budding yeast SIT4, a type2A related protein phosphatase. p58pim1 binds p25spi1, a 25-kd ras-related GTPase previously isolated as a high dosage suppressor of pim1. The complex dissociates in the presence of guanine nucleotides and Mg2+. The mutant p58pim1 is defective in its ability to bind p25spi1, suggesting that the physical interaction is essential for the maintenance of the interdependency of cell cycle event. In the esp1 pim1 double mutant, the mutant p58pim1 protein is still defective in its ability to bind to p25spi1. However, pmi1 induced premature mitosis is completely suppressed, suggesting that esp1 may act downstream of the p58pim1/p25spi1 physical interaction but upstream of the activation of the M-phase specific histone H1 kinase.

Amino Acid Sequence↗
PubMed1993

Proliferating cell nuclear antigen and p21 are components of multiple cell cycle kinase complexes.

We have recently shown that two proteins, proliferating cell nuclear antigen (PCNA) and p21, are associated with cyclin D. Here we show that PCNA and p21 are common components of a wide variety of cyclin/cyclin-dependent kinase complexes in nontransformed cells. These include kinase complexes containing cyclin A, cyclin B, and cyclin D, associated either with CDC2, CDK2, CDK4, or CDK5. We show that PCNA and p21 form separate quaternary complex with each cyclin/CDK and that these quaternary complexes contain a substantial, if not major, fraction of the cell cycle kinases in asynchronously growing cells. These results suggest that PCNA and p21 may perform a common function for all these kinases.

Animals↗
PubMed1993

Isolation of the Rb-related p130 through its interaction with CDK2 and cyclins.

A two-hybrid protein interaction screen was used to isolate cDNAs encoding human proteins that can interact with human CDK2 in yeast. A new member of the retinoblastoma susceptibility gene family, Rbr-2 (Rb-related), was obtained. The sequence of the Rbr-2 protein shares approximately 50% identify with p107 and homology to Rb within the pocket domain. Several lines of evidence indicate that Rbr-2 is the adenovirus E1A-associated p130. Like Rb and p107, p130Rbr-2 can bind to viral oncoproteins, SV40 large T antigen, and adenovirus E1A through its pocket domain. Although p130Rbr-2 does not bind to CDK2 in vitro, it can interact with cyclins, with a clear preference for D-type cyclins. Because both CDK2 and p130Rbr-2 show affinity for cyclins, we suggest that p130Rbr-2 and CDK2 interacted through a yeast-derived cyclin bridge in the two-hybrid screen. The gene encoding p130Rbr-2 mapped to 16q13, a region of frequent genomic alteration in human tumors.

Adenovirus E1A Proteins↗
PubMed1993

Subunit rearrangement of the cyclin-dependent kinases is associated with cellular transformation.

In normal human diploid fibroblasts, cyclins of the A, B, and D classes each associate with cyclin-dependent kinases (CDKs), proliferating cell nuclear antigen (PCNA), and p21, thereby forming multiple independent quaternary complexes. Upon transformation of diploid fibroblasts with the DNA tumor virus SV40, or its transforming tumor antigen (T), the cyclin D/p21/CDK/PCNA complexes are disrupted. In transformed cells, CDK4 totally dissociates from cyclin D, PCNA, and p21 and, instead, associates exclusively with a polypeptide of 16 kD (p16). Quaternary complexes containing cyclins A or B1 and p21/CDK/PCNA also undergo subunit rearrangement in transformed cells. Both PCNA and p21 are no longer associated with CDC2-cyclin B1 binary complexes. Cyclin A complexes no longer contain p21, and a new 19-kD polypeptide (p19) is found in association with cyclin A. The pattern of subunit rearrangement of cyclin-CDK complexes in SV40-transformed cells is also shared in those containing adeno- or papilloma viral oncoproteins. Rearrangement also occurs in p53-deficient cells derived from Li-Fraumeni patients that carry no known DNA tumor virus. These findings suggest a mechanism by which oncogenic proteins alter the cell cycle of transformed cells.

Amino Acid Sequence↗
PubMed1993

Identification of seven new cut genes involved in Schizosaccharomyces pombe mitosis.

Fission yeast cut mutants cause cytokinesis in the absence of normal nuclear division. These mutants show abnormal uncoupled mitosis and are known to be the result of mutations in the genes encoding DNA topoisomerase II, proteins related to spindle pole duplication, and a kinesin-related mitotic motor. We have screened 717 temperature-sensitive (ts) mutants by individually observing their cytological phenotypes at the restrictive temperature, and have newly isolated 25 cut mutants. Genetic analyses indicate that 14 of them fall into five previously identified loci, namely, top2, cut1, cut5, cut7 and cut9, whereas nine have been mapped onto seven new loci, designated cut13 to cut19. The cytological phenotypes of the newly identified cut mutants can be classified into three groups. One group consists of mutants in which a portion of the nuclear chromatin is stretched by the elongated spindle but the entire nucleus is not separated, reminiscent of, but not identical to, the phenotypes of top2 and cut1; mutants cut14-208, cut15-85, cut16-267 and cut17-275 display such a phenotype. Another group exhibits non-disjunctioned and condensed chromosomes in the presence of the spindle; cut13-131 belongs to this group. The cut19-708 mutant has also been found to have condensed chromosomes. The remaining group has a mixed phenotype of the above two groups; namely, stretched chromatin and condensed chromosomes; cut18-447 exhibits such a phenotype. The isolation and characterization of the mutated genes will be the subjects of future investigations.

Cell Division↗
PubMed1992

D type cyclins associate with multiple protein kinases and the DNA replication and repair factor PCNA.

Human cyclin D1 has been associated with a wide variety of proliferative diseases but its biochemical role is unknown. In diploid fibroblasts we find that cyclin D1 is complexed with many other cellular proteins. Among them are protein kinase catalytic subunits CDK2, CDK4 (previously called PSK-J3), and CDK5 (also called PSSALRE). In addition, polypeptides of 21 kd and 36 kd are identified in association with cyclin D1. We show that the 36 kd protein is the proliferating cell nuclear antigen, PCNA. Cyclin D3 also associates with multiple protein kinases, p21 and PCNA. It is proposed that there exists a quaternary complex of D cyclin, CDK, PCNA, and p21 and that many combinatorial variations (cyclin D1, D3, CDK2, 4, and 5) may assemble in vivo. These findings link a human putative G1 cyclin that is associated with oncogenesis with a well-characterized DNA replication and repair factor.

Amino Acid Sequence↗
PubMed1992

Growth-regulated expression of D-type cyclin genes in human diploid fibroblasts.

The human CCND1 cyclin D1/PRAD1 gene was previously identified by a genetic screen for G1 cyclin function in Saccharomyces cerevisiae and also was identified as the putative BCL1 oncogene. However, its role in human cell proliferation is not known. To determine if expression of human D-type cyclin genes correlates with the state of cell growth, we examined the level of mRNAs for CCND1 and a related gene, CCND3, in normal human diploid fibroblasts (HDF). The levels of both mRNAs decrease upon serum depletion or at high cell densities. Following stimulation of quiescent fibroblasts with serum, the mRNA levels increase gradually to a peak at about 12 hr, prior to the onset of S phase. Induction of cyclin gene expression by serum is reduced concomitantly with the decline in FOS induction in aging HDFs, suggesting a possible relationship to the decrease in the proliferative response to mitogens during cellular senescence. Cycloheximide partially blocks the induction of CCND1 and CCND3 gene expression by serum, suggesting that both de novo protein synthesis-dependent and -independent pathways contribute to induction. Treatment of HDFs with defined growth factors suggests a correlation between CCND mRNA induction and DNA synthesis. However, induction of these genes is not sufficient for the transition from quiescence through G1 into S phase.

Blood↗