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Larochelle S, Batliner J, Gamble MJ, Barboza NM, Kraybill BC, Blethrow JD, Shokat KM, Fisher RP. Dichotomous but stringent substrate selection by the dual-function Cdk7 complex revealed by chemical genetics. Nat Struct Mol Biol 2005; 13:55-62. [PMID: 16327805 DOI: 10.1038/nsmb1028] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2005] [Accepted: 10/26/2005] [Indexed: 02/04/2023]
Abstract
Cdk7 performs two essential but distinct functions as a CDK-activating kinase (CAK) required for cell-cycle progression and as the RNA polymerase II (Pol II) CTD kinase of general transcription factor IIH. To investigate the substrate specificity underlying this dual function, we created an analog-sensitive (AS) Cdk7 able to use bulky ATP derivatives. Cdk7-AS-cyclin H-Mat1 phosphorylates approximately 10-15 endogenous polypeptides in nuclear extracts. We identify seven of these as known and previously unknown Cdk7 substrates that define two classes: proteins such as Pol II and transcription elongation factor Spt5, recognized efficiently only by the fully activated Cdk7 complex, through sequences surrounding the site of phosphorylation; and CDKs, targeted equivalently by all active forms of Cdk7, dependent on substrate motifs remote from the phosphoacceptor residue. Thus, Cdk7 accomplishes dual functions in cell-cycle control and transcription not through promiscuity but through distinct, stringent modes of substrate recognition.
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Affiliation(s)
- Stéphane Larochelle
- Molecular Biology Program, Memorial Sloan-Kettering Cancer Center, 1275 York Avenue, New York, New York 10021, USA
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2
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Lee M, O'Regan S, Moreau JL, Johnson AL, Johnston LH, Goding CR. Regulation of the Pcl7-Pho85 cyclin-cdk complex by Pho81. Mol Microbiol 2000; 38:411-22. [PMID: 11069666 DOI: 10.1046/j.1365-2958.2000.02140.x] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Saccharomyces cerevisiae strains lacking a functional Pho85 cyclin-dependent kinase (cdk) exhibit a complex phenotype, including deregulation of phosphatase genes controlled by the transcription factor Pho4, slow growth on rich media, failure to grow using galactose, lactate or glycerol as a carbon source and hyperaccumulation of glycogen. The ability of Pho85 to regulate the transcription factor Pho4 is mediated by its association the Pho80 cyclin. Some other regulatory functions of the Pho85 cdk have been shown to be mediated via its interaction with a recently identified family of Pho80-related cyclins (Pcls). Here, we show that the poorly characterized Pho80-like protein Pcl7 forms a functional kinase complex with the Pho85 cdk, and that the activity of this complex is inhibited in response to phosphate starvation. Additionally, we show that Pcl7 interacts with the phosphate-regulated cyclin-cdk inhibitor Pho81, and that the regulation of the Pcl7-Pho85 complex in response to changes in phosphate levels is dependent on Pho81. Thus, we demonstrate for the first time that the Pho81 regulator is not dedicated to regulating Pho80, but may act to co-ordinate the activity of both the Pho80-Pho85 and Pcl7-Pho85 cyclin-cdk complexes in response to phosphate levels. We also demonstrate that expression of Pcl7 is cell cycle regulated, with maximal activity occurring in mid to late S-phase, perhaps suggesting a role for Pcl7 in cell cycle progression. Finally, we describe the phenotype of pcl7Delta and pcl6Delta yeast strains that have defects in carbon source utilization.
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Affiliation(s)
- M Lee
- Eukaryotic Transcription Laboratory, Marie Curie Research Institute, The Chart, Oxted, Surrey RH8 OTL, UK
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3
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Persson BL, Petersson J, Fristedt U, Weinander R, Berhe A, Pattison J. Phosphate permeases of Saccharomyces cerevisiae: structure, function and regulation. BIOCHIMICA ET BIOPHYSICA ACTA 1999; 1422:255-72. [PMID: 10548719 DOI: 10.1016/s0304-4157(99)00010-6] [Citation(s) in RCA: 66] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Affiliation(s)
- B L Persson
- Department of Engineering, Växjö University, S-351 95, Växjö, Sweden.
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4
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Wilson WA, Mahrenholz AM, Roach PJ. Substrate targeting of the yeast cyclin-dependent kinase Pho85p by the cyclin Pcl10p. Mol Cell Biol 1999; 19:7020-30. [PMID: 10490639 PMCID: PMC84697 DOI: 10.1128/mcb.19.10.7020] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/1999] [Accepted: 07/26/1999] [Indexed: 11/20/2022] Open
Abstract
In Saccharomyces cerevisiae, PHO85 encodes a cyclin-dependent protein kinase (Cdk) catalytic subunit with multiple regulatory roles thought to be specified by association with different cyclin partners (Pcls). Pcl10p is one of four Pcls with little sequence similarity to cyclins involved in cell cycle control. It has been implicated in specifying the phosphorylation of glycogen synthase (Gsy2p). We report that recombinant Pho85p and Pcl10p produced in Escherichia coli reconstitute an active Gsy2p kinase in vitro. Gsy2p phosphorylation required Pcl10p, occurred at physiologically relevant sites, and resulted in inactivation of Gsy2p. The activity of the reconstituted enzyme was even greater than Pho85p-Pcl10p isolated from yeast, and we conclude that, unlike many Cdks, Pho85p does not require phosphorylation for activity. Pcl10p formed complexes with Gsy2p, as judged by (i) gel filtration of recombinant Pcl10p and Gsy2p, (ii) coimmunoprecipitation from yeast cell lysates, and (iii) enzyme kinetic behavior consistent with Pcl10p binding the substrate. Synthetic peptides modeled on the sequences of known Pho85p sites were poor substrates with high K(m) values, and we propose that Pcl10p-Gsy2p interaction is important for substrate selection. Gel filtration of yeast cell lysates demonstrated that most Pho85p was present as a monomer, although a portion coeluted in high-molecular-weight fractions with Pcl10p and Gsy2p. Overexpression of Pcl10p sequestered most of the Pho85p into association with Pcl10p. We suggest a model for Pho85p function in the cell whereby cyclins like Pcl10p recruit Pho85p from a pool of monomers, both activating the kinase and targeting it to substrate.
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Affiliation(s)
- W A Wilson
- Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, Indiana 46202, USA
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5
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Michalides RJ. Cell cycle regulators: mechanisms and their role in aetiology, prognosis, and treatment of cancer. J Clin Pathol 1999; 52:555-68. [PMID: 10645224 PMCID: PMC500945 DOI: 10.1136/jcp.52.8.555] [Citation(s) in RCA: 73] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Affiliation(s)
- R J Michalides
- Division of Tumour Biology, The Netherlands Cancer Institute, Amsterdam, Netherlands.
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6
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Lam MH, House CM, Tiganis T, Mitchelhill KI, Sarcevic B, Cures A, Ramsay R, Kemp BE, Martin TJ, Gillespie MT. Phosphorylation at the cyclin-dependent kinases site (Thr85) of parathyroid hormone-related protein negatively regulates its nuclear localization. J Biol Chem 1999; 274:18559-66. [PMID: 10373465 DOI: 10.1074/jbc.274.26.18559] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Parathyroid hormone-related protein (PTHrP) is expressed by a wide variety of cells and is considered to act as a secreted factor; however, evidence is accumulating for it to act in an intracrine manner. We have determined that PTHrP localizes to the nucleus at the G1 phase of the cell cycle and is transported to the cytoplasm when cells divide. PTHrP contains a putative nuclear localization sequence (NLS) (residues 61-94) similar to that of SV40 T-antigen, which may be implicated in the nuclear import of the molecule. We identified that Thr85 immediately prior to the NLS of PTHrP was phosphorylated by CDC2-CDK2 and phosphorylation was cell cycle-dependent. Mutation of Thr85 to Ala85 resulted in nuclear accumulation of PTHrP, while mutation to Glu85 to mimic a phosphorylated residue resulted in localization of PTHrP to the cytoplasm. Combined, the data demonstrate that the intracellular localization of PTHrP is phosphorylation- and cell cycle-dependent, and such control further supports a potential intracellular role (10,34,35) for PTHrP.
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Affiliation(s)
- M H Lam
- St. Vincent's Institute of Medical Research and the Department of Medicine, The University of Melbourne, 41 Victoria Parade, Fitzroy, Victoria 3065, Australia
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7
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Tennyson CN, Lee J, Andrews BJ. A role for the Pcl9-Pho85 cyclin-cdk complex at the M/G1 boundary in Saccharomyces cerevisiae. Mol Microbiol 1998; 28:69-79. [PMID: 9593297 DOI: 10.1046/j.1365-2958.1998.00773.x] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
PHO85 is a cyclin-dependent kinase (CDK) with roles in phosphate and glycogen metabolism and cell cycle progression. As a CDK, Pho85 is activated by association with Pho85 cyclins (Pcls), of which 10 are known. PCL1, PCL2 and PCL9 are the only members of the Pho85 cyclin family that are expressed in a cell cycle-regulated pattern. We found that PCL9 is expressed in late M/early G1 phase of the cell cycle and is activated by the transcription factor, Swi5. This pattern of regulation is different from PCL1 and PCL2, which are expressed later in G1 phase and are regulated primarily by the transcription factor SBF. Co-immunoprecipitation experiments using in vitro translated proteins showed that Pcl9 and Pho85 form a complex. Furthermore, immunoprecipitated Pcl9 complexes from yeast lysates were capable of phosphorylating the exogenous substrate Pho4. The Pcl9-associated kinase activity was dependent on PHO85, showing that Pcl9 and Pho85 form a functionally active kinase complex in vivo. Deletion of PCL9 in diploid cells caused random, rather than bipolar, budding in 18% of cells. In contrast, deletion of PCL2, the closest relative of PCL9, had no effect on the budding pattern. Deleting more members of the PCL1,2 subfamily (which includes PCL9) increased the percentage of random budding in the cell population. When all members of the PCL1,2 subfamily were deleted, 73% of cells budded randomly, a value similar to that obtained when the CDK partner PHO85 was deleted. Our results show that PCL9 and PHO85 form a functional kinase complex and suggest a role for Pho85 CDKs at the M/G1 boundary.
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Affiliation(s)
- C N Tennyson
- Department of Molecular and Medical Genetics, University of Toronto, Canada
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8
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Abstract
We report the isolation and characterization of a protein kinase from the fission yeast Schizosaccharomyces pombe. The proposed Prk1 protein contains 352 amino acids and has significant homology to the Ume5p kinase (also known as Srb10p, Ssn3p and Are1p) of the budding yeast Saccharomyces cerevisiae, a cyclin-dependent kinase involved in regulating the transcription of a diverse set of genes. Disruption of the prk1 gene increases flocculation but does not appear to have any other significant effect on cell behaviour. This defect can be overcome by expressing the UME5 gene, indicating that Prk1 is the fission yeast homologue of Ume5p.
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Affiliation(s)
- P Watson
- Department of Biological Sciences, University of Warwick, Coventry, U.K
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9
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Chellappan SP, Giordano A, Fisher PB. Role of cyclin-dependent kinases and their inhibitors in cellular differentiation and development. Curr Top Microbiol Immunol 1998; 227:57-103. [PMID: 9479826 DOI: 10.1007/978-3-642-71941-7_4] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Affiliation(s)
- S P Chellappan
- Department of Pathology, Herbert Irving Comprehensive Cancer Center, College of Physicians and Surgeons of Columbia University, New York, NY 10032, USA
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10
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Walker DH. Small-molecule inhibitors of cyclin-dependent kinases: molecular tools and potential therapeutics. Curr Top Microbiol Immunol 1998; 227:149-65. [PMID: 9479830 DOI: 10.1007/978-3-642-71941-7_8] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Affiliation(s)
- D H Walker
- Department of Cancer Biology, Glaxo Wellcome, RTP NC 27709, USA
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11
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Abstract
Cyclins are highly conserved proteins that activate cyclin-dependent kinases (CDKs) to regulate the cell cycle, transcription and other cellular processes. The completion of the genome sequence of the budding yeast Saccharomyces cerevisiae allows an appraisal of the functions of the entire complement of cyclins in a eukaryotic organism. The cyclin family of budding yeast is reviewed from a functional perspective with an emphasis on what genetic and biochemical experiments have revealed about cyclin-CDK substrates.
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Affiliation(s)
- B Andrews
- Department of Molecular and Medical Genetics, University of Toronto, Canada.
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12
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Affiliation(s)
- K A Jones
- The Salk Institute for Biological Studies, La Jolla, California 92037-1099 USA.
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13
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Krstic MD, Rogatsky I, Yamamoto KR, Garabedian MJ. Mitogen-activated and cyclin-dependent protein kinases selectively and differentially modulate transcriptional enhancement by the glucocorticoid receptor. Mol Cell Biol 1997; 17:3947-54. [PMID: 9199329 PMCID: PMC232247 DOI: 10.1128/mcb.17.7.3947] [Citation(s) in RCA: 216] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Cyclin-dependent kinase (CDK) and mitogen-activated protein kinase (MAPK) phosphorylate the rat glucocorticoid receptor in vitro at distinct sites that together correspond to the major phosphorylated receptor residues observed in vivo; MAPK phosphorylates receptor residues threonine 171 and serine 246, whereas multiple CDK complexes modify serines 224 and 232. Mutations in these kinases have opposite effects on receptor transcriptional activity in vivo. Receptor-dependent transcriptional enhancement is reduced in yeast strains deficient in the catalytic (p34CDC28) or certain regulatory (cyclin) subunits of CDK complexes and is increased in a strain devoid of the mammalian MAPK homologs FUS3 and KSS1. These findings indicate that the glucocorticoid receptor is a target for multiple kinases in vivo, which either positively or negatively regulate receptor transcriptional enhancement. The control of receptor transcriptional activity via phosphorylation provides an increased array of regulatory inputs that, in addition to steroid hormones, can influence receptor function.
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Affiliation(s)
- M D Krstic
- Biochemistry and Biophysics, University of California, San Francisco, 94143-0445, USA
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14
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Abstract
Neuronal Cdc2-like kinase, Nclk, is a heterodimer of a Cdk5 catalytic subunit and a 25 kDa regulatory subunit derived proteolytically from a neuron- and central nervous system-specific 35 kDa protein. The regulatory subunit is mandatory for kinase activity, hence it is designated the neuronal Cdk5 activator, p25/p35nck5a. Nclk has been suggested to play a regulatory role in neuro-cytoskeleton dynamics and in neuronal differentiation. In addition to the activation by Nck5a, Cdk5 is regulated by other mechanisms including additional activator proteins and inhibition by phosphorylation of specific amino acid residues. While Nclk shares common catalytic and regulatory properties with other members of the cdc2-like kinase family, it also displays unique characteristics that may be important for its neuronal functions.
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Affiliation(s)
- K Y Lee
- Department of Medical Biochemistry, Faculty of Medicine, University of Calgary, Canada
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15
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Kramer KM, Johnston LH. An unwelcome partner: parasitic choreography of the host cell cycle? Trends Microbiol 1997; 5:169-70; discussion 170-1. [PMID: 9160499 DOI: 10.1016/s0966-842x(97)01016-0] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Affiliation(s)
- K M Kramer
- Divn of Yeast Genetics, National Institute for Medical Research, London, UK
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16
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Abstract
The activity of most protein kinases is highly regulated, typically via phosphorylation and/or subunit association. However, the folding of protein kinases into an active state or a form capable of activation is now emerging as another important step through which they can be regulated. The 50-kDa protein Cdc37 and the associated heat-shock protein Hsp90 have been found to bind to, and be required for the activity of, diverse protein kinases, including Cdk4, v-Src, Raf and SEVENLESS. Together, Cdc37 and Hsp90 may act as a general chaperone for protein kinases, in particular those involved in signal-transduction pathways and cell-cycle control.
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Affiliation(s)
- T Hunter
- The Salk Institute for Biological Studies, 10010 North Torrey Pines Road, La Jolla, CA 92037, USA
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17
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Measday V, Moore L, Retnakaran R, Lee J, Donoviel M, Neiman AM, Andrews B. A family of cyclin-like proteins that interact with the Pho85 cyclin-dependent kinase. Mol Cell Biol 1997; 17:1212-23. [PMID: 9032248 PMCID: PMC231846 DOI: 10.1128/mcb.17.3.1212] [Citation(s) in RCA: 153] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
In budding yeast, entry into the mitotic cell cycle, or Start, requires the Cdc28 cyclin-dependent kinase (Cdk) and one of its three associated G1 cyclins, Cln1, Cln2, or Cln3. In addition, two other G1 cyclins, Pcl1 and Pcl2, associate with a second Cdk, Pho85, to contribute to Start. Although Pho85 is not essential for viability, Pcl1,2-Pho85 kinase complexes become essential for Start in the absence of Cln1,2-Cdc28 kinases. In addition, Pho85 interacts with a third cyclin, Pho80, to regulate acid phosphatase gene expression. Other cellular roles for Pho85 cyclin-Cdk complexes are suggested by the multiple phenotypes associated with deletion of PHO85, in addition to Start defects and deregulated acid phosphatase gene expression. Strains with pho80, pcl1, and pcl2 deletions show only a subset of the pho85 mutant phenotypes, suggesting the existence of additional Pho85 cyclins (Pcls). We used two-hybrid screening and database searching to identify seven additional cyclin-related genes that may interact with Pho85. We found that all of the new genes encode proteins that interacted with Pho85 in an affinity chromatography assay. One of these genes, CLG1, was previously suggested to encode a cyclin, based on the protein's sequence homology to Pcl1 and Pcl2. We have named the other genes PCL5, PCL6, PCL7, PCL8, PCL9, and PCL10. On the basis of sequence similarities, the PCLs can be divided into two subfamilies: the Pcl1,2-like subfamily and the Pho80-like subfamily. We found that deletion of members of the Pcl1,2 class of genes resulted in pronounced morphological abnormalities. In addition, we found that expression of one member of the Pcl1,2 subfamily, PCL9, is cell cycle regulated and is decreased in cells arrested in G1 by pheromone treatment. Our studies suggest that Pho85 associates with multiple cyclins and that subsets of cyclins may direct Pho85 to perform distinct roles in cell growth and division.
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Affiliation(s)
- V Measday
- Department of Molecular and Medical Genetics, University of Toronto, Canada
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18
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Poon RY, Lew J, Hunter T. Identification of functional domains in the neuronal Cdk5 activator protein. J Biol Chem 1997; 272:5703-8. [PMID: 9038181 DOI: 10.1074/jbc.272.9.5703] [Citation(s) in RCA: 74] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Cyclin-dependent kinase 5 (Cdk5) is activated by the neuronal-specific activator protein, p35. In contrast to the activation of typical CDKs by cyclin subunits, p35.Cdk5 was not further activated by the CDK-activating kinase (CAK) and was neither phosphorylated nor inhibited by the Tyr-15-specific Wee1 kinase. The previously identified proteolytic active fragment of p35, p25 (residues 91-307) as well as the slightly smaller fragment containing residues 109-291, was found to be sufficient to bind and activate Cdk5. Other CDKs, including Cdk2, associated weakly with p25. However, their kinase activity was only activated to the low level observed for cyclin A.Cdk2 without Thr-160 phosphorylation, and phosphorylation of Thr-160 in Cdk2 did not activate the p25.Cdk2 complex further. We have identified distinct regions in p35 required for binding to Cdk5 or activation of Cdk5. Residues approximately 150-200 of p35 were sufficient for binding to Cdk5, but residues approximately 279-291 were needed in addition for activation of Cdk5 in vitro.
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Affiliation(s)
- R Y Poon
- Salk Institute for Biological Studies, La Jolla, California 92037, USA
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19
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Abstract
The completion of the budding yeast genome sequencing project has made it possible to determine not only the total number of genes, but also the exact number of genes of a particular type 1-3. As a consequence, we now know exactly how many protein kinases are encoded by the yeast genome, a number of considerable interest because of the importance of protein phosphorylation in the control of so many cellular processes.
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Affiliation(s)
- T Hunter
- Salk Institute, La Jolla, CA 92037, USA.
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20
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Poon RY. Generation of phosphorylated cyclin-dependent kinase 2 and functional characterization of threonine-160-specific phosphatase KAP. Methods Enzymol 1997; 283:283-92. [PMID: 9251027 DOI: 10.1016/s0076-6879(97)83023-6] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Affiliation(s)
- R Y Poon
- Department of Biochemistry, Hong Kong University of Science and Technology, Clearwater Bay, Kowloon, Hong Kong
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21
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Sauer K, Weigmann K, Sigrist S, Lehner CF. Novel members of the cdc2-related kinase family in Drosophila: cdk4/6, cdk5, PFTAIRE, and PITSLRE kinase. Mol Biol Cell 1996; 7:1759-69. [PMID: 8930898 PMCID: PMC276024 DOI: 10.1091/mbc.7.11.1759] [Citation(s) in RCA: 54] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
In addition to the previously identified Drosophila cdc2 and cdc2c genes, we have identified four additional cdc2-related genes with low stringency and polymerase chain reaction approaches. Sequence comparisons suggest that the four putative kinases represent the Drosophila homologues of vertebrate cdk4/6, cdk5, PCTAIRE, and PITSLRE kinases. Although the similarity between human and Drosophila homologues is extensive in the case of cdk5, PCTAIRE, and PITSLRE kinases (78%, 58%, and 65% identity in the kinase domain), only limited conservation is observed for Drosophila cdk4/6 (47% identity). However, like vertebrate cdk4 and cdk6, Drosophila cdk4/6 binds also to a D-type cyclin according to the results of two-hybrid experiments in yeast. Northern blot analysis indicated that the four Drosophila kinases are expressed throughout embryogenesis. Expression in early embryogenesis appeared to be ubiquitous according to in situ hybridization. Abundant expression already at the start of embryogenesis and long before neuron differentiation was also observed in the case of cdk5 protein, which has been described as predominantly neuron specific in mice. Sequence conservation and expression pattern, therefore, suggest that all of these kinases perform important cellular functions.
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Affiliation(s)
- K Sauer
- Friedrich-Miescher-Laboratorium, Max-Planck-Gesellschaft, Tübingen, Germany
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22
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Abstract
Cyclin-dependent protein kinases (Cdks) play key roles in regulating cell division and gene expression. Most Cdks require binding of a cyclin and phosphorylation by a Cdk-activating kinase (CAK) to be active. We report the identification of Civ1 (CAK in vivo), a novel CAK activity in S. cerevisiae. Civ1 is most similar in sequence to the Cdks, but unlike them is active as a monomer and may thus be the founding member of a novel family of kinases. Civ1 binds tightly to and phosphorylates Cdc28, thereby allowing its subsequent activation by the binding of a cyclin. The CIV1 gene is essential for yeast cell viability, and Cdc28 phosphorylation and activity are conditionally inhibited in a civ1-4 temperature-sensitive mutant. Civ1 is the only CAK for which there are genetic data indicating that its activity is physiologically relevant in vivo.
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Affiliation(s)
- J Y Thuret
- Service de Biochimie et Génétique Molécularie, Gif-sur-Yvette, France
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23
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Santos JA, Logarinho E, Tapia C, Allende CC, Allende JE, Sunkel CE. The casein kinase 1 alpha gene of Drosophila melanogaster is developmentally regulated and the kinase activity of the protein induced by DNA damage. J Cell Sci 1996; 109 ( Pt 7):1847-56. [PMID: 8832407 DOI: 10.1242/jcs.109.7.1847] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
We report the molecular cloning and characterisation of the first CK1(casein kinase) gene of Drosophila melanogaster (dmCK1). The protein sequence (DMCK1) shares significant homology with other mammalian CK1 protein kinases of the alpha sub-class. The dmCK1 gene is expressed only in adult females and during early embryonic development as a single transcript. Western blot analysis of total protein extracts of different stages of development show that the gene product is likewise present during early embryogenesis and in adult females. Kinase activity studies show that DMCK1 is active when in vitro translated but inactive when immunoprecipitated from total early embryo extracts. However, after dephosphorylation treatment the immunoprecipitates show high kinase activity. More significantly, DMCK1 kinase activity present in the immunoprecipitates can be specifically activated by gamma-irradiation of early embryos. Also, when DMCK1 is immunoprecipitated after irradiation it appears to undergo phosphorylation. Immunolocalization of DMCK1 in early embryos shows that the protein is predominantly cytoplasmic but after irradiation there is a significant relocalization to the interphase nucleus. The results suggest a possible requirement of the Drosophila CK1 alpha for mechanisms associated with DNA repair during early embryogenesis.
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Affiliation(s)
- J A Santos
- Centro de Citologia Experimental da Universidade do Porto, Portugal
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24
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Fang F, Orend G, Watanabe N, Hunter T, Ruoslahti E. Dependence of cyclin E-CDK2 kinase activity on cell anchorage. Science 1996; 271:499-502. [PMID: 8560263 DOI: 10.1126/science.271.5248.499] [Citation(s) in RCA: 301] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Most nonmalignant cells are anchorage-dependent; they require substrate attachment for growth and, in some instances, survival. This requirement is lost on oncogenic transformation. The cyclin E-CDK2 complex, which is required for the G1-S transition of the cell cycle, was activated in late G1 phase in attached human fibroblasts, but not in fibroblasts maintained in suspension. In transformed fibroblasts the complex was active regardless of attachment. The lack of cyclin E-CDK2 activity in suspended cells appeared to result from increased expression of CDK2 inhibitors and a concomitant decrease in phosphorylation of CDK2 on threonine-160. Suppression of cyclin E-CDK2 activity may thus underlie the anchorage dependence of cell growth.
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Affiliation(s)
- F Fang
- La Jolla Cancer Research Foundation, Cancer Center, CA 92037, USA
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