Structure and cell cycle-regulated transcription of the human cyclin A gene.

Abstract

Cyclin A is a cell cycle regulatory protein that functions in mitotic and S-phase control in mammalian somatic cells. Its deregulated expression may have a role in cellular transformation. We have cloned and sequenced the human cyclin A gene and cDNAs representing its mRNAs and have characterized its promoter. Using synchronized cultures of NIH 3T3 cells stably transfected with cyclin A promoter/luciferase constructs, we show that the promoter is repressed during the G, phase of the cell cycle and is activated at S-phase entry. Cell cycle regulation of the cyclin A gene promoter is mediated by sequences extending from -79 to +100 relative to the predominant transcription start site. It does not require the presence of a functional retinoblastoma protein.Cyclins control the transitions between the phases of the eukaryotic cell cycle as regulatory subunits of the cyclindependent kinases (cdk) (1). Phase-specific activation of the cdk is in part regulated by phase-specific expression of their cyclin component. In mammalian somatic cells, the G1 cyclins ofthe D and E type regulate the passage of G1 (2), cyclin A is required for S phase and passage through G2 (3), and the kinase composed of a B-type cyclin and p34cdc2 is the key regulator of mitosis (4). Cyclin A was first identified in sea urchin embryos (5). It can bind and activate the kinases cdc2 and cdk2 (6, 7) and is involved in the control of mitosis and S phase as well. Thus, injection of cyclin A mRNA drives G2-arrested Xenopus oocytes into meiotic metaphase (8), and degradation of the protein is necessary for the exit from mitosis (9). Cyclin A mutant Drosophila embryos undergo cell cycle arrest in G2 (10), and somatic mammalian cells are blocked in G2 upon ablation of cyclin A (11). In addition to its mitotic functions, cyclin A may have a role in the dependence of mitosis on S-phase completion (12). Cyclin A is required for S-phase passage in normal mammalian cells, while cyclin B is not (3,12,13). Cyclin A may indeed be directly involved in DNA replication: it colocalizes with the DNA replication complex (14, 15) and was found in a cellular activity that promotes large tumor-antigen-dependent simian virus 40 DNA replication in Gl-phase cell extracts (16); cyclin A/cdk2 may phosphorylate and activate the cellular DNA replication factor RPA (17, 18). During S phase, cyclin A forms a complex containing cdk2, the pRB-related protein p107, and the transcription factor E2F (19,20). E2F regulates a number of growth-promoting genes (21) and is negatively controlled during G1 by binding to pRB (22). In adenovirus 5-infected cells, the viral ElA oncoprotein dissociates the pRB/E2F complex (23,24) and binds to cyclin A via p107 in S phase (25,26). A possible role for cyclin A in cellular transformation was further suggested by our previous finding of a hepatitis B virus integration in the human cyclin A gene in a primary liver carcinoma (27). In this tumor, cyclin A-specific mRNA is exclusively transcribed from a viral promoter (28), indicating that deregu...

BPV-4 E8 transforms NIH3T3 cells, up-regulates cyclin A and cyclin A-associated kinase activity and de-regulates expression of the cdk inhibitor p27Kip1

“…Cyclin A promoter activity as a measure of p27 Kip1 functional status During the cell cycle, cyclin A gene expression is strictly regulated at the level of transcription (Henglein et al, 1994) and cyclin A-associated kinase activity is rate limiting for entry of mammalian ®broblasts into S-phase (Resnitzky et al, 1994). Also, normal cells maintained in low serum (Firpo et al, 1994) or in suspension (Guadagno et al, 1993;Fang et al, 1996) do not express cyclin A and cannot progress into S-phase.…”

“…D-type cyclins are required for progression through early/mid G1 phase of the cell cycle and in the decision to embark on a new cell cycle or to enter a quiescent state (GO) after mitosis, linking cell exposure to external cues to entry into the cell cycle (Won et al, 1992;Baldin et al, 1993). Cyclin E is expressed in late G1 and is required for entry into Sphase in mammalian ®broblasts (Resnitzky et al, 1994;Ohtsubo et al, 1995), while Cyclin A is ®rst expressed at the G1/S transition (Henglein et al, 1994) and is required, in complex with cdk2, for the completion of S-phase and, in complex with cdc2, for passage through G2 and mitosis (Girard et al, 1991;Pagano et al, 1992).…”

“…Cyclin A gene expression is regulated at the level of transcriptional initiation with expression being repressed in G1 and strongly induced as cells enter Sphase (Henglein et al, 1994). Cyclin E-cdk2 activity is required for elevated cyclin A expression in NIH3T3 cells (Zerfass-Thome et al, 1997).…”

K-ras modulates the cell cycle via both positive and negative regulatory pathways

“…pAluc, which contains the cyclin A promoter linked to the ®re¯y luciferase cDNA (Henglein et al, 1994), was provided by Dr Berthold Henglein (Paris, France). pE2FCAT which contains the E2F-responsive promoter linked to the chloramphenicol transferase (CAT) cDNA (Buck et al, 1995) was provided by Dr Rene Bernards (Amsterdam, The Netherlands).…”

Identification of novel cyclin gene fusion transcripts in endometrioid ovarian carcinomas

“…The expression levels of Cyclin A2 are tightly synchronized with cell cycle progression. CCNA2 transcription begins in late G1, peaks and plateaus in mid‐S, and then declines in G2 23. The transcription is mostly regulated by the transcription factor E2F that derepresses the promoter 24.…”