title: Overexpression of p21(waf1) in human T-cell lymphotropic virus type 1-infected cells and its association with cyclin A/cdk2.
abstract: Human T-cell lymphotropic virus type 1 (HTLV-1) is associated with adult T-cell leukemia (ATL) and HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). T-cell transformation is mainly due to the actions of the viral phosphoprotein Tax. Tax interacts with multiple transcriptional factors, aiding the transcription of many cellular genes. Here, we report that the cyclin-dependent kinase inhibitor p21/waf1 is overexpressed in all HTLV-1-infected cell lines tested as well as in ATL and HAM/TSP patient samples. Tax was found to be able to transactivate the endogenous p21/waf1 promoter, as detected by RNase protection, as well as activate a series of wild-type and 5'-deletion constructs linked to a luciferase reporter cassette. Wild-type but not a mutant form of Tax (M47) transactivated the p21/waf1 promoter in a p53-independent manner and utilized a minimal promoter that contained E2A and TATA box sequences. The p21/waf1 protein was reproducibly observed to be complexed with cyclin A/cdk2 and not with any other known G(1), S, or G(2)/M cyclins. Functionally, the association of p21/cyclin A/cdk2 decreased histone H1 phosphorylation in vitro, as observed in immunoprecipitations followed by kinase assays, and affected other substrates, such as the C terminus of Rb protein involved in c-Abl and histone deacetylase-1 (HDAC1) regulation. Interestingly, upon the use of a stress signal, such as gamma-irradiation, we found that the p21/cyclin A/cdk2 complex was able to block all known phosphorylation sites on the Rb molecule. Finally, using elutriated cell cycle fractions and a stress signal, we observed that the HTLV-1-infected T cells containing wild-type Tax, which had been in early or mid-G(1) phase prior to gamma-irradiation, arrested in G(1) and did not undergo apoptosis. This may be an important mechanism for an oncogenic virus such as HTLV-1 to stop the host at the G(1)/S boundary and to repair the damaged DNA upon injury, prior to S-phase entry.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Medicine and Dentistry of New Jersey, New Jersey Medical School, Newark, New Jersey 07103, USA.
authors.forename: C
authors.initials: C
authors.lastname: de La Fuente
authors.forename: F
authors.initials: F
authors.lastname: Santiago
authors.forename: S Y
authors.initials: SY
authors.lastname: Chong
authors.forename: L
authors.initials: L
authors.lastname: Deng
authors.forename: T
authors.initials: T
authors.lastname: Mayhood
authors.forename: P
authors.initials: P
authors.lastname: Fu
authors.forename: D
authors.initials: D
authors.lastname: Stein
authors.forename: T
authors.initials: T
authors.lastname: Denny
authors.forename: F
authors.initials: F
authors.lastname: Coffman
authors.forename: N
authors.initials: N
authors.lastname: Azimi
authors.forename: R
authors.initials: R
authors.lastname: Mahieux
authors.forename: F
authors.initials: F
authors.lastname: Kashanchi
mesh_terms: D000818:Animals; D042846:CDC2-CDC28 Kinases; D019925:Cyclin A / Q000378:metabolism*; D051357:Cyclin-Dependent Kinase 2; D050759:Cyclin-Dependent Kinase Inhibitor p21; D018844:Cyclin-Dependent Kinases / Q000378:metabolism*; D016213:Cyclins / Q000378:metabolism*; D005720:Gamma Rays; D016356:Gene Products, tax / Q000378:metabolism; D015490:HTLV-I Infections / Q000821:virology; D015368:Human T-lymphotropic virus 1 / Q000378:metabolism*; D006801:Humans; D015459:Leukemia-Lymphoma, Adult T-Cell / Q000821:virology; D051379:Mice; D015493:Paraparesis, Tropical Spastic / Q000821:virology; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D016160:Retinoblastoma Protein / Q000378:metabolism; D013601:T-Lymphocytes / Q000821:virology*; D014407:Tumor Cells, Cultured
chemical_list: C493956:CDKN1A protein, human; C493957:Cdkn1a protein, mouse; D019925:Cyclin A; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D016356:Gene Products, tax; D016160:Retinoblastoma Protein; D017346:Protein Serine-Threonine Kinases; D042846:CDC2-CDC28 Kinases; C495894:CDK2 protein, human; C495893:Cdk2 protein, mouse; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases