title: Role of caspase 9 in activation of HTLV-1 LTR expression by DNA damaging agents.
abstract: Adult T-cell leukemia (ATL) is caused by HTLV-I. The viral Tax oncoprotein plays a central role in initiating the process to ATL. However, after infection HTLV-1 enters into latency, during which virus gene expression is very low, so that the level of Tax is likely insufficient for exerting its oncogenic activities. Therefore only 5% of the infected individuals may develop ATL several decades after infection. It is assumed that the transition from latency to ATL development requires at least a temporary activation of the latent virus in order to elevate Tax to its oncogenic threshold. We have previously found that DNA damaging agents, which usually induce apoptosis, can also activate the viral LTR and that the anti apoptosis Bcl-2 protein not only avoid their apoptosis induction but concomitantly prevents their LTR activation effect. Therefore, the present study was designed to identify the factor that while participating in the apoptotic cascade acts also to activate the viral LTR. For this purpose we employed ectopic vectors expressing these apoptotic factors together with potent shRNAs against each of them and anti caspase peptide inhibitors. We have found that in addition to its function as initiator of the mitochondrial apoptotic cascade, caspase 9 can acts also as an executer which among other non-apoptotic functions it forms an Sp1-p53 complex that activates the LTR by binding to an Sp1 recognition site residing in the LTR. This finding can help in designing effective preventing strategies against ATL development in clinically latent HTLV-1 carriers.
authors.affiliation: Shraga Segal Department of Microbiology and Immunology, Ben Gurion University of the Negev, Beer Sheva, Israel.
authors.forename: Ammar
authors.initials: A
authors.lastname: Abou-Kandil
authors.forename: Rachel
authors.initials: R
authors.lastname: Chamias
authors.forename: Mahmoud
authors.initials: M
authors.lastname: Huleihel
authors.forename: W T
authors.initials: WT
authors.lastname: Godbey
authors.forename: Mordechai
authors.initials: M
authors.lastname: Aboud
mesh_terms: D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology; D000818:Animals; D017209:Apoptosis; D053143:Caspase 2 / Q000235:genetics / Q000378:metabolism; D053453:Caspase 9 / Q000378:metabolism*; D061945:Caspase Inhibitors; D002460:Cell Line; D004247:DNA / Q000378:metabolism*; D004249:DNA Damage; D005786:Gene Expression Regulation; D016356:Gene Products, tax / Q000378:metabolism; D015368:Human T-lymphotropic virus 1 / Q000235:genetics*; D006801:Humans; D051379:Mice; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D034622:RNA Interference; D034741:RNA, Small Interfering; D016329:Sp1 Transcription Factor / Q000378:metabolism; D020079:Terminal Repeat Sequences / Q000235:genetics; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism; D014775:Virus Activation; D051028:bcl-2-Associated X Protein / Q000378:metabolism
chemical_list: D000590:Amino Acid Chloromethyl Ketones; D061945:Caspase Inhibitors; D016356:Gene Products, tax; D019253:Proto-Oncogene Proteins c-bcl-2; D034741:RNA, Small Interfering; D016329:Sp1 Transcription Factor; D016159:Tumor Suppressor Protein p53; D051028:bcl-2-Associated X Protein; C096713:benzyloxycarbonylvalyl-alanyl-aspartyl fluoromethyl ketone; D004247:DNA; D053143:Caspase 2; D053453:Caspase 9