title: Cell type-specific cleavage of nucleocapsid protein by effector caspases during SARS coronavirus infection.
abstract: The epidemic outbreak of severe acute respiratory syndrome (SARS) in 2003 was caused by a novel coronavirus (CoV), designated SARS-CoV. The RNA genome of SARS-CoV is complexed by the nucleocapsid protein (N) to form a helical nucleocapsid. Besides this primary function, N seems to be involved in apoptotic scenarios. We show that upon infection of Vero E6 cells with SARS-CoV, which elicits a pronounced cytopathic effect and a high viral titer, N is cleaved by caspases. In contrast, in SARS-CoV-infected Caco-2 cells, which show a moderate cytopathic effect and a low viral titer, this processing of N was not observed. To further verify these observations, we transiently expressed N in different cell lines. Caco-2 and N2a cells served as models for persistent SARS-CoV infection, whereas Vero E6 and A549 cells did as prototype cell lines lytically infected by SARS-CoV. The experiments revealed that N induces the intrinsic apoptotic pathway, resulting in processing of N at residues 400 and 403 by caspase-6 and/or caspase-3. Of note, caspase activation is highly cell type specific in SARS-CoV-infected as well as transiently transfected cells. In Caco-2 and N2a cells, almost no N-processing was detectable. In Vero E6 and A549 cells, a high proportion of N was cleaved by caspases. Moreover, we examined the subcellular localization of SARS-CoV N in these cell lines. In transfected Vero E6 and A549 cells, SARS-CoV N was localized both in the cytoplasm and nucleus, whereas in Caco-2 and N2a cells, nearly no nuclear localization was observed. In addition, our studies indicate that the nuclear localization of N is essential for its caspase-6-mediated cleavage. These data suggest a correlation among the replication cycle of SARS-CoV, subcellular localization of N, induction of apoptosis, and the subsequent activation of caspases leading to cleavage of N.
authors.affiliation: Institute of Virology, Technical University of Munich, Trogerstr. 30, 81675 Munich, Germany.
authors.forename: Claudia
authors.initials: C
authors.lastname: Diemer
authors.forename: Martha
authors.initials: M
authors.lastname: Schneider
authors.forename: Judith
authors.initials: J
authors.lastname: Seebach
authors.forename: Janine
authors.initials: J
authors.lastname: Quaas
authors.forename: Gert
authors.initials: G
authors.lastname: Frösner
authors.forename: Hermann M
authors.initials: HM
authors.lastname: Schätzl
authors.forename: Sabine
authors.initials: S
authors.lastname: Gilch
mesh_terms: D000818:Animals; D053148:Caspase 3 / Q000378:metabolism*; D053178:Caspase 6 / Q000378:metabolism*; D002460:Cell Line; D002467:Cell Nucleus / Q000737:chemistry; D002522:Chlorocebus aethiops; D018352:Coronavirus Infections / Q000378:metabolism*; D000086462:Coronavirus Nucleocapsid Proteins; D003593:Cytoplasm / Q000737:chemistry; D006801:Humans; D019590:Nucleocapsid Proteins / Q000378:metabolism*; D045473:Severe acute respiratory syndrome-related coronavirus / Q000378:metabolism*
chemical_list: D000086462:Coronavirus Nucleocapsid Proteins; D019590:Nucleocapsid Proteins; D053148:Caspase 3; D053178:Caspase 6