The coronavirus endoribonuclease Nsp15 interacts with retinoblastoma tumor suppressor protein.
Coronaviruses encode an endoribonuclease, Nsp15, which has a poorly defined role in infection. Sequence analysis revealed a retinoblastoma protein-binding motif (LXCXE/D) in the majority of the Nsp15 of the severe acute respiratory syndrome coronavirus (SARS-CoV) and its orthologs in the alpha and beta coronaviruses. The endoribonuclease activity of the SARS-CoV Nsp15 (sNsp15) was stimulated by retinoblastoma protein (pRb) in vitro, and the two proteins can be coimmunoprecipitated from cellular extracts. Mutations in the pRb-binding motif rendered sNsp15 to be differentially modified by ubiquitin in cells, and cytotoxicity was observed upon its expression. Expression of the sNsp15 in cells resulted in an increased abundance of pRb in the cytoplasm, decreased overall levels of pRb, an increased proportion of cells in the S phase of the cell cycle, and an enhanced expression from a promoter normally repressed by pRb. The endoribonuclease activity of the mouse hepatitis virus (MHV) A59 Nsp15 was also increased by pRb in vitro, and an MHV with mutations in the LXCXE/D-motif, named vLC, exhibited a smaller plaque diameter and reduced the virus titer by ∼1 log. Overexpression of pRb delayed the viral protein production by wild-type MHV but not by vLC. This study reveals that pRb and its interaction with Nsp15 can affect coronavirus infection and adds coronaviruses to a small but growing family of RNA viruses that encode a protein to interact with pRb.
Department of Molecular and Cellular Biochemistry, Indiana University, Bloomington, Indiana, USA. kanchan@indiana.edu
Kanchan
K
Bhardwaj
Pinghua
P
Liu
Julian L
JL
Leibowitz
C Cheng
CC
Kao
D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D017209:Apoptosis / Q000235:genetics; D001665:Binding Sites; D002460:Cell Line; D018352:Coronavirus Infections / Q000378:metabolism; D006224:Cricetinae; D004722:Endoribonucleases / Q000235:genetics / Q000378:metabolism*; D005786:Gene Expression Regulation; D006801:Humans; D051379:Mice; D008958:Models, Molecular; D006517:Murine hepatitis virus / Q000201:enzymology* / Q000235:genetics; D009154:Mutation; D011485:Protein Binding; D054730:Protein Interaction Domains and Motifs; D021381:Protein Transport; D016160:Retinoblastoma Protein / Q000235:genetics / Q000378:metabolism*; D017361:Viral Nonstructural Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
D016160:Retinoblastoma Protein; D017361:Viral Nonstructural Proteins; D004722:Endoribonucleases