Unique Interferon Pathway Regulation by the ANDV Nucleocapsid Protein is Conferred by Phosphorylation of Serine 386
[Thesis]
Simons, Matthew James
Mackow, Erich R.
State University of New York at Stony Brook
2019
144
Ph.D.
State University of New York at Stony Brook
2019
Hantaviruses nonlytically infect the endothelial cell lining of capillaries to cause edematous or hemorrhagic diseases. Hantaviruses found in the Americas infect virtually all endothelial cells of the pulmonary vasculature and cause highly lethal acute pulmonary edema and respiratory distress termed hantavirus pulmonary syndrome (HPS). The Andes hantavirus (ANDV) is the only hantavirus reported to spread person to person and cause lethal HPS-like disease in immunocompetent Syrian hamsters. Our lab has shown that pathogenic hantaviruses regulate early innate immune responses to successfully replicate in endothelial cells. Our lab recently revealed that the ANDV nucleocapsid (N) protein uniquely inhibits RIG/MDA5 directed type I interferon (IFN) responses by preventing TBK1 activation and subsequent IRF3 phosphorylation. Thus far, no other pathogenic hantavirus nucleocapsid proteins have been shown to share this unique function. To define residues critical for ANDV N to regulate IFN responses, amino acid exchanges were performed between N proteins from ANDV and Maporal virus (MAPV), a S. American hantavirus that does not cause human disease, but which contains a nearly identical N protein. We found that MAPV N fails to inhibit IFN induction, and that replacing ANDV residues 252-296 with a hypervariable domain (HVD) from MAPV N prevented IFN regulation. In addition, singularly changing ANDV residue 386 from serine to histidine, present in MAPV N, or alanine in other hantaviruses, prevented ANDV N from inhibiting IFN induction. In contrast, an ANDV S386D mutant robustly inhibited IRF3 phosphorylation and IFN induction. Although single H386S or H386D substitutions within the MAPV N failed to inhibit IFN induction, adding both ANDV HVD and H386D to MAPV N blocked TBK1 directed IRF3 phosphorylation. IFN regulation by ANDV N after substituting phospho-serine mimetic aspartic acid for serine (S386D), suggested that S386 phosphorylation directs ANDV N to inhibit IFN induction. Phosphorylation of S386 was confirmed by LC/MS/MS analysis of ANDV N immunoprecipitated from ANDV infected cells. A potential role for the ANDV HVD in kinase recruitment is suggested by findings that the ANDV HVD is required for IFN regulation when S386 is present, but dispensable for IFN regulation when ANDV N contains phosphomimetic D386. These findings reveal IFN regulating virulence determinants within the ANDV N protein that may be used to attenuate ANDV and suggest cellular kinases as potential therapeutic targets for restricting ANDV replication and spread.