Functional analysis of the non-structural protein of the M (NSm) segment of orthobunyavirus Oropouche

Author(s)

Marjorie Cornejo Pontelli

• Document type: Doctoral Thesis
• Press: Ribeirão Preto.
• Institution: Universidade de São Paulo (USP). Faculdade de Medicina de Ribeirão Preto (PCARP/BC)
• Defense date: 2019-02-08

Examining board members

Eurico de Arruda Neto; Clarissa Rosa de Almeida Damaso; José Luiz Proença Modena; Mariana Kiomy Osako; Luis Lamberti Pinto da Silva

• Advisor: Eurico de Arruda Neto

Abstract

Oropouche virus is classified in Bunyavirales order, family Peribunyaviridae, genus Orthobunyavirus and it\'s one of the most frequent causes of arboviruses in Brazil. OROV is endemic in the Amazon region, where it infected half million cases in documented outbreaks. However, it\'s recently gaining more attention due to an occurrence in humans and primates outside this region. OROV is transmitted by the bite of Culicoides paraensis vector and causes a febrile disease. Its genome is composed of three negative RNA strands (L, M and S) that codes the structural and non-structural viral proteins: NSm and NSs. NSs is a known virulence factor in the Orthobunyavirus genus, but nearly nothing is known about NSm function. Evidence obtained with other orthobunyaviruses showed that NSm is involved with viral particle assembly and morphogenesis. But there are not information\'s about OROVs NSm function. With the development of this work it was possible to discover that NSm protein it is not essential for progeny production, but it is involved with the canonical assembly pathway in Golgi complex. The absence of NSm modifies organelles recruitment to viral factories, diminishing viral factories area, affecting progeny production in the exponential growth phase in the replication curve. Another important discovery is that NSm is a virulence attenuator factor since the OROV NSm mutant is highly pathogenic in a mouse model. The opposite was observed in OROV NSs mutant, being less lethal compared to OROV wild type. Moreover, OROV mutant lacking both non-structural proteins infect human peripheral blood cells from myelocytic lineage, in similar ways of OROV wild-type, but with altered TNF-a cytokine production, suggesting that these proteins are involved with OROV pathogenicity. Heterologous NSm expression demonstrated that its coding region by itself it is not functional, indicating that is necessary to express elements from the M polyprotein to the correct destination. Taking together, these observations show that OROVs NSm is involved with viral factories assembly and viral morphogenesis, and both NSm and NSs are related to pathogenicity in a mouse model. OROV mutant lacking both non-structural proteins its highly attenuated in vivo, and it can be an essential tool to develop a vaccine to this virus. These new data contribute to the discovery of possible therapeutic targets in treating this virus. (AU)

• FAPESP's process: 15/05354-0 - Functional analysis of the M segment non-structural protein (NSm) of Orthobunyavirus Oropouche
• Grantee: Marjorie Cornejo Pontelli
• Support Opportunities: Scholarships in Brazil - Doctorate