OAS antiviral response (Homo sapiens)
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Description
The human oligoadenylate synthetase (OAS) family consists of four proteins whose production is stimulated by interferon, OAS1, OAS2, OAS3, and OASL. The first three members have the 2'-5'-oligoadenylate synthetase activity for which the family is named (Sadler AJ & Williams BR 2008), whereas OASL is devoid of this activity despite sharing significant sequence similarity with the other OAS proteins (Zhu J et al. 2015). OAS1, 2, and 3 are activated by double-stranded RNA to synthesize 5'-triphosphorylated 2'-5'-oligoadenylates (2-5A) from ATP (Kerr IM & Brown RE 1978). The 2-5A serve as chemically unique second messengers that induce regulated RNA decay by activating ribonuclease L (RNase L), thus mediating antiviral innate immunity (Zhou A et al. 1993; Lin RJ et al. 2009; Huang H et al. 2014; Han Y et al. 2014). RNase L has also been implicated in antibacterial innate immunity (Li XL et al. 2008). RNase L cleaves single-stranded RNA (ssRNA) in U-rich sequences, typically after UU or UA dinucleotides leaving a 5'-OH and 2',3'-cyclic phosphate (Floyd-Smith G et al. 1981; Wreschner DH et al.1981; Cooper DA et al. 2014).
Some OAS proteins have additional or alternative antiviral functions that are independent of RNase L activity (Perelygin AA et al., 2002; Kristiansen H et al. 2011). The precise mechanisms of RNase L-independent OAS antiviral activities remain to be fully elucidated. View original pathway at Reactome.</div>
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2'-3' cyclic
phosphateAnnotated Interactions
RNase L possesses nine ankyrin repeats (the 9th being incomplete) in the N-terminus, and pseudokinase and nuclease domains in the C-terminus, which is also termed the kinase-extension nuclease (KEN) domain (Hassel BA et al. 1993; Tanaka N et al. 2004; Han Y et al. 2014; Huang H et al. 2014). The monomeric RNase L lacks nucleolytic activity, however, deletion of ankyrin repeats caused constitutive, albeit reduced, ribonuclease activity (Dong B et al. 1997). Crystal structure data indicate that 2-5A binds to the second and fourth ankyrin repeats and the pseudokinase domain (Tanaka N et al. 2004; Huang H et al. 2014; Han Y et al. 2014). These interactions, in conjunction with binding between the pseudokinase domains of the two protomers, mediate dimerization and enzymatic activation within minutes (Huang H et al. 2014; Han Y et al. 2012, 2014). Once active, RNase L cleaves ssRNA, including cellular mRNA and rRNA as well as microbial RNAs. In uninfected cells RNase L interacts with the actin-binding protein filamin A (FLNA) to modulate the actin cytoskeleton and inhibit virus entry into cells (Malathi K et al. 2014; Ezelle HJ et al. 2016). Upon infection and activation of its enzymatic activity by 2-5A, RNase L dissociates from FLNA to mediate its antiviral signaling (Malathi K et al. 2014; Ezelle HJ et al. 2016).
The Reactome event shows a cleavage of 2-5A by RVA protein VP3 as an example of viral 2',5'-PDE activity that antagonizes dsRNA signaling to RNase L.
2'-3' cyclic
phosphate2'-3' cyclic
phosphate