The Cellular Localization of the p42 and p46 Oligoadenylate Synthetase 1 Isoforms and Their Impact on Mitochondrial Respiration

Abstract

The importance of the IFN-induced oligoadenylate synthetase (OAS) proteins and the OAS/RNase L pathway in the innate response against viral pathogens is well-established, however the observed differences in anti-viral activity between the human OAS1 p46 and p42 isoforms are not fully understood. The protein expression of these isoforms is determined by the SNP rs10774671, either being an A or a G allele resulting in expression of either the p42 or the p46 isoform. Using fluorescence microscopy and immunoblot analysis of fractionated cell samples, we show here that the CaaX motif is of key importance to the cellular localization. The OAS1 p42 isoform is mainly located in the cytosol, whereas the p46 isoform with a C-terminal CaaX motif is translocated to membranous organelles, like the mitochondria. We furthermore observed differences between p42 and p46 in their effect on mitochondrial physiology using high resolution respirometry and fluorometry. Overexpression of OAS1 p42 and IFN-β treatment of HeLa cells (AA genotype) resulted in significantly increased respiration, which was not seen with p46 overexpression. The difference in subcellular localization and mitochondrial effect of these two OAS1 isoforms might help to explain the anti-viral mechanisms that differentiate these proteins.

All About the RNA: Interferon-Stimulated Genes That Interfere With Viral RNA Processes

“…A yeast two-hybrid screen for p42 and p44, predicted to be expressed by all humans ( 70 ), revealed different binding partners, suggesting that OAS1 unique C-terminal regions may alter protein-protein interactions mediating isoform-specific functions ( 69 ). In support of this hypothesis, p46 possesses a CaaX prenylation motif that causes it to localize to mitochondria, whereas p42 lacks the CaaX motif and is cytoplasmic ( 71 , 72 ). This difference in cellular localization is thought to contribute to their divergent impact on cellular respiration upon overexpression ( 72 ), and could contribute to their differential antiviral activity.…”

“…In support of this hypothesis, p46 possesses a CaaX prenylation motif that causes it to localize to mitochondria, whereas p42 lacks the CaaX motif and is cytoplasmic ( 71 , 72 ). This difference in cellular localization is thought to contribute to their divergent impact on cellular respiration upon overexpression ( 72 ), and could contribute to their differential antiviral activity.…”

Suppressing PAR ylation by 2′,5′‐oligoadenylate synthetase 1 inhibits DNA damage‐induced cell death

“…In the prostate cancer cell line PC3, OAS1 is predominantly nuclear, while both OAS2 and OAS3 are predominantly cytoplasmic. Recently, Martinsen group showed that subcellular localization of different subtypes of OAS1 was also genotype-specific: The p46 OAS1 isoform was found in mitochondria (Kjaer et al, 2014;Skrivergaard et al, 2019), while the p42 OAS1 isoform was found in the nucleus and cytoplasm (Skrivergaard et al, 2019); importantly, expression of the p42 and p46 OAS1 isoforms resulted in opposite effects on cellular respiration (Skrivergaard et al, 2019). Our SNP analysis showed that the cell lines used here, PC3 and HME, express the p42 subtype of OAS1 (Appendix Table S1).…”

“…The drug-and cancer-subtype specificity of these correlations underscores the role of particular mechanisms of drug action (i.e., the specific way each drug induces PARP1 as well as its action on other targets in the cancer cell), as well as of specific mutation/genetic landscapes of cancer subtypes, in the cancer cell response to therapy. Moreover, more detailed analysis, which takes in account particular OAS1 isoform expressed (p42 or p46), may be necessary, because of the opposite effect of these isoforms on cellular respiration, which may contribute to the Warburg effect in tumors (Skrivergaard et al, 2019).…”

A Prenylated dsRNA Sensor Protects Against Severe COVID-19 and is Absent in Horseshoe Bats

“…Remarkably, the C-terminus of p46 encodes a canonical CAAX-box prenylation signal (CTIL) that is absent from the p42 variant (Figure 4C), and predicted to be geranylgeranylated (Maurer-Stroh and Eisenhaber, 2005). Indeed, prenylation of OAS1 was proposed to alter the subcellular localization of OAS1, perhaps influencing mitochondrial respiration (Skrivergaard et al, 2019). We hypothesized that prenylated OAS1 is targeted to membranous viral replicative organelles and facilitates the sensing of CoV dsRNA (and perhaps many divergent RNA viruses that replicate within replicative organelles).…”