Biology subjects

Goradia, A.

Publications and source records attributed to Goradia, A..

3 recordsLinked to original sources

bioRxiv2023

Over-expression of ADAR1 in mice does not initiate or accelerate cancer formation in vivo.

Adenosine to inosine editing (A-to-I) in regions of double stranded RNA (dsRNA) is mediated by adenosine deaminase acting on RNA 1 (ADAR1) or ADAR2. ADAR1 and A-to-I editing levels are increased in many human cancers. It is not established if elevated ADAR1 represents a driver or passenger during cancer formation. We established a series of murine alleles to allow in vivo overexpression of ADAR1, its individual isoforms or mutant forms of ADAR1 to understand how it contributes to cancer pathogenesis. The widespread overexpression of ADAR1 or either the p110 or p150 isoforms as sole lesions was well tolerated and did not result in cancer formation. Therefore, ADAR1 overexpression alone is not sufficient to initiate cancer. We demonstrate that endogenous ADAR1 and A-to-I editing levels increased upon immortalization by loss of p53 in murine cells, consistent with the observations from human cancers. We tested if ADAR1 overexpression could co- operate with cancer initiated by loss of tumour suppressors using a model of osteosarcoma. We did not see a disease potentiating or modifying effect of overexpressing ADAR1 or its isoforms. We conclude that the increase in ADAR1 expression and A-to-I editing in cancers is a passenger, rather than a driver, of tumor formation.

cancer biology↗

bioRxiv2023

ADAR1p150 Prevents MDA5 and PKR Activation via Distinct Mechanisms to Avert Fatal Autoinflammation

Effective immunity requires the innate immune system to distinguish foreign (non-self) nucleic acids from cellular (self) nucleic acids. Cellular double-stranded RNAs (dsRNAs) are edited by the RNA editing enzyme ADAR1 to prevent their dsRNA structure pattern being recognized as viral dsRNA by cytoplasmic dsRNA sensors including MDA5, PKR and ZBP1. A loss of ADAR1-mediated RNA editing of cellular dsRNA activates MDA5. However, additional RNA editing-independent functions of ADAR1 have been proposed, but a specific mechanism has not been delineated. We now demonstrate that the loss of ADAR1-mediated RNA editing specifically activates MDA5, while loss of the cytoplasmic ADAR1p150 isoform or its dsRNA binding activity enabled PKR activation. Deleting both MDA5 and PKR resulted in complete rescue of the embryonic lethality of Adar1p150-/- mice to adulthood, contrasting with the limited or no rescue by removing MDA5, PKR or ZBP1 alone, demonstrating that this is a species conserved function of ADAR1p150. Our findings demonstrate that MDA5 and PKR are the primary in vivo effectors of fatal autoinflammation following the loss of ADAR1p150.

genetics↗

bioRxiv2022

The most common human ADAR1p150 Zα domain mutation P193A is well tolerated in mice.

ADAR1 mediated A-to-I RNA editing is a self/non-self discrimination mechanism for cellular double stranded RNAs. ADAR mutations are one cause of Aicardi-Goutieres Syndrome, an inherited paediatric encephalopathy, broadly classed as a "Type I interferonopathy". The most common ADAR1 mutation is a proline 193 alanine (p.P193A) mutation, mapping to the ADAR1p150 isoform specific Z domain. We report the development of an independent murine P195A knock-in mouse, homologous to the human P193A mutation. The Adar1P195A/P195A mice are largely normal and the mutation is well tolerated. Contrasting with previous reports when the P195A mutation was compounded with an ADAR1 null allele, the majority of mice have only a modest reduction in weaning weight and survived long-term. Severe runting and shortened survival of Adar1P195A/-animals are dependent on the parental genotype. The P195A mutation is well tolerated in vivo and the loss of MDA5 is sufficient to completely rescue the Adar1P195A/- mice.

genetics↗