Szymanski, J. | Search bioRxiv

bioRxiv2023

RNA 5' terminal nucleotide determines the strength of the RIG-I/IFN signaling pathway

The interferon (IFN) response is crucial for antiviral activity, but its overstimulation can lead to a wide range of autoimmune disorders. The cytoplasmic pattern recognition receptor RIG-I detects viral double-stranded RNAs (dsRNAs) and endogenous polymerase III transcripts carrying a 5'-triphosphate (5'-ppp) or 5'-diphosphate (5'-pp) moiety, triggering phosphorylation of IRF3 and IFN immune response. While many viral RNAs initiate with 5'-ppp-adenosine (5'-pppA) and most endogenous Pol III transcripts in higher eukaryotes start with 5'-ppp-guanosine (5'-pppG), no apparent reason for this bias has been identified so far. Here we demonstrate that dsRNAs initiating with 5'-pppA trigger stronger RIG-I/IFN response than those starting with 5'-pppG. We show that several GTP-binding proteins interact preferentially with 5'-pppG RNAs. Finally, supplementation with guanosine, but not adenosine, which rapidly increases intracellular concentrations of GTP and ATP, respectively, eliminates the difference in immunogenicity between 5'-pppG and 5'-pppA RNAs. Our findings suggest that 5'-pppG RNAs may enable certain RNA viruses and Pol III transcripts to limit detection by innate immune receptors. These results offer new insights into the sequence-dependent activation of the RIG-I/IFN pathway and have important implications for both antiviral immunity and the role of Pol III-derived RNAs in autoimmune diseases.

molecular biology↗

bioRxiv2023

Molecular mechanisms of heavy metal adaptation of an extremophilic red alga Cyanidioschyzon merolae

The order of Cyanidiales comprise seven acido-thermophilic red microalgal species thriving in hot springs of volcanic origin characterized by extremely low pH, moderately high temperatures and the presence of elevated concentrations of sulphites and heavy metals that are prohibitive for most other organisms. Little is known about the molecular mechanisms of Cyanidiales long-term adaptation to such hostile environments, in particular to heavy metals, yet elucidation of these processes is important for understanding the evolution of the metabolic pathways underlying heavy metal detoxification for developing rational strategies for heavy metal bioremediation. Here, we investigated the long-term adaptive responses of Cyanidioschyzon merolae cells, a member of Cyanidiales, to extremely high nickel concentrations. Through complementary approaches based on physiological, microscopic and elemental analyses we dissect several molecular mechanisms underlying the long-term adaptation of this model extremophilic microalga to high Ni exposure. These include: (i) extrusion of Ni from the cells and lack of significant Ni accumulation inside the cells; (ii) maintenance of efficient photoprotective responses including non-photochemical quenching and state transitions; (iii) dynamic remodeling of the chloroplast ultrastructure such as formation of metabolically active prolamellar bodies and plastoglobuli together with loosening of the thylakoid membranes; (iv) activation of ROS amelioration metabolic pathways; and (v) preservation of the efficient respiratory chain functionality. All the dynamically regulated processes identified in this study underlie the remarkable adaptability of C. merolae to extremely high Ni levels that exceed by several orders of magnitude the levels of this heavy metal found in the natural environment of this extremophile.

cell biology↗