AID/APOBEC proteins are cytidine deaminases, which act within the innate immune response to protect the genome against the harmful effects of retroelements. The protective activity of mammalian APOBEC proteins is evident from clusters of hypermutations present in retroelements of mammalian genomes, but their role in host defense and their impact on genome evolution in other vertebrates is not known. In this study, we report the first evidence of cytidine deaminase activity in non-mammalian vertebrates, in the green anole lizard genome, where the oldest known APOBEC1 (A1) protein was recently discovered. Our results confirm that the lizard A1 protein is a potent cytidine deaminase and an inhibitor of retrotransposition. Our comparative analysis of the anti-retroelement activity of lizard and human APOBEC proteins showed that the mechanism of A1-induced LINE inhibition is evolutionary conserved and significantly different from that of human A3 proteins. Together with the editing detected in vertebrate LINE elements, our study indicates that AID/APOBEC anti-retroelement activity originates in early vertebrates. Our findings open new perspectives in AID/APOBEC protein research and are an important contribution to our understanding of their physiological roles and their impact on the evolution of vertebrate genomes.
COBISS.SI-ID: 27367975
We were able to show for the first time that human group X secreted phospholipase A2 (hGX sPLA2) induces lipid droplet (LD) formation in the highly tumorigenic MDA-MB-231 breast cancer cells in an enzyme activity-dependent manner, thereby stimulating cell proliferation and significantly prolonging cell survival under serum deprivation-induced stress. Our results suggested that free fatty acids, in particular oleic acid, released from membrane phospholipids by the action of hGX sPLA2, are substantially responsible for LD biogenesis and cell survival. It was also demonstrated that the mechanism of hGX-induced cell survival and lipid accumulation is associated with alterations in the expression of key lipogenic and β-oxidation enzymes, and modulation of AMP-activated protein kinase (AMPK) and protein B/Akt kinase signalling pathways. The pro-tumorigenic effects induced by hGX sPLA2 were abolished by etomoxir, suggesting a critical role for β-oxidation in hGX-induced LD formation and cell survival in breast cancer cells. The ability of hGX sPLA2 to act as a modulator of basic lipid metabolism and cancer cell survival is thus well established. This could have important implications in elucidating the role of hGX and other sPLA2s, such as hGV and hGIII, in cancer and human pathophysiology in general.
COBISS.SI-ID: 27087655
We have determined various steps in the pore-forming mechanism of equinatoxin II. We showed that binding of protein to the membrane is extremely rapid, that it is followed by the N-terminal helix insertion in the membrane and oligomerisation into the functional pore.
COBISS.SI-ID: 2836815
Membrane rafts are transient and unstable membrane microdomains that are enriched in sphingolipids, cholesterol, and specific proteins. Increasing experimental evidence on the crucial biological roles of membrane rafts under normal and pathological conditions require new techniques for their structural and functional characterization. In particular, fluorescence-labeled cytolytic proteins that interact specifically with molecules enriched in rafts are of increasing interest. Cholera toxin subunit B interacts specifically with raft-residing ganglioside GM1, and it has long been the lipid probe of choice for membrane rafts. Recently, four new pore-forming toxins have been proposed as selective raft markers: (i) equinatoxin II and (ii) lysenin, which specifically recognize sphingomyelin-enriched membrane domains; (iii) perfringolysin O, which selectively binds to membrane domains enriched in cholesterol; and (iv) ostreolysin, which requires a specific combination of two of the most important raft-residing lipids: sphingomyelin and cholesterol. Here, we review these four new derivatives of pore-forming toxins as new putative markers of these membrane microdomains.
COBISS.SI-ID: 2710351
We traced the genesis and regulatory wiring of the Metaviridae-derived domesticated genes (DGs) through phylogenomic analysis, using whole-genome information from more than 90 chordate genomes. Mammalian retroelement-derived DGs (RDDGs) have been shown to originate in several steps by independent domestication events and to diversify later by gene duplications. Analysis of syntenic loci has shown that diverse RDDGs and their chromosomal positions were fully established in the ancestor of placental mammals. By analysis of active Metaviridae lineages in amniotes, we have demonstrated that RDDGs originated from retroelement remains. During the domestication process, de novo acquisition of regulatory regions is shown to be a prerequisite for the survival of the DGs. The origin and evolution of de novo acquired promoters and untranslated regions in diverse mammalian RDDGs have been explained by comparative analysis of orthologous gene loci. The origin of placental mammal-specific innovations and adaptations, such as placenta and newly evolved brain functions, was most probably connected to the regulatory wiring of DGs and their rapid fixation in the ancestor of placental mammals.
COBISS.SI-ID: 26492711