Iwona Migdal

Up-frameshift protein 1 (UPF1) plays the role of a vital controller for transcripts, ready to react in the event of an incorrect translation mechanism. It is well known as one of the key elements involved in mRNA decay pathways and participates in transcript and protein quality control in several different aspects. Firstly, UPF1 specifically degrades premature termination codon (PTC)-containing products in a nonsense-mediated mRNA decay (NMD)-coupled manner. Additionally, UPF1 can potentially act as an E3 ligase and degrade target proteins independently from mRNA decay pathways. Thus, UPF1 protects cells against the accumulation of misfolded polypeptides. However, this multitasking protein may still hide many of its functions and abilities. In this article, we summarize important discoveries in the context of UPF1, its involvement in various cellular pathways, as well as its structural importance and mutational changes related to the emergence of various pathologies and disease states. Even though the state of knowledge about this protein has significantly increased over the years, there are still many intriguing aspects that remain unresolved.

Compared with yeast, our knowledge on members of the ATP-independent plant mitochondrial proteolytic machinery is rather poor. In the present study, using confocal microscopy and immunoblotting, we proved that homologs of yeast Oma1, Atp23, Imp1, Imp2, and Oct1 proteases are localized in Arabidopsis mitochondria. We characterized these components of the ATP-independent proteolytic system as well as the earlier identified protease, AtICP55, with an emphasis on their significance in plant growth and functionality in the OXPHOS system. A functional complementation assay demonstrated that out of all the analyzed proteases, only AtOMA1 and AtICP55 could substitute for a lack of their yeast counterparts. We did not observe any significant developmental or morphological changes in plants lacking the studied proteases, either under optimal growth conditions or after exposure to stress, with the only exception being retarded root growth in oma1-1, thus implying that the absence of a single mitochondrial ATP-independent protease is not critical for Arabidopsis growth and development. We did not find any evidence indicating a clear functional complementation of the missing protease by any other protease at the transcript or protein level. Studies on the impact of the analyzed proteases on mitochondrial bioenergetic function revealed that out of all the studied mutants, only oma1-1 showed differences in activities and amounts of OXPHOS proteins. Among all the OXPHOS disorders found in oma1-1, the complex V deficiency is distinctive because it is mainly associated with decreased catalytic activity and not correlated with complex abundance, which has been observed in the case of supercomplex I+III2 and complex I deficiencies. Altogether, our study indicates that despite the presence of highly conservative homologs, the mitochondrial ATP-independent proteolytic system is not functionally conserved in plants as compared with yeast. Our findings also highlight the importance of AtOMA1 in maintenance of proper function of the OXPHOS system as well as in growth and development of A. thaliana.

The proposed research outlines a serious common concern of Salmonella resistance to antimicrobials following prolonged exposure to the disinfectants (biocides). These phenotypes of bacteria could potentially result in hard to treat infections. Typical for avian sources, biocide sensitive S. enterica subsp. enterica serovars: Typhimurium, Enteritidis, Virchow and Zanzibar and their isogenic biocide-tolerant variants were studied in order to investigate bacteriostatic effect of two commercially available biocide formulations: potassium peroxymonosulfate (P) and dodecylamine based structure (triamine, D). We found that cultivating of the bacteria in the medium supplemented with a blend containing P did not influence their antibiotic susceptibility pattern. In contrast, tolerance of bacteria to D compound resulted in resistance to co-trimoxazole, cefotaxime and ciprofloxacin of which two cefotaxime and ciprofloxacin are used commonly for the treatment of invasive Salmonella infections in humans. The dependency between OMP patterns and the level of Salmonella survival in media containing the biocides was observed merely in serovar Typhimurium. In conclusion, these results suggest that Salmonella strains challenged by prolonged treatment with the disinfectants become resistant to antibiotics, however it depends on Salmonella serovar and the chemical used. This paper also highlights the loop-mediated isothermal amplification (LAMP) as a technique that offers great benefits to microbiological detecting of Salmonella species in the samples.

The existence of a proteolytic system which can specifically recognize and cleave proteins in mitochondria is now well established. The components of this system comprise processing peptidases, ATP‐dependent peptidases and oligopeptidases. A short overview of experimentally confirmed proteases mainly from Arabidopsis thaliana is provided. The role of the mitochondrial peptidases in plant growth and development is emphasized. We also discuss the possibility of existence of as yet unidentified plant homologs of yeast mitochondrial ATP‐independent proteases.

The Saccharomyces cerevisiae High-Osmolarity Glycerol (HOG) pathway is a conserved mitogen-activated protein kinase (MAPK) signal transduction system that often serves as a model to analyze systems level properties of MAPK signaling. Hog1, the MAPK of the HOG-pathway, can be activated by various environmental cues and it controls transcription, translation, transport, and cell cycle adaptations in response to stress conditions. A powerful means to study signaling in living cells is to use kinase inhibitors; however, no inhibitor targeting wild-type Hog1 exists to date. Herein, we describe the design, synthesis, and biological application of small molecule inhibitors that are cell-permeable, fast-acting, and highly efficient against wild-type Hog1. These compounds are potent inhibitors of Hog1 kinase activity both in vitro and in vivo. Next, we use these novel inhibitors to pinpoint the time of Hog1 action during recovery from G₁ checkpoint arrest, providing further evidence for a specific role of Hog1 in regulating cell cycle resumption during arsenite stress. Hence, we describe a novel tool for chemical genetic analysis of MAPK signaling and provide novel insights into Hog1 action.

The stress‐activated kinase Hog1p mediates arsenic tolerance by decreasing arsenite influx through the aquaglyceroporin Fps1p in Saccharomyces cerevisiae. Unexpectedly, we found that overexpression of FPS1 increased arsenite tolerance suggesting a physiological role of Fps1p in arsenic detoxification. Consistently, during arsenite treatment transcription of FPS1 gene was strongly upregulated, while Fps1p was not degraded and remained localized to the plasma membrane. Moreover, deletion of FPS1 gene resulted in arsenate sensitivity. Finally, transport experiments revealed that Fps1p in concert with the arsenite transporter Acr3p mediates arsenite efflux.

Cells slow down cell cycle progression in order to adapt to unfavorable stress conditions. Yeast (Saccharomyces cerevisiae) responds to osmotic stress by triggering G(1) and G(2) checkpoint delays that are dependent on the mitogen-activated protein kinase (MAPK) Hog1. The high-osmolarity glycerol ( HOG) pathway is also activated by arsenite, and the hog1 Delta mutant is highly sensitive to arsenite, partly due to increased arsenite influx into hog1 Delta cells. Yeast cell cycle regulation in response to arsenite and the role of Hog1 in this process have not yet been analyzed. Here, we found that long-term exposure to arsenite led to transient G(1) and G(2) delays in wild-type cells, whereas cells that lack the HOG1 gene or are defective in Hog1 kinase activity displayed persistent G(1) cell cycle arrest. Elevated levels of intracellular arsenite and "cross talk" between the HOG and pheromone response pathways, observed in arsenite-treated hog1 Delta cells, prolonged the G(1) delay but did not cause a persistent G(1) arrest. In contrast, deletion of the SIC1 gene encoding a cyclin-dependent kinase inhibitor fully suppressed the observed block of G(1) exit in hog1 Delta cells. Moreover, the Sic1 protein was stabilized in arsenite-treated hog1 Delta cells. Interestingly, Sic1-dependent persistent G(1) arrest was also observed in hog1 Delta cells during hyperosmotic stress. Taken together, our data point to an important role of the Hog1 kinase in adaptation to stress-induced G(1) cell cycle arrest.