Molekulare, zellbiologische und bioinformatische Charakterisierung mitochondrialer PPR-Proteine aus Arabidopsis thaliana

In dieser Arbeit werden zwei mitochondriale PPR-Proteine (pentatricopeptide repeat-Proteine) aus Arabidopsis thaliana und ihre Rolle im mitochondrialen RNA-Metabolismus charakterisiert

The P-type pentatricopeptide repeat protein DWEORG1 is a non-previously reported rPPR protein of Arabidopsis mitochondria

Gene expression in plant mitochondria is mainly regulated by nuclear-encoded proteins on a post-transcriptional level. Pentatricopeptide repeat (PPR) proteins play a major role by participating in mRNA stability, splicing, RNA editing, and translation initiation. PPR proteins were also shown to be part of the mitochondrial ribosome (rPPR proteins), which may act as regulators of gene expression in plants. In this study, we focus on a mitochondrial-located P-type PPR protein-DWEORG1-from Arabidopsis thaliana. Its abundance in mitochondria is high, and it has a similar expression pattern as rPPR proteins. Mutant dweorg1 plants exhibit a slow-growth phenotype. Using ribosome profiling, a decrease in translation efficiency for cox2, rps4, rpl5, and ccmFN2 was observed in dweorg1 mutants, correlating with a reduced accumulation of the Cox2 protein in these plants. In addition, the mitochondrial rRNA levels are significantly reduced in dweorg1 compared with the wild type. DWEORG1 co-migrates with the ribosomal proteins Rps4 and Rpl16 in sucrose gradients, suggesting an association of DWEORG1 with the mitoribosome. Collectively, this data suggests that DWEORG1 encodes a novel rPPR protein that is needed for the translation of cox2, rps4, rpl5, and ccmFN2 and provides a stabilizing function for mitochondrial ribosomes

Prevention and Mitigation of Experimental Autoimmune Encephalomyelitis by Murine β-Defensins via Induction of Regulatory T Cells

The antimicrobial peptide murine β-defensin-14 (mBD14) was found to exert, in addition to its antimicrobial activity, the capacity to induce regulatory T cells as demonstrated in the model of contact hypersensitivity. Because it is induced by ultraviolet radiation, mBD14 may contribute to the antigen-specific immunosuppression by ultraviolet radiation. To prove whether this applies also for other immunologic models and because ultraviolet radiation appears to have beneficial effects on multiple sclerosis, we utilized the model of experimental autoimmune encephalomyelitis. Injection of mBD14 into mice before immunization with myelin oligodendrocyte glycoprotein caused amelioration of the disease with less central nervous system inflammation and decreased levels of proinflammatory cytokines and cytotoxic T cells. The beneficial effect was due to Foxp3+ regulatory T cells because it was lost on in vivo depletion of regulatory T cells. mBD14, however, also acts in a therapeutic setting, because injection of mBD14 into mice with clinical features of experimental autoimmune encephalomyelitis reduced the clinical score significantly. Human β-defensin-3, the human orthologue of mBD14, induced in vitro regulatory T cell-specific markers in CD4+CD25− T cells, shifting these nonregulatory cells into a regulatory phenotype with suppressive features. Thus, defensins may represent candidates worth being further pursued for the therapy of multiple sclerosis

The AHR represses nucleotide excision repair and apoptosis and contributes to UV-induced skin carcinogenesis.

Ultraviolet B (UVB) radiation induces mutagenic DNA photoproducts, in particular cyclobutane pyrimidine dimers (CPDs), in epidermal keratinocytes (KC). To prevent skin carcinogenesis, these DNA photoproducts must be removed by nucleotide excision repair (NER) or apoptosis. Here we report that the UVB-sensitive transcription factor aryl hydrocarbon receptor (AHR) attenuates the clearance of UVB-induced CPDs in human HaCaT KC and skin from SKH-1 hairless mice. Subsequent RNA interference and inhibitor studies in KC revealed that AHR specifically suppresses global genome but not transcription-coupled NER. In further experiments, we found that the accelerated repair of CPDs in AHR-compromised KC depended on a modulation of the p27 tumor suppressor protein. Accordingly, p27 protein levels were increased in AHR-silenced KC and skin biopsies from AHR-/- mice, and critical for the improvement of NER. Besides increasing NER activity, AHR inhibition was accompanied by an enhanced occurrence of DNA double-strand breaks triggering KC apoptosis at later time points after irradiation. The UVB-activated AHR thus acts as a negative regulator of both early defense systems against carcinogenesis, NER and apoptosis, implying that it exhibits tumorigenic functions in UVB-exposed skin. In fact, AHR-/- mice developed 50% less UVB-induced cutaneous squamous cell carcinomas in a chronic photocarcinogenesis study than their AHR+/+ littermates. Taken together, our data reveal that AHR influences DNA damage-dependent responses in UVB-irradiated KC and critically contributes to skin photocarcinogenesis in mice

Correction to: The AHR represses nucleotide excision repair and apoptosis and contributes to UV-induced skin carcinogenesis.

An amendment to this paper has been published and can be accessed via a link at the top of the paper

The AHR represses nucleotide excision repair and apoptosis and contributes to UV-induced skin carcinogenesis

Ultraviolet B (UVB) radiation induces mutagenic DNA photoproducts, in particular cyclobutane pyrimidine dimers (CPDs), in epidermal keratinocytes (KC). To prevent skin carcinogenesis, these DNA photoproducts must be removed by nucleotide excision repair (NER) or apoptosis. Here we report that the UVB-sensitive transcription factor aryl hydrocarbon receptor (AHR) attenuates the clearance of UVB-induced CPDs in human HaCaT KC and skin from SKH-1 hairless mice. Subsequent RNA interference and inhibitor studies in KC revealed that AHR specifically suppresses global genome but not transcription-coupled NER. In further experiments, we found that the accelerated repair of CPDs in AHR-compromised KC depended on a modulation of the p27 tumor suppressor protein. Accordingly, p27 protein levels were increased in AHR-silenced KC and skin biopsies from AHR-/- mice, and critical for the improvement of NER. Besides increasing NER activity, AHR inhibition was accompanied by an enhanced occurrence of DNA double-strand breaks triggering KC apoptosis at later time points after irradiation. The UVB-activated AHR thus acts as a negative regulator of both early defense systems against carcinogenesis, NER and apoptosis, implying that it exhibits tumorigenic functions in UVB-exposed skin. In fact, AHR-/- mice developed 50% less UVB-induced cutaneous squamous cell carcinomas in a chronic photocarcinogenesis study than their AHR+/+ littermates. Taken together, our data reveal that AHR influences DNA damage-dependent responses in UVB-irradiated KC and critically contributes to skin photocarcinogenesis in mice