Functional dissection of the C-terminal part of the transcriptional coactivator peroxisome proliferator-activated receptor gamma coactivator alpha (PGC-1[alpha])

The superfamily of nuclear receptors is a class of transcriptional regulators that includes the receptors for steroid hormones, thyroid hormones, retinoids and vitamin D. The superfamily also includes so-called orphan receptors, for which an activating ligand is unknown or not required. They regulate diverse biological processes, such as homeostasis, reproduction, development, and metabolism. To exert their functions in the activation of transcription, they need to recruit so-called coactivator protein complexes, many of which remodel the chromatin structure in promoter regions and help to recruit the basal RNA polymerase II transcription machinery. We and others identified the transcriptional coactivator PGC-1α. Its expression is induced by physiological signals such as cold, fasting, and exercise, and it turned out to be a central regulator of cellular energy homeostasis. The N-terminal part of PGC-1α harbors a strong transcriptional activation function and a nuclear receptor interaction domain. The Cterminal half of PGC-1α harbors several interesting motifs, including two serine/argininerich sequences, a putative RNA-binding domain, and an amino acid stretch containing a high percentage of glutamate residues. In this work, we describe the identification of proteins interacting with the C-terminal part of PGC-1α and the functional interaction of two of the identified proteins with PGC-1α. We show that the acetyltransferase Tip60 has both positive and negative effects on PGC1α-dependent transcription. In collaboration, we also show that the methyltransferase PRMT1 methylates PGC-1α and thereby enhances the activity of PGC-1α as a transcriptional coactivator

A Genetic Analysis of . . .

To find novel components in the glucocorticoid signal transduction pathway, we performed a yeast genetic screen to identify ligand-effect modulators (LEMs), proteins that modulate the cellular response to hormone. We isolated several mutants that conferred increased glucocorticoid receptor (GR) activity in response to dexamethasone and analyzed two of them in detail. These studies identify two genes, LEM3 and LEM4, which correspond to YNL323w and ERG6, respectively. LEM3 is a putative transmembrane protein of unknown function, and ERG6 is a methyltransferase in the ergosterol biosynthetic pathway. Analysi

Activation of nuclear receptor coactivator PGC-1α by arginine methylation

Peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α), a tissue-specific and inducible transcriptional coactivator for several nuclear receptors, plays a key role in energy metabolism. We report here that PGC-1α coactivator activity is potentiated by arginine methylation by protein arginine methyltransferase 1 (PRMT1), another nuclear receptor coactivator. Mutation of three substrate arginines in the C-terminal region of PGC-1α abolished the cooperative coactivator function of PGC-1α and PRMT1, and compromised the ability of PGC-1α to induce endogenous target genes. Finally, endogenous PRMT1 contributes to PGC-1α coactivator activity, and to the induction of genes important for mitochondrial biogenesis

Oxidative tryptophan modification by terpene- and squalene-hydroperoxides and a possible link to cross-reactions in diagnostic tests

Hydroperoxides can act as specific haptens and oxidatively modify proteins. Terpene hydroperoxides trigger unusually high frequencies of positive skin reactions in human patients if tested at high concentrations. It is unknown whether this is due to specific hapten formation. Here, we show that both terpene hydroperoxides and the endogenous hydroperoxide formed from squalene can oxidatively modify tryptophan. Oxidative modifications of Trp were recently postulated to explain cross-sensitization between unrelated photosensitizers. Current observations may extend this hypothesis: Oxidative events triggered by endogenous hydroperoxides and hydroperoxides/oxidants derived from xenobiotics might lead to a sensitized state detected by patch tests with high concentrations of hydroperoxides

Evaluating the performance of integrated approaches for hazard identification of skin sensitizing chemicals

The currently available animal-free methods for the detection of skin sensitizing potential of chemicals seem promising. However, no single method is able to comprehensively represent the complexity of the processes involved in skin sensitization. To ensure a mechanistic basis and cover the complexity, multiple methods should be integrated into a testing strategy, in accordance with the adverse outcome pathway that describes all key events in skin sensitization. Although current majority voting testing strategies have proven effective, the performance of individual methods is not taken into account. To that end, we designed a tiered strategy based on complementary characteristics of the included methods, and compared it to a majority voting approach. This tiered testing strategy was able to correctly identify all 41 chemicals tested. In terms of total number of experiments required, the tiered testing strategy requires less experiments compared to the majority voting approach. On the other hand, this tiered strategy is more complex due the number of different alternative methods required, and predicted costs are similar for both strategies. Both the tiered and majority voting strategies provide a mechanistic basis for skin sensitization testing, but the strategy most suitable for regulatory decision-making remains to be determined

Oxidative Tryptophan Modification by Terpene- and Squalene-Hydroperoxides and a Possible Link to Cross-Reactions in Diagnostic Tests

Hydroperoxides can act as specific haptens and oxidatively modify proteins. Terpene hydroperoxides trigger unusually high frequencies of positive skin reactions in human patients if tested at high concentrations. It is unknown whether this is due to specific hapten formation. Here, we show that both terpene hydroperoxides and the endogenous hydroperoxide formed from squalene can oxidatively modify tryptophan. Oxidative modifications of Trp were recently postulated to explain cross-sensitization between unrelated photosensitizers. Current observations may extend this hypothesis: Oxidative events triggered by endogenous hydroperoxides and hydroperoxides/oxidants derived from xenobiotics might lead to a sensitized state detected by patch tests with high concentrations of hydroperoxides