Repression of class I transcription by cadmium is mediated by the protein phosphatase 2A

Molecular Biology of Cadmium Toxicity in Saccharomyces cerevisiae

Cadmium (Cd) is a toxic heavy metal mainly originating from industrial activities and causes environmental pollution. To better understand its toxicity and pollution remediation, we must understand the effects of Cd on living beings. Saccharomyces cerevisiae (budding yeast) is an eukaryotic unicellular model organism. It has provided much scientific knowledge about cellular and molecular biology in addition to its economic benefits. Effects associated with copper and zinc, sulfur and selenium metabolism, calcium (Ca²⁺) balance/signaling, and structure of phospholipids as a result of exposure to cadmium have been evaluated. In yeast as a result of cadmium stress, "mitogen-activated protein kinase," "high osmolarity glycerol," and "cell wall integrity" pathways have been reported to activate different signaling pathways. In addition, abnormalities and changes in protein structure, ribosomes, cell cycle disruption, and reactive oxygen species (ROS) following cadmium cytotoxicity have also been detailed. Moreover, the key OLE1 gene that encodes for delta-9 FA desaturase in relation to cadmium toxicity has been discussed in more detail. Keeping all these studies in mind, an attempt has been made to evaluate published cellular and molecular toxicity data related to Cd stress, and specifically published on S. cerevisiae.

Quantitative proteomic analysis of trachea in fatting pig exposed to ammonia

Ammonia (NH₃) is considered as the main pollutant in livestock houses and air environment, and its adverse effects on animal and human health have attracted widespread attention. However, trachea proteomics respond to NH₃ is lacking, which is crucial to understanding how NH₃ induces respiratory damage. In this study, we performed labeled quantitative proteomic (TMT-MS) analysis in the trachea of fatting pigs exposed to NH₃ for 30 days. The proteomic results were then validated by Immunohistochemistry (IHC) and Parallel Reaction Monitoring (PRM). The results showed that a total of 126 differentially abundant proteins (DAPs) were identified (fold change <0.83 or > 1.2 and P < 0.05), including 70 differentially up-regulated proteins (DUPs) and 56 differentially down-regulated proteins (DDPs). These proteins were mainly located in intracellular regions and involved in immune response, metabolism and protein synthesis. The results of DAPs (EHHADH, RPL28, SLC25A6, TUBB6, CD14, CTSS, RPS11, RPL19, SLC25A5, RPS8, FABP3, RPL21, RPL34, RPL32, PDIA3, FBP1, HSPH1, SAR1A and SEC24C) verified by IHC and PRM were consistent with the proteomic results. The results of this study provided a basis and a novel insight for understanding the mechanism of NH₃-induced tracheal injury. SIGNIFICANCE: Ammonia (NH₃) is considered as the main pollutant in livestock houses and air environment, and its adverse effects on animal and human health have attracted widespread attention. However, trachea proteomics respond to NH₃ is lacking, which is crucial to understanding how NH₃ induces respiratory damage. Therefore, in this study, labeled quantitative proteomics (TMT-MS) was used to detect trachea tissue samples from finishing pigs in NH₃ exposure group and control group, and PRM method was used to further verify the highly abundant proteins in NH₃ exposure samples, so as to identify new diagnostic markers for NH₃ poisoning. The results of this study provided a basis and a novel insight for understanding the molecular pathological mechanism of NH₃-induced tracheal injury.

Genome-Scale Screening and Combinatorial Optimization of Gene Overexpression Targets to Improve Cadmium Tolerance in Saccharomyces cerevisiae

Heavy metal contamination is an environmental issue on a global scale. Particularly, cadmium poses substantial threats to crop and human health. Saccharomyces cerevisiae is one of the model organisms to study cadmium toxicity and was recently engineered as a cadmium hyperaccumulator. Therefore, it is desirable to overcome the cadmium sensitivity of S. cerevisiae via genetic engineering for bioremediation applications. Here we performed genome-scale overexpression screening for gene targets conferring cadmium resistance in CEN.PK2-1c, an industrial S. cerevisiae strain. Seven targets were identified, including CAD1 and CUP1 that are known to improve cadmium tolerance, as well as CRS5, NRG1, PPH21, BMH1, and QCR6 that are less studied. In the wild-type strain, cadmium exposure activated gene transcription of CAD1, CRS5, CUP1, and NRG1 and repressed PPH21, as revealed by real-time quantitative PCR analyses. Furthermore, yeast strains that contained two overexpression mutations out of the seven gene targets were constructed. Synergistic improvement in cadmium tolerance was observed with episomal co-expression of CRS5 and CUP1. In the presence of 200 μM cadmium, the most resistant strain overexpressing both CAD1 and NRG1 exhibited a 3.6-fold improvement in biomass accumulation relative to wild type. This work provided a new approach to discover and optimize genetic engineering targets for increasing cadmium resistance in yeast.

Promoter activity of earthworm metallothionein in mouse embryonic fibroblasts

The regulation of metallothionein (MT) gene expression as important part of the detoxification machinery is only scarcely known in invertebrates. In vertebrates, MT gene activation is mediated by the metal-transcription factor 1 (MTF-1) binding to metal response elements (MREs). In invertebrates, the mechanisms of MT gene activation seems to be more diverse. In some invertebrate species, MTF-1 orthologues as well as their ability to activate MT genes via MREs have been uncovered. Although earthworm MTs have been well studied, a MTF-1 orthologue has not yet been described and MT gene activation mechanisms are largely unknown. Analyses of the earthworm wMT2 promoter by reporter gene assays have been performed. We could show that the wMT2 promoter was active in mouse embryonic fibroblasts (NIH/3T3) as well as in mouse MTF-1-/-cells (DKO7). The presence of mouse MTF-1 (mMTF1) led to a significant increase in reporter gene activity. We observed that cadmium as well as zinc had an effect on promoter activity. In the presence of zinc, promoter activity doubled in NIH cells, however, we did not observe a significant effect in the DKO7 cell line. Cadmium decreased promoter activity in DKO7 cells, but this effect could be reversed by providing mMTF1 in a co-transfection experiment. We suggest that MT gene expression in the earthworm is not entirely dependent on a MRE binding protein. Interestingly, the shortest promoter fragment including MRE1 showed the highest promoter activity under control conditions.

Ser/Thr protein phosphatases in fungi: structure, regulation and function

Reversible phospho-dephosphorylation of proteins is a major mechanism for the control of cellular functions. By large, Ser and Thr are the most frequently residues phosphorylated in eukar-yotes. Removal of phosphate from these amino acids is catalyzed by a large family of well-conserved enzymes, collectively called Ser/Thr protein phosphatases. The activity of these enzymes has an enormous impact on cellular functioning. In this work we pre-sent the members of this family in S. cerevisiae and other fungal species, and review the most recent findings concerning their regu-lation and the roles they play in the most diverse aspects of cell biology.

Effect of cadmium on uptake of iron, zinc and copper and mRNA expression of metallothioneins in HepG2 cells in vitro

The intake of cadmium contaminated fish was mimicked by incubating human hepatoblastoma cells (Cell line HepG2) with a combination of different levels of cadmium (0-5μM) plus the n-3 fatty acids docosahexaenoic acid and eicosapentaenoic acid, which are typical for fish. Uptake of cadmium, iron, copper and zinc was measured by ICP-MS. In addition mRNA expression of two metallothioneins (mt1 g and mt1 m) was evaluated by real-time PCR. The obtained data shows that the presence of cadmium increases the uptake of iron and zinc into the HepG2 cells while the uptake of copper remains unaffected. The presence of the chosen fatty acids did not affect the uptake of either cadmium or iron, zinc and copper. The presence of already 1μM cadmium increased the mRNA expression of mt1 g and mt1 m significantly, while the fatty acids did not interfere with the effect of cadmium.

Splicing-Mediated Autoregulation Modulates Rpl22p Expression in Saccharomyces cerevisiae

In Saccharomyces cerevisiae, splicing is critical for expression of ribosomal protein genes (RPGs), which are among the most highly expressed genes and are tightly regulated according to growth and environmental conditions. However, knowledge of the precise mechanisms by which RPG pre-mRNA splicing is regulated on a gene-by-gene basis is lacking. Here we show that Rpl22p has an extraribosomal role in the inhibition of splicing of the RPL22B pre-mRNA transcript. A stem loop secondary structure within the intron is necessary for pre-mRNA binding by Rpl22p in vivo and splicing inhibition in vivo and in vitro and can rescue splicing inhibition in vitro when added in trans to splicing reactions. Splicing inhibition by Rpl22p may be partly attributed to the reduction of co-transcriptional U1 snRNP recruitment to the pre-mRNA at the RPL22B locus. We further demonstrate that the inhibition of RPL22B pre-mRNA splicing contributes to the down-regulation of mature transcript during specific stress conditions, and provide evidence hinting at a regulatory role for this mechanism in conditions of suppressed ribosome biogenesis. These results demonstrate an autoregulatory mechanism that fine-tunes the expression of the Rpl22 protein and by extension Rpl22p paralog composition according to the cellular demands for ribosome biogenesis.

Ribosomes are responsible for protein production in all living cells, serving as the grounds for the translation of genetic information from RNA to protein. Given the vital role of the ribosome in protein assembly, ribosome components are highly expressed and are subject to tight regulation. Some ribosomal proteins are also known to engage in extra-ribosomal activities. In our study, we demonstrate that the ribosomal protein Rpl22p is able to regulate its own expression by inhibiting the processing of its own RNA transcript, leading to degradation of the RNA. We also show that this self-imposed regulation plays a role in limiting RPL22 transcript levels in specific stress conditions. We suggest that this mechanism may impact the composition of ribosomes by influencing the availability of the Rpl22p paralogs.

Actions of Estrogenic Endocrine Disrupting Chemicals on Human Prostate Stem/Progenitor Cells and Prostate Carcinogenesis

Substantial evidences from epidemiological and animal-based studies indicate that early exposure to endocrine disrupting chemicals (EDCs) during the developmental stage results in a variety of disorders including cancer. Previous studies have demonstrated that early estrogen exposure results in life-long reprogramming of the prostate gland that leads to an increased incidence of prostatic lesions with aging. We have recently documented that bisphenol A (BPA), one of the most studied EDCs with estrogenic activity has similar effects in increasing prostate carcinogenic potential, supporting the connection between EDCs exposure and prostate cancer risk. It is well accepted that stem cells play a crucial role in development and cancer. Accumulating evidence suggest that stem cells are regulated by extrinsic factors and may be the potential target of hormonal carcinogenesis. Estrogenic EDCs which interfere with normal hormonal signaling may perturb prostate stem cell fate by directly reprogramming stem cells or breaking down the stem cell niche. Transformation of stem cells into cancer stem cells may underlie cancer initiation accounting for cancer recurrence, which becomes a critical therapeutic target of cancer management. We therefore propose that estrogenic EDCs may influence the development and progression of prostate cancer through reprogramming and transforming the prostate stem and early stage progenitor cells. In this review, we summarize our current studies and have updated recent advances highlighting estrogenic EDCs on prostate carcinogenesis by possible targeting prostate stem/progenitor cells. Using novel stem cell assays we have demonstrated that human prostate stem/progenitor cells express estrogen receptors (ER) and are directly modulated by estrogenic EDCs. Moreover, employing anin vivohumanized chimeric prostate model, we further demonstrated that estrogenic EDCs initiate and promote prostatic carcinogenesis in an androgen-supported environment. These findings support our hypothesis that prostate stem/progenitor cells may be the direct targets of estrogenic EDCs as a consequence of developmental exposure which carry permanent reprogrammed epigenetic and oncogenic events and subsequently deposit into cancer initiation and progression in adulthood.