Transcriptional and phenotypical alterations associated with a gradual benzo[a]pyrene-induced transition of human bronchial epithelial cells into mesenchymal-like cells.

The role of benzo[a]pyrene (BaP), a prominent genotoxic carcinogen and aryl hydrocarbon receptor (AhR) ligand, in tumor progression remains poorly characterized. We investigated the impact of BaP on the process of epithelial-mesenchymal transition (EMT) in normal human bronchial epithelial HBEC-12KT cells. Early morphological changes after 2-week exposure were accompanied with induction of SERPINB2, IL1, CDKN1A/p21 (linked with cell cycle delay) and chemokine CXCL5. After 8-week exposure, induction of cell migration and EMT-related pattern of markers/regulators led to induction of further pro-inflammatory cytokines or non-canonical Wnt pathway ligand WNT5A. This trend of up-regulation of pro-inflammatory genes and non-canonical Wnt pathway constituents was observed also in the BaP-transformed HBEC-12KT-B1 cells. In general, transcriptional effects of BaP differed from those of TGFß1, a prototypical EMT inducer, or a model non-genotoxic AhR ligand, TCDD. Carcinogenic polycyclic aromatic hydrocarbons could thus induce a unique set of molecular changes linked with EMT and cancer progression.

Polychlorinated environmental toxicants affect sphingolipid metabolism during neurogenesis in vitro.

Sphingolipids (SLs) are important signaling molecules and functional components of cellular membranes. Although SLs are known as crucial regulators of neural cell physiology and differentiation, modulations of SLs by environmental neurotoxicants in neural cells and their neuronal progeny have not yet been explored. In this study, we used in vitro models of differentiated neuron-like cells, which were repeatedly exposed during differentiation to model environmental toxicants, and we analyzed changes in sphingolipidome, cellular morphology and gene expression related to SL metabolism or neuronal differentiation. We compared these data with the results obtained in undifferentiated neural cells with progenitor-like features. As model polychlorinated organic pollutants, we used 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 3,3'-dichlorobiphenyl (PCB11) and 2,2',4,4',5,5'-hexachlorobiphenyl (PCB153). PCB153 revealed itself as the most prominent deregulator of SL metabolism and as potent toxicant during early phases of in vitro neurogenesis. TCDD exerted only minor changes in the levels of analysed lipid species, however, it significantly changed the rate of pro-neuronal differentiation and deregulated expression of neuronal markers during neurogenesis. PCB11 acted as a potent disruptor of in vitro neurogenesis, which induced significant alterations in SL metabolism and cellular morphology in both differentiated neuron-like models (differentiated NE4C and NG108-15 cells). We identified ceramide-1-phosphate, lactosylceramides and several glycosphingolipids to be the most sensitive SL species to exposure to polychlorinated pollutants. Additionally, we identified deregulation of several genes related to SL metabolism, which may be explored in future as potential markers of developmental neurotoxicity.

Transactivation and reactivation capabilities of temperature-dependent p53 mutants in yeast and human cells.

The p53 protein is a sequence-specific transcription factor controlling the expression of multiple genes and protecting cells from oncogenic transformation. In many tumors, the p53 protein is completely or partially inactivated by mutations in the p53 gene. We analyzed the transactivating activity of nine human temperature-dependent (td) p53 mutants in yeast cells. Mutations in seven of them were localized in the ß-sandwich-coding region of the p53 gene, eight p53 mutants were temperature-sensitive and the R283C mutant was cold-sensitive. Patterns of their transactivation abilities towards three different responsive elements, the extent of their temperature dependency as well as discriminativity, were considerably variable. Similarly, their capacity to become reactivated by amifostine varied from complete resistance to high sensitivity. Transactivation abilities and temperature dependency of six p53 td mutants were determined in transiently-transfected H1299 human cells and revealed substantial concordance between the activity patterns of the p53 mutants in yeast and human cells. We concluded that the td p53 mutants do not comprise a uniform group, therefore, the behavior of each mutant has to be tested individually.

Transactivation by temperature-dependent p53 mutants in yeast and human cells.

The p53 protein plays an important role in cancer prevention. In response to stress signals, p53 controls essential cell functions by regulating expression of its target genes. Full or partial loss of the p53 function in cancer cells usually results from mutations of the p53 gene. Some of them are temperature-dependent, allowing reactivation of the p53 function in certain temperature. These mutations can alter general transactivation ability of the p53 protein or they modify its transactivation only towards specific genes. We analyzed transactivation of several target genes by 23 temperature-dependent p53 mutants and stratified them into four functional groups. Seventeen p53 mutants exhibited temperature-dependency and discriminative character in human and yeast cells. Despite the differences of yeast and human cells, they allowed similar transactivation rates to the p53 mutants, thus providing evidence that functional analysis of separated alleles in yeast is valuable tool for assessment of the human p53 status.

Loss of the p53 tumor suppressor activity is associated with negative prognosis of mantle cell lymphoma.

Mantle cell lymphoma (MCL) is typified by translocation t(11;14)(q13;q32) causing upregulation of cyclin D1 and deregulation of cell cycle. The cyclin D1 activation plays a critical role in MCL pathogenesis but additional oncogenic events, such as aberrations of the ARF/MDM2/p53 pathway are also necessary for progression of the disease. We analyzed the p53 tumor suppressor in tumor tissue of 33 patients with MCL. The p53 status was determined by functional analyses in yeast (FASAY) and by cDNA sequencing. The level of the p53 protein was assessed by immunohistochemistry and immunoblotting. Loss of the p53-specific locus 17p13.3 was detected by FISH. Mutations in the p53 gene were detected in nine samples and they included eight missense mutations and one short deletion causing frame shift and premature stop codon formation in position 169. This mutation was associated with mRNA decay as revealed by sequencing of the p53 gDNA. All eight missense mutations were manifested by accumulation of the p53 protein in nuclei of tumor cells and three of them exhibited loss of the p53-specific locus 17p13.3. The p53 mutations were shown to be a negative prognostic marker in MCL.

Heavy metals induce phosphorylation of the Bcl-2 protein by Jun N-terminal kinase.

The Bcl-2 protein is one of the key components of biochemical pathways controlling programmed cell death. The function of this protein can be regulated by posttranslational modifications. Phosphorylation of Bcl-2 has been considered to be significantly associated with cell cycle arrest in the G2/M phase of the cell cycle, and with cell death caused by defects of microtubule dynamics. This study shows that phosphorylation of Bcl-2 can be induced by heavy metals due to activation of the Jun N-terminal kinase pathway that is not linked to the G2/M cell cycle arrest. Furthermore, we demonstrate that hyperphosphorylated Bcl-2 protein is a more potent inhibitor of zinc-induced cell death than its hypophosphorylated mutant form. These data suggest that regulation of Bcl-2 protein function by phosphorylation is an important part of cell responses to stress.