Influence of tris(4-chlorophenyl)methanol (TCPM) on gap junction-mediated intercellular communication of cultured bovine granulosa cells

ATF6 knockdown decreases apoptosis, arrests the S phase of the cell cycle, and increases steroid hormone production in mouse granulosa cells

Activating transcription factor 6 (ATF6), a sensor protein located in the endoplasmic reticulum (ER) membrane, is an important factor in the ER stress signaling pathway. ER stress is known to be involved in folliculogenesis, follicular growth, and ovulation; however, the physiological function of ATF6 in mouse granulosa cells remains largely unknown. The aim of this study was to assess the role of ATF6 in mouse granulosa cells with respect to apoptosis, the cell cycle, and steroid hormone production, as well as several key genes related to follicular development, via RNA interference, immunohistochemical staining, real-time quantitative PCR, Western blotting, flow cytometry, terminal deoxynucleotidyltransferase-mediated deoxy-UTP nick end labeling (TUNEL) assay, and ELISA. Immunohistochemical staining revealed that ATF6 was extensively distributed in the granulosa cells of various ovarian follicles and oocytes in adult female mice. FSH or LH treatment significantly increased ATF6 protein levels in mouse granulosa cells. In the meantime, a recombinant plasmid was used to deplete ATF6 successfully using short hairpin RNA-mediated interference technology, which was verified at both the mRNA and protein levels. Flow cytometry and TUNEL assay analysis indicated that ATF6 depletion decreased apoptosis and arrested the S phase of the cell cycle in mouse granulosa cells. Consistent with these results, p53, caspase-3, B cell lymphoma 2 (Bcl-2)-associated X protein, CCAAT-enhancer-binding protein homologous protein, cyclin A1, cyclin B1, and cyclin D2 mRNA expression decreased, whereas Bcl-2 and glucose-regulated protein 78 kDa mRNA expression increased. Interestingly, ATF6 knockdown obviously increased progesterone and estradiol production in mouse granulosa cells. Cytochrome P450 1b1 (Cyp1b1) mRNA levels were downregulated, whereas Cyp11a1, steroidogenic acute regulatory, and Cyp19a1 mRNA levels were upregulated, in keeping with the changes in steroid hormones. Furthermore, ATF6 disruption remarkably increased insulin-like growth factor binding protein4 (Igfbp4) expression and decreased hyaluronan synthase 2 (Has2), prostaglandin-endoperoxide synthase 2 (Ptgs2), and prostaglandin F receptor (Ptgfr) expression in mouse granulosa cells, which are proteins crucial for follicular development. But, after treating with tunicamycin, the levels of Has2, Ptgs2, and Ptgfr increased relatively, whereas Igfbp4 expression decreased. Collectively, these results imply that ATF6, as a key player in ER stress signaling, may regulate apoptosis, the cell cycle, steroid hormone synthesis, and other modulators related to folliculogenesis in mouse granulosa cells, which may indirectly be involved in the development, ovulation, and atresia of ovarian follicles by affecting the physiological function of granulosa cells. The present study extends our understanding and provides new insights into the physiological significance of ATF6, a key signal transducer of ER stress, in ovarian granulosa cells.

Effects of organophosphorus pesticides and their ozonation byproducts on gap junctional intercellular communication in rat liver cell line

The effects of organophosphorus pesticides (OPs), oxons and their ozonation byproducts on gap junctional intercellular communication (GJIC) on cultured BRL cell line were investigated using scrape loading and dye transfer (SL/DT) technique. The neutral red uptake assay was used to identify the non-cytotoxic levels of diazinon, parathion and methyl-parathion applied to GJIC assay. The concentration-dependent inhibition of GJIC was observed over a range of 50-350 mg/l diazinon, parathion and methyl-parathion after 90 min incubation compared with the vehicle control. However, oxons and ozonation byproducts of OPs had no inhibition effect on GJIC at any of the concentrations tested. The inhibition of GJIC by OPs was reversible after removal of the tested pesticides followed by incubation with fresh medium. The present study suggested that the ozonation treatment could be used for the detoxification of drinking water and food crops contaminated with diazinon, parathion and methyl-parathion without formation of GJIC toxicity.

Accelerated internalization of junctional membrane proteins (connexin 43, N-cadherin and ZO-1) within endocytic vacuoles: an early event of DDT carcinogenicity

Stability of cell-to-cell interactions and integrity of junctional membrane proteins are essential for biological processes including cancer prevention. The present study shows that DDT, a non-genomic carcinogen used at a non-cytotoxic dose (1 microM), rapidly disrupted the cell-cell contacts and concomitantly induced the formation of cytoplasmic vacuoles close to the plasma membrane in the SerW3 Sertoli cell line. High-resolution deconvolution microscopy reveals that this vacuolization process was clathrin-dependent since a hyperosmotic media (0.2 M sucrose) blocked rhodamine-dextran endocytosis. In response to DDT, junctional proteins such as Cx43, N-Cadherin and ZO-1 were internalized and present in vacuoles. In Cx43-GFP transfected cells, time lapse videomicroscopy demonstrates that DDT rapidly enhanced fragmentation of the gap junction plaques and abolished the gap junction coupling without major modification of Cx43 phosphorylation status. Repeated exposure to DDT resulted in chronic gap junction coupling injury. The present results demonstrate that one of the early effect of DDT is to interfere with the plasma membrane and to perturb its function, specifically its ability to establish cell-cell junctions that are essential for tissue homeostasis and control of cell proliferation and differentiation. Such an alteration may play a specific role during carcinogenesis.

Localization of transient receptor potential ion channels in primary and motile cilia of the female murine reproductive organs

We have examined the subcellular localization of transient receptor potential (TRP) ion channels and the potential sensory role of cilia in murine female reproductive organs using confocal laser scanning microscopy analysis on ovary and oviduct tissue sections as well as on primary cultures of follicular granulosa cells. We show that the Ca2+ permeable cation channel, polycystin-2, as well as polycystin-1, a receptor that forms a functional protein complex with polycystin 2, distinctively localize to primary cilia emerging from granulosa cells of antral follicles in vivo and in vitro. Both polycystins are localized to motile oviduct cilia and this localization is greatly increased upon ovulatory gonadotropic stimulation. Further, the Ca2+ permeable cation channel, TRP vaniloid 4 (TRPV4), localizes to a sub-population of motile cilia on the epithelial cells of the ampulla and isthmus with high intensity in proximal invaginations of the epithelial folds. These observations are the first to demonstrate ciliary localization of TRP ion channels and their possible receptor function in the female reproductive organs. We suggest that polycystins 1 and 2 play an important role in granulosa cell differentiation and in development and maturation of ovarian follicles. In the oviduct both TRPV4 and polycystins could be important in relaying physiochemical changes in the oviduct upon ovulation.