Autophagy Attenuates MnCl2-induced Apoptosis in Human Bronchial Epithelial Cells.

OBJECTIVE: To investigate the role of autophagy in MnCl2-induced apoptosis in human bronchial epithelial 16HBE cells. METHODS: Cell proliferation was measured by MTT assay. Mitochondrial membrane potential (MMP) and apoptosis were measured by flow cytometry. Autophagic vacuoles were detected by fluorescence microscopy. Cellular levels of apoptosis and autophagy-related proteins were measured by western blotting. RESULTS: 16HBE cell proliferation was inhibited by MnCl2 in a dose- and time-dependent manner. MnCl2-induced 16HBE cell growth inhibition was related to MMP depolarization prior to the induction of apoptosis. Our data revealed that MnCl2-induced apoptosis in 16HBE cells was mediated by decreased expression of Bcl-2 and increased levels of cleaved caspase-3. It was observed that when we exposed 16HBE cells to MnCl2 in a dose-dependent manner, the formation of autophagic vacuoles and the levels of LC-3B-II were elevated. RNA interference of LC3B in these MnCl2-exposed cells demonstrated that MMP loss and apoptosis were enhanced. Additionally, the pan-caspase inhibitor Z-VAD-FMK increased the cellular levels of Bcl-2 and decreased apoptosis, but did not affect the cellular levels of LC3B in MnCl2-treated 16HBE cells. CONCLUSION: MnCl2 dose- and time-dependently inhibits 16HBE cell proliferation and induces MMP loss and apoptosis. Autophagy acts in a protective role against MnCl2-induced apoptosis in 16HBE cells.

Antigen-subtracted 2-DE/MS strategy, a novel proteomic analysis platform.

In the present study, we developed a novel proteomic research strategy named antigen-subtracted 2-DE/MS strategy and applied it to comparative proteomic analysis of anti-benzo(a)pyrene-7,8-dihydrodiol-9,10-epoxide-transformed human bronchial epithelial cell line (16HBE-C) and its parental cell line (16HBE) G0/G1 cells. Following pre-purification by ammonium sulfate precipitation, rabbit antibodies against 16HBE G0/G1 cells were coupled with protein A/G PLUS-agarose under the maximal coupling rate of about 50%. The agarose-antibody complex was then used in immunoprecipitation known as antigen subtraction. When the mass ratio of antibody to the sample was 2.5-3:1, the subtraction rates for 16HBE and 16HBE-C G0/G1 cell proteins were 44 and 34%, respectively. Both subtracted and unsubtracted samples were then subjected to the 2-DE resolution. In 16HBE-subtracted 2-DE maps, 315 protein spots were subtracted and 49 new protein spots were detected, whereas in 16HBE-C-subtracted 2-DE maps, 287 protein spots were subtracted and 33 new protein spots were detected. Taken together, antigen subtraction results in 65 new protein spots being allowed to be detected, therefore, makes it possible to get more information of the samples. Finally, 4 protein spots only detected in 16HBE-C-subtracted 2-DE maps were analyzed by the Q-TOF MS/MS, and successfully identified as U6 snRNA-associated Sm-like protein LSm3, 60S acidic ribosomal protein P1, Peroxiredoxin-6 and 60S acidic ribosomal protein P2. These proteins are involved in carcinogenesis, oxidation stress and protein synthesis. In conclusion, the antigen-subtracted 2-DE/MS strategy could reduce the complexities of protein samples and therefore, improve the resolution for the sample analysis.

Diethyl sulfate induced Cdk2-dependent centrosome amplification in CHL cells.

The function of centrosome that serves as the main microtubule organizing center is essential to ensure the genomic integrity during the cell division cycle. Centrosome abnormalities are frequently observed in many tumors and cells exposed to genotoxic agents. Here, we investigated the centrosome abnormalities induced by diethyl sulfate (DES) in Chinese hamster lung (CHL) fibroblasts and the underlying molecular mechanisms. Our results showed that DES exposure at 0.3, 1 and 3mM for 48 h caused centrosome amplification in a dose dependent manner. This effect was associated with transient S and G2/M phase delay and up-regulating of Cdk2, Cyclin A expressions. Furthermore, inhibition of Cdk2 activities reversed the centrosome amplification induced by DES. These results reveal that centrosome is one of the key subcellular targets of DES. Centrosome abnormalities might be important mechanisms behind the aneuploidy induction and carcinogenicity of DES.

Comparative proteomic analysis of anti-benzo(a)pyrene-7,8-dihydrodiol-9,10-epoxide-transformed and normal human bronchial epithelial G0/G1 cells.

In the present study, we investigated the proteomic profiling of anti-benzo(a)pyrene-7,8-dihydrodiol-9,10-epoxide (anti-BPDE)-transformed human bronchial epithelial cell line (16HBE-C) and its parental cell line (16HBE) G0/G1 cells. Differential analysis of proteomic profiling indicated that 67 polypeptides were down-regulated and 77 polypeptides were up-regulated in 16HBE-C G0/G1 cells compared to 16HBE G0/G1 cells. Then 16 differentially expressed protein spots were analyzed with Q-TOF MS/MS. Of these spots, 3 down-regulated polypeptides were identified as sorcin, small ubiquitin-related modifier 2 precursor and eukaryotic translation initiation factor 5A-1, and 9 up-regulated polypeptides were identified as calmodulin, myosin light polypeptide 6, eukaryotic translation initiation factor 6, proliferating cell nuclear antigen (PCNA), tumor protein D52 (TPD52), superoxide dismutase [Cu-Zn], prohibitin, nuclear protein Hcc-1 and vimentin. These proteins are involved in cell proliferation, protein synthesis, signal transduction and carcinogenesis. Western blotting analysis verified the increased expression levels of PCNA and TPD52 in 16HBE-C G0/G1 cells. Based on the clues from proteomic analysis, the migration and invasion capabilities of 16HBE-C and 16HBE cells were tested. The results indicated that 16HBE-C cells showed much higher migration and invasion capabilities than 16HBE cells, and moreover, the suppression of TPD52 by RNAi resulted in significant decrease of migration and invasion capabilities of 16HBE-C cells. These results will be valuable for further investigating and understanding the mechanisms underlying BaP-induced carcinogenesis.

Claspin is involved in S-phase checkpoint induced by benzo(a)pyrene in 16HBE cells.

Environmental carcinogen benzo(a)pyrene (BaP) can damage DNA by forming bulky adducts that are degraded further to DNA strand breaks, thus contributing to induce DNA damage checkpoint response. Claspin is a critical checkpoint protein in response to multiple forms of genotoxic stress including UV, IR and hydroxyurea (HU). In the present study we have investigated the role of human Claspin in the DNA damage checkpoint elicited by BaP in 16HBE cells. We observed that Claspin levels are increased in a time-dependent manner in response to S-phase arrest induced by BaP. In addition, the levels of phosphorylation of Chk1 on S345 were increased, but the levels of Cdc25A were decreased after treatment with BaP. Inhibition of Claspin expression (siRNA) attenuated the effect of BaP on S-phase arrest and abrogated the activation of Chk1 and degradation of Cdc25A in response to BaP. Taken together, these data imply that Claspin plays an important role in S-phase checkpoint induced by BaP, and it participates in the activation of Chk1 and Cdc25A in this checkpoint pathway.

Manganese chloride-induced G0/G1 and S phase arrest in A549 cells.

In the present study, we investigated the effects of manganese chloride (MnCl2) on cell cycle progression in A549 cells used as a model of Mn-induced lung toxicity. Cells were treated with various concentrations of MnCl2 (0, 0.01, 0.1, 0.5, 1.0 or 2.0 mM) for 24, 48 or 72 h. Cell proliferation was determined with MTT assay and mitotic index measurement and apoptosis was measured by flow cytometer. The results showed that MnCl2 inhibited A549 cells proliferation in a dose- and time-dependent manner, and induced apoptosis in A549 cells. When G0/G1 cells obtained by serum starvation were incubated with 0.5 mM of MnCl2 in the presence of 10% serum for several time intervals, the disruption of cell cycle progression was observed. The G0/G1 arrest was induced by MnCl2 treatment at 16 h and the arrest maintained for 8 h. Following the G0/G1 arrest, MnCl2 blocked the cells at S phase at 28 h and the S phase arrest maintained for at least 4 h. And moreover, proteasome inhibitor MG132 was able to prolong the duration of G0/G1 arrest induced by MnCl2 treatment. Results of western blotting assay revealed that cellular Cdk4, Cdk2 and phospho-Cdk2 (Thr160) levels decreased in manganese-treated cells at both 20 and 28 h. In addition, the decreasing of Cyclin A level and the increasing of p53 and WAF1/p21 were also induced by MnCl2 treatment at 20 h. The expression of Cyclin D1, Cyclin E and Cdc25A proteins was not altered in manganese-treated cells at both 20 and 28 h. Our results indicate that MnCl2 orderly induces G0/G1 and S phase arrest in A549 cells, the decreasing of Cdk4, Cdk2 and Cyclin A, and the increasing of p53 and Cdks inhibitor WAF1/p21 might be responsible for the G0/G1 arrest, and the decreasing of Cdk4 and Cdk2 levels for the S phase arrest.