Part II-mechanism of adaptation: A549 cells adapt to high concentration of nitric oxide through bypass of cell cycle checkpoints

High nitric oxide-adapted head and neck cancer cell lines demonstrate altered autophagy and apoptosis

Background/purpose

Autophagy is an intracellular degradative process occurring under stressful conditions. Nitric oxide (NO), a free radical, regulates autophagy and apoptosis in several cancers. However, the effect of head and neck squamous cell carcinoma (HNSCC) cell adaptation to high nitric oxide (HNO) on autophagy remains unknown. We investigated the autophagy and apoptotic changes in the HNO-adapted HNSCC cell lines.

Materials and methods

Isogenic primary HNSCC (HN18/HN30) and metastatic (HN17/HN31) cell lines were evaluated. The cells were induced with 1, 2, 3 and 4 mM DEA-NONOate, an NO donor, for 72 h and assessed for cell viability by MTT assay. "HNO-adapted cells" were defined when the cell viability in the treatment group was <10%. The surviving cells were re-treated with HNO to confirm their adaptation. HNO-adapted cells were quantified for apoptosis using flow cytometry. Autophagic structures (autophagosomes) and proteins (LC3A/B and LC3B-II) were investigated using transmission electron and confocal microscopy, respectively.

Results

HNO-adapted concentration for HN18, HN17, HN30 and HN31 cells was 3, 2, 4 and 4 mM, respectively. The HNO-adapted HN18 cells demonstrated a significantly increased apoptotic percentage, whereas no significant apoptotic change was detected in the HNO-adapted HN17, HN30 and HN31 cells compared with the parent cells. Autophagosomes were widely observed across the HNO-adapted cells. Moreover, LC3A/B and LC3B-II proteins were increased in all HNO-adapted cells.

Conclusion

Our results demonstrate that apoptosis and/or autophagy are increased during HNO adaptation in HNSCC cell lines.

DNA Methylation in Human Breast Cancer Cell Lines Adapted to High Nitric Oxide

BACKGROUND

Nitric oxide (NO) exposure has been suggested to cause alterations in DNA methylation in breast cancer. We investigated the effect of NO on DNA methylation of promoters in cell lines of breast cancer.

MATERIAL AND METHODS

The methylation status of the promoters of breast cancer 1 (BRCA1), deleted in colon cancer (DCC), Ras-association domain family 1A (RASSF1A), O⁶-methylguanine-DNA methyltransferase (MGMT), and secreted frizzled related protein 1 (SFRP1) were analyzed in the parental and high nitric oxide-adapted cell lines of breast cancer using Illumina MiSequencing.

RESULTS

Methylation of RASSF1A promoter in BT-20-HNO (74.7%) was significantly higher than that in BT-20 cells (72%) (p<0.05), whereas in MCF-7-HNO cells, methylation of MGMT promoter was found to have significantly decreased as compared to its parental cell line (45.1% versus 50.1%; p<0.0001). Promoter methylation of SFRP and DCC was elevated in T-47D-HNO relative to its parent cell line (p<0.05).

CONCLUSION

Similarly to the double-edged effects of NO on tumorigenesis, its epigenetic effects through DNA methylation are diverse and contradictory in breast cancer.

Expression of cross-tolerance to a wide range of conditions in a human lung cancer cell line after adaptation to nitric oxide

Previously, we have shown that A549, a human lung adenocarcinoma, can be adapted to nitric oxide (NO^●). NO^● is a nitrogen-based free radical that is synthesized by a family of enzymes known as nitric oxide synthases. NO^● has been shown to be overexpressed in patient populations of different cancers. In addition, it has been observed that patients who express high levels of nitric oxide synthases tend to have poorer clinical outcomes than those with low levels of expression. The original cell line A549 (parent) and the adapted A549-HNO (high nitric oxide) cell line serve as a useful model system to investigate the role of NO^● in tumor progression and prognosis. We have previously shown that the A549-HNO-adapted cells grow aggressively when compared to A549-parent cells. Furthermore, we have shown that the A549-HNO-adapted cells exhibit a higher percentage of cell viability when exposed to ultraviolet and X-ray radiation than the A549-parent cells. Cancer patients who develop resistance to one treatment often become resistant to other previously unencountered forms of treatment. This phenomenon is known as cross-tolerance. To determine whether NO^● is a potential cross-tolerance causing agent, we have expanded our research by conducting parallel studies to a variety of other agents and conditions beyond radiation and ultraviolet exposure. We exposed both cell lines to varying levels of chemotherapeutic drugs (taxol and doxorubicin), temperature, pH, calcium chloride, cadmium chloride, copper chloride, sodium chloride, ferrous chloride, and sodium-R-lipoic acid. Our results show that the A549-HNO cells exhibit greater viability than the A549-parent cells when exposed to each of the various conditions. Therefore, NO^● is one potential driving force that can make tumor cells exhibit cross-tolerance.

Genetics of Adrenocortical Development and Tumors

This article links the understanding of developmental physiology of the adrenal cortex to adrenocortical tumor formation. Many molecular mechanisms that lead to formation of adrenocortical tumors have been discovered via next-generation sequencing approaches. The most frequently mutated genes in adrenocortical tumors are also factors in normal adrenal development and homeostasis, including those that alter the p53 and Wnt/β-catenin pathways. In addition, dysregulated protein kinase A signaling and ARMC5 mutations have been identified as key mediators of adrenocortical tumorigenesis. The growing understanding of genetic changes that orchestrate adrenocortical development and disease pave the way for potential targeted treatment strategies.

Nitric oxide: Friend or Foe in Cancer Chemotherapy and Drug Resistance: A Perspective

A successful treatment of cancers in the clinic has been difficult to achieve because of the emergence of drug resistant tumor cells. While various approaches have been tried to overcome multi-drug resistance, it has remained a major road block in achieving complete success in the clinic. Extensive research has identified various mechanisms, including overexpression of P-glycoprotein 170, modifications in activating or detoxification enzymes (phase I and II enzymes), and mutation and/or decreases in target enzymes in cancer cells. However, nitric oxide and/or nitric oxide-related species have not been considered an important player in cancer treatment and or drug resistance. Here, we examine the significance of nitric oxide in the treatment and resistance mechanisms of various anticancer drugs. Furthermore, we describe the significance of recently reported effects of nitric oxide on topoisomerases and the development of resistance to topoisomerase-poisons in tumor cells.

A549 cells adapted to high nitric oxide show reduced surface CEACAM expression and altered adhesion and migration properties

The migration and adhesion properties of tumors affect their metastatic rate. In the present study, we investigated carcinoembryonic antigen-related cell adhesion molecule (CEACAM) 1, 5, and 6 expression in high nitric oxide (HNO)-adapted lung cancer cells compared to parent cells. We observed high transcript levels of CEACAM 1 (4S, 4L), CEACAM 5, and CEACAM 6 in HNO cells compared to parent cells. However, the surface expression was low in HNO cells. Interestingly, the intracellular protein levels were high for these three CEACAMs. We confirmed these results with immunohistochemical experiments. Further, the adhesion and migration assays showed reduced clumping in HNO-adapted A549 (A549-HNO) cells and faster migration rates, respectively. These results document the altered adhesion and migration properties of cells adapted to HNO. Further, our studies also indicate a dynamic regulation of CEACAM protein expression and surface transport in HNO cells.

Part I-mechanism of adaptation: high nitric oxide adapted A549 cells show enhanced DNA damage response and activation of antiapoptotic pathways

Our previous studies demonstrate that A549, a human lung adenocarcinoma line, could be adapted to the free radical nitric oxide (NO([Symbol: see text])). NO([Symbol: see text]) has been shown to be overexpressed in human tumors. The original cell line, A549 (parent), and the newly adapted A549-HNO (which has a more aggressive phenotype) serves as a useful model system to study the role of NO([Symbol: see text]) in tumor biology. It is well known that DNA damage response (DDR) is altered in cancer cells and NO([Symbol: see text]) is known to cause DNA damage. Modulations in molecular mechanisms involved in DNA damage response in A549-HNO cells can provide better insights into the enhanced growth behavior of these cells. Thus, here, we carried out a series of time course experiments by treating A549 and A549-HNO cells with NO([Symbol: see text]) donor and examining levels of proteins involved in the DDR pathway. We observed induced expression of key components of DDR pathway in A549-HNO cells. The HNO cells showed sustained expression of key proteins involved in both nonhomologous end joining (NHEJ) and homologous recombination pathways, whereas parent cells only expressed low levels of NHEJ pathway proteins. Further with prolonged NO([Symbol: see text]) exposure, ATR, Chk1, and p53 were activated and upregulated in HNO cells. Activation of p53 results in inhibition of apoptosis through induced Mcl1 expression. It also leads to cell cycle modulation. Interestingly, several reports show that cancer stem cells have enhanced expression of proteins involved in DNA damage response and also activated an antiapoptotic response. Our results here suggest that our HNO adapted A549 cells have increased activation of DNA damage response pathway proteins which can lead to better DNA repair function. Enhanced DDR leads to activation of antiapoptosis response and modulation in the cell cycle which may lead to better survival of these cells under harsh conditions. Thus, our present investigation further supports the hypothesis that HNO exposure leads to survival of these cells.