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During the screening of natural chemicals that can reverse multidrug resistance in human A549 lung cancer cells resistant to etoposide (A549RT-eto), we discovered that Feroniellin A (FERO), a novel furanocoumarin, shows toxicity toward A549RT-eto cells in a dose- and time-dependent manner. FERO reduced the expression of NF-κB, leading to downregulation of P-glycoprotein (P-gp), encoded by MDR1, which eventually sensitized A549RT-eto cells to apoptosis. FERO specifically diminished transcription and promoter activity of MDR1 but did not inhibit the expression of other multidrug resistance genes MRP2 and BCRP. Moreover, co-administration of FERO with Bay11-7802, an inhibitor of NF-κB, accelerated apoptosis of A549RT-eto cells through decreased expression of P-gp, indicating that NF-κB is involved in multidrug resistance. Conversely, addition of Z-VAD, a pan-caspase inhibitor, blocked FERO-induced apoptosis in A549RT-eto cells but did not block downregulation of P-gp, indicating that a decrease in P-gp expression is necessary but not sufficient for FERO-induced apoptosis. Interestingly, we found that FERO also induces autophagy, which is characterized by the conversion of LC3 I to LC3 II, induction of GFP-LC3 puncta, enhanced expression of Beclin-1 and ATG5, and inactivation of mTOR. Furthermore, suppression of Beclin-1 by siRNA reduced FERO-induced apoptosis in A549RT-eto cells and activation of autophagy by rapamycin accelerated FERO-induced apoptosis, suggesting that autophagy plays an active role in FERO-induced apoptosis. Herein, we report that FERO reverses multidrug resistance in A549RT-eto cells and exerts its cytotoxic effect by induction of both autophagy and apoptosis, which suggests that FERO can be a useful anticancer drug for multidrug-resistant lung cancer.

Despite efforts to develop efficient chemotherapeutic drug strategies to treat cancer, acquired drug resistance is a commonly encountered problem. In the present study, to investigate this phenomenon, human A549 lung cancer cells resistant to the topoisomerase inhibitor etoposide (A549RT‑eto) were used and compared with A549 parental cells. A549RT‑eto cells demonstrated increased resistance to etoposide‑induced apoptosis when compared with A549 parental cells. Notably, A549RT‑eto cells were observed to exhibit greater levels of histone deacetylase 4 (HDAC4), phospho‑Stat1 and P‑glycoprotein [P‑gp; encoded by the multidrug resistance 1 (MDR1) gene], compared with A549 cells. To address whether HDAC4 protein is involved in etoposide resistance in A549 cells, A549RT‑eto cells were treated with trichostatin A (TSA; an HDAC inhibitor) during etoposide treatment. The combined treatment was demonstrated to enhance etoposide‑induced apoptosis and reduce expression levels of HDAC4, P‑gp and phospho‑Stat1. In addition, the suppression of Stat1 with siRNA enhanced etoposide‑induced apoptosis and reduced the expression levels of HDAC4 and P‑gp, suggesting that Stat1 is essential in the regulation of resistance to etoposide, and in the upregulation of P‑gp. Notably, TSA treatment reduced P‑gp transcript levels but Stat1 siRNA treatment did not, suggesting that P‑gp is regulated by HDAC at the transcriptional level and by Stat1 at the post‑transcriptional level. These results suggest that the upregulation of Stat1 and HDAC4 determines etoposide resistance through P‑gp expression in human A549 lung cancer cells.

Abstract. Cancer upregulated gene (CUG) 2, as a novel oncogene, has been predominantly detected in various cancer tissues, such as ovary, liver, lung and colon. We recently showed that CUG2 elevates STAT1 activity, leading to resistance to infection by oncolytic vesicular stomatitis virus. To investigate a possible role for CUG2-induced activation of STAT1 in oncogenesis, we first established a colon cancer cell line stably expressing CUG2 (Colon26L5-CUG2). Colon26L5-CUG2 exhibited higher levels not only in phosphorylation of STAT1, but also phosphorylation of Jak1/Tyk2 compared to that of the control (Colon26L5-Vec) cell line. Inhibition of Akt or ERK activity reduced phosphorylation of STAT1 in Colon26L5-CUG2 cells whereas inhibition of p38 MAPK did not significantly decrease levels of STAT1 phosphorylation, indicating that cell proliferation signals may be involved in CUG2-mediated activation of STAT1. Suppression of STAT1 expression diminished cell migration and wound healing compared to the control cells. In addition, since CUG2 expression conferred resistance to DNA damage caused by doxorubicin treatment, we investigated whether STAT1 is involved in resistance to doxorubicininduced cell death. We found that STAT1 was not activated in Colon26L5-Vec cells while phosphorylated STAT1 was maintained in Colon26L5-CUG2 cells during doxorubicin treatment. Furthermore, suppression of STAT1 expression sensitized Colon26L5-CUG2 cells to doxorubicin-induced apoptosis whereas the control cells exhibited resistance to doxorubicin. Taken together, our results suggest that CUG2 enhances metastasis and drug resistance through STAT1 activation, which eventually contributes to tumor progression. IntroductionTo discover new genes that play a crucial role in common tumorigenesis regardless of tissue origin, we analyzed commonly upregulated unknown genes in 242 normal and 300 tumor samples originating from 11 different tissues using the Affymetrix gene chip system. An Affymetrix fragment, later named cancer upregulated gene (CUG) 2 was identified as a candidate gene that is commonly upregulated in various tumor tissues such as ovary, liver, lung and colon. This CUG2 was mapped to chromosome 6q22.32; it spans ~8.5 kb with a three-exon structure and encodes a 88-amino acid polypeptide (1). Further study has revealed that CUG2 is a new component of centromere required for a proper kinetochore function during cell division (2). Of interest, CUG2 has been shown to harbor an oncogenic effect in a transplanted model using NIH3T3 cells expressing CUG2, in a manner similar to Ras (1). Although CUG2 overexpression leads to activated Ras and MAPKs including p38 MAPK, which eventually facilitates oncolytic reoviral replication (3), CUG2 contrastingly provides resistance to oncolytic vesicular stomatitis virus infection through activation of STAT1 as shown in our recent study (4).Although STAT1 is well known as a master transcription factor for IFN-related intracellular signaling, leading to antiviral activity, several lines of evidence hav...

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Overexpression of HIF-1α, a transcription factor responsive to hypoxia, is frequently observed in malignant tumors, which sometimes show resistance to chemotherapy and radiation therapy. Consequently, decrease of HIF-1α through virotherapy offers a logical strategy for the treatment of aggressive tumors. In this study, we found that infection with the oncolytic H-1 parvovirus decreased HIF-1α protein levels in pancreatic cancer cells under CoCl2 or hypoxia. The H-1 virus-induced decrease of HIF-1α was regulated by a proteasome-mediated pathway. Suppression of VHL, an E3 ligase and a critical regulator of HIF-1α, or enforced expression of UCP, an E2 ubiquitin-conjugating enzyme, failed to inhibit the H-1 virus-induced decrease of HIF-1α. Furthermore, siRNA-mediated suppression of RACK1, another regulator of HIF-1α, did not prevent H-1 viral infection from lowering HIF-1α protein levels. Although decrease of HIF-1α was observed after H-1 viral infection, constitutive expression of HIF-1α limited H-1 viral replication. After combined treatment with H-1 parvovirus and YC-1, an inhibitor of HIF-1α, the apoptosis of pancreatic cancer cells was greater than after treatment with H-1 virus alone or YC-1 alone. Accordingly, we propose that H-1 parvovirus could be used with YC-1 as a potential therapeutic agent against aggressive tumors exhibiting hypoxia and increased levels of HIF-1α.

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