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Abbreviations: CK1, casein kinase 1; GSK-3β, glycogen synthase kinase-3β; PAUF, pancreatic adenocarcinoma up-regulated factor; PKA, protein kinase A; sh-RNA, short hairpin-RNA; TCF/LEF, T cell factor/lymphocyte enhancer factor

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...

As we have recently found a novel oncogene, the cancer-upregulated gene 2 (CUG2), which was elevated in a variety of tumor tissues such as the ovary, liver, lung and pancreas, we examined whether reovirus could efficiently induce cytolysis in cancer cells expressing CUG2 and thus be used as a potential cancer therapeutic agent. In this study, we describe experiments in which we use reovirus to treat NIH3T3 cells stably expressing either CUG2 (NIH-CUG2) or vector only (NIH-Vec). NIH-CUG2 cells readily support reoviral proliferation and undergo apoptosis, whereas NIH-Vec cells are highly resistant to reoviral infection and virusinduced apoptosis. This notable result may be explained by the observation that CUG2 expression inhibits PKR activation, leading to reoviral proliferation in nonpermissive NIH3T3 cells. Furthermore, reovirus infection results in almost complete regression of tumorgenic NIH-CUG2 cells in transplanted nude mice. As we found that CUG2 enhances activation of MAPK (ERK, JNK and p38), Src kinase and Ras, we examined whether CUG2 confers reoviral replication independent of the Ras or p38 MAPK signaling pathway. From these experiments we found that either inhibition of p38 MAPK or Ras blocks reoviral proliferation even in the presence of CUG2 but inhibition of ERK, JNK and Src kinase does not, indicating that activation of p38 MAPK and Ras has critical roles in reoviral replication in CUG2-expressing tumor cells. Accordingly, we propose that reovirus can be useful in the treatment of transformed cells expressing CUG2, which is commonly detected in various tumor tissues.