Expression of Acidosis‑Dependent Genes in Human Cancer Nests
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1160 MOLECULAR AND CLINICAL ONCOLOGY 2: 1160-1166 Expression of acidosis‑dependent genes in human cancer nests TOSHIHIKO FUKAMACHI1, SHUNSUKE IKEDA1, HIROMI SAITO1, MASATOSHI TAGAWA2 and HIROSHI KOBAYASHI1 1Graduate School of Pharmaceutical Sciences, Chiba University, Chuo-ku, Chiba 260-8675; 2Division of Pathology and Cell Therapy, Chiba Cancer Center Research Institute, Chuo-ku, Chiba 260-8717, Japan Received January 24, 2014; Accepted June 30, 2014 DOI: 10.3892/mco.2014.344 Abstract. Previous studies investigating cancer cells cultured glycolysis combined with impaired mitochondrial oxidative at acidic pH have shown that the expression level of ~700 genes phosphorylation (3). Organ functions may be strongly affected were more than two-fold higher than those of the cells cultured by the disruption of the pH homeostasis as all the organs in alkaline medium at pH 7.5. The aim of the present study was contain a large number of enzymes with pH‑sensitive catalytic to confirm whether these acidosis‑induced genes are expressed activity. Therefore, it can be argued that alternative metabolic in human cancer tissues. Therefore, 7 genes were selected from processes are activated under acidic conditions to compensate our previous study, which encoded interleukin 32 (IL‑32), lyso- for the decline in processes functioning at alkaline pH. somal H+ transporting ATPase, V0 subunit d2 (ATP6V0D2), When various metabolic processes are working under tumor necrosis factor receptor superfamily, member 9 different pH conditions, the efficacy of a number of inhibitors (TNFRSF9), amphiregulin, schwannoma-derived growth under acidic conditions may be different to those observed in factor (AREG), v-erb-b2 erythroblastic leukemia viral onco- conventional alkaline media. Impaired efficacy of paclitaxel, gene homolog 3 (ErbB3), PRR5-ARHGAP8 (LOC553158) and mitoxantrone and topotecan has been previously reported dimethylglycine dehydrogenase (DMGDH), and their expres- at pH 6.5 as compared to their efficacy at pH 7.4 in murine sion was examined in human clinical specimens from patients EMT6 and human MGH-U1 cells (4), and acidic conditions with cancer. In addition, the expression of the gene encoding induced daunorubicin resistance by increasing the activity of manganese superoxide dismutase (MnSOD) was examined. p-glycoprotein via p38 activation in rat prostate cancer cells (5). The specimens from patients with colon, stomach and renal Malignant pleural mesothelioma is an aggressive tumor cancer showed increased MnSOD, IL‑32, and TNFRSF9 tran- associated with asbestos exposure, and its prognosis is scripts compared to those from non-tumorous regions of the extremely poor (6). Mesothelioma shows resistance against same patients. Notably, an elevated expression of ATP6V0D2 numerous chemotherapeutic reagents (7). Our previous study was found in the specimens from patients with stomach cancer, found that statins inhibited the proliferation of mesothelioma whereas the expression was decreased in those from patients cells strongly in an acidic medium with a pH that was close with colon and renal cancer. The expression of LOC553158 to the pH of an area of cancer in vivo (8). Statins, which are was upregulated in colon and stomach cancer specimens. inhibitors of mevalonate synthesis, are prescribed for hyperlip- These results indicate that the investigation of gene expression idemia as the inhibition of mevalonate synthesis reduces blood under acidic conditions is useful for the development of novel cholesterol levels. However, the anti-cancer activity of statins cancer markers and/or chemotherapeutic targets. has not been demonstrated in vitro. Recently, clinical studies have revealed that stains are effective at attenuating the growth Introduction of cancer cells in vivo (9,10), in agreement with our previous in vitro observations at acidic pH (8). A previous study has In the central regions of solid tumors, the extracellular pH shown that the anticancer activity is caused by the inhibition falls below pH 6.5 as a consequence of lactate accumulation, of geranylgeranyl diphosphate, derived from mevalonate, indi- which is caused by hypoxic conditions produced by a lack of cated that the function of certain geranylgeranylated proteins sufficient vascularization (1,2) or an increase in tumor‑specific is essential for cell proliferation under acidic conditions (8,11). In addition to the investigations with inhibitors, our previous studies found that different signal transduction pathways func- tion under acidic environments (12,13), and that C-Terminus Correspondence to: Professor Hiroshi Kobayashi, Graduate protein of IκB-β, which is an IκB-β variant, acted as a critical School of Pharmaceutical Sciences, Chiba University, 1-8-1, Inohana, transcriptional regulatory factor at pH 6.3 only, and not at Chuo-ku, Chiba 260-8675, Japan pH 7.4 (14,15). E-mail: [email protected] These previous findings indicate that numerous proteins are functioning preferentially under low pH conditions. DNA Key words: gene expression, human cancer, acidic environments array analysis showed that the expression of ~700 genes was elevated more than two-fold in mesothelioma cells under acidic conditions compared to in cells cultured in an FUKAMACHI et al: GENE EXPRESSION IN HUMAN CANCER NESTS 1161 alkaline medium (16). Numerous genes were also found to be Table I. Primers used in the present study. strongly expressed in breast cancer cells cultured in an acidic medium (17). These gene products may be good candidate Gene name Sequence therapeutic targets and/or diagnostic markers of cancers. In the present study, the aim was to confirm whether or not the 18S rRNA F: TAGAGTGTTCAAAGCAGGCCC genes with an increased expression in cancer cells cultured in R: CCAACAAATAGAACCGCGGT acidic medium are expressed in human cancer nests. A total MnSOD F: TGA ACG TCA CCG AGG AGA AG of 8 genes with an increased expression in mesothelioma cells R: CGT GCT CCC ACA CAT CAA TC cultured under acidic conditions were selected and the expres- IL‑32 F: TCAAAGAGGGCTACCTGGAG sion was examined in human specimens from patients with R: TTTCAAGTAGAGGAGTGAGCTCTG cancer. The expression of the selected genes was demonstrated to be higher in numerous human cancer specimens compared ATP6V0D2 F: GACCCAGCAAGACTATATCAACC to those in the specimens prepared from the surrounding R: TGGAGATGAATTTTCAGGTCTTC normal areas. TNFRSF9 F: AAACGGGGCAGAAAGAAACT R: CTTCTGGAAATCGGCAGCTA Materials and methods AREG F: GGGAGTGAGATTTCCCCTGT R: AGCCAGGTATTTGTGGTTCG Human specimens from patients. Human tumor and the corresponding non-tumorous tissues were obtained from the ErbB3 F: TGCAGTGGATTCGAGAAGTG Chiba Cancer Center Tissue Bank (Chiba, Japan) and used R: GGCAAACTTCCCATCGTAGA in the study with permission from the Institutional Ethical LOC553158 F: AGCCTCCCAGAGCACAACTA Committees of Chiba Cancer Center and Chiba University. R: ATGGCCAGATCAAATTCAGC DMGDH F: GAGCTCACGGCTGGATCTAC RNA extraction from human specimens. The human tissues R: CCACCACCTGACCAGTTTCT that were stored at -80˚C were mixed with ice-cold TRI reagent (Sigma-Aldrich, St. Louis, MO, USA). After 1 min MnSOD, manganese superoxide dismutase; IL‑32, interleukin 32; on ice, the human tissues were homogenized on ice with a ATP6V0D2, lysosomal H+ transporting ATPase, V0 subunit d2; TNFRSF9, homogenizer until the pellets were broken and cell lysis was tumor necrosis factor receptor superfamily, member 9; AREG, amphiregulin, schwannoma-derived growth factor; ErbB3,v-erb-b2 erythroblastic leukemia completed. Total RNA was isolated from the lysate according viral oncogene homolog 3; LOC553158, PRR5-ARHGAP8; DMGDH, to the manufacturer's instructions for the TRI reagent. dimethylglycine dehydrogenase. Quantitative polymerase chain reaction (qPCR). Total RNA (1 µg), prepared as described above, was reverse-transcribed using ReverTra Ace (Toyobo Co., Ltd., Osaka, Japan) in a total functions, which were interleukin 32 (IL‑32), lysosomal H+ volume of 20 µl containing the random primer for 18S rRNA transporting ATPase, V0 subunit d2 (ATP6V0D2), tumor or the polyT primer for the targeted genes. qPCR amplification necrosis factor receptor superfamily, member 9 (TNFRSF9), was performed with an ABI Prism 7000 Sequence Detection amphiregulin, schwannoma-derived growth factor (AREG), System (Applied Biosystems, Foster City, CA, USA) using v-erb-b2 erythroblastic leukemia viral oncogene homolog 3 the FastStart Universal SYBR Green Master (Rox) (Roche (ErbB3), PRR5-ARHGAP8 (LOC553158) and dimethylgly- Diagnostics, Basel, Switzerland) according to the manufac- cine dehydrogenase (DMGDH), and the expression of these turer's instructions. The PCR reaction was carried out with a genes was examined in human cancer specimens. In addition, mixture containing 12.5 µl PCR Master, 7.5 µM of each sense the expression of the gene encoding manganese superoxide and antisense primer, 25 ng cDNA, and nuclease-free water dismutase (MnSOD) was examined as MnSOD has been in a total volume of 25 µl. The standard thermal profile for reported to participate in gastric and colorectal tumor metas- PCR amplification was 50˚C for 2 min, 95˚C for 10 min and tasis (19,20), although the expression of MnSOD at acidic pH 40 cycles of 95˚C for 15 sec and 60˚C for 60 sec. The primers was 1.6-fold in mesothelioma cells. The selected genes are used are shown in Table I. shown in Table II. A previous study has reported that the content of ribosomes One problem in the measurement of mRNA using qPCR per cell is ~4x106 (18), and the