Department of Phamaceutical and Biomedical Sciences, University of Georgia, Athens, Georgia 30602, USA.
Cancer Res. 2011 Mar 1;71(5):1825-35. doi: 10.1158/0008-5472.CAN-10-2736. Epub 2011 Feb 22.
Overcoming the inherent chemoresistance of pancreatic cancers remains a major goal of therapeutic investigations in this disease. In this study, we discovered a role for the human concentrative nucleoside transporter-1 (hCNT1; SLC28A1), a high-affinity pyrimidine nucleoside transporter, in determining the chemosensitivity of human pancreatic cancer cells to gemcitabine, the drug used presently as a standard of care. Compared with normal pancreas and pancreatic ductal epithelial cells, hCNT1 expression was frequently reduced in pancreatic tumors and tumor cell lines. In addition, hCNT1-mediated (3)H-gemcitabine transport was lower in pancreatic cancer cell lines and correlated with cytotoxic IC(50) estimations of gemcitabine. In contrast to gemcitabine-sensitive pancreatic cancer cell lines, MIA PaCa-2, a gemcitabine-resistant pancreatic cancer cell line, exhibited relatively restrictive, cell cycle-dependent hCNT1 expression and transport. hCNT1 translation was suppressed in the late G1-enriched MIA PaCa-2 cell population possibly in an miRNA-dependent manner, which corresponded with the lowest hCNT1-mediated gemcitabine transport during this phase. Although hCNT1 protein was induced during G1/S transition, increased hCNT1 trafficking resulted in maximal cell surface recruitment and transport-overshoot in the G2/M phase-enriched cell population. hCNT1 protein was directed predominantly to proteasomal or lysosomal degradation in S or G2/M phase MIA PaCa-2 cells, respectively. Pharmacological inhibition of hCNT1 degradation moderately increased cell surface hCNT1 expression and cellular gemcitabine transport in MIA PaCa-2 cells. Constitutive hCNT1 expression reduced clonogenic survival of MIA PaCa-2 cells and steeply augmented gemcitabine transport and chemosensitization. In addition to supporting a putative tumor suppressor role for hCNT1, our findings identify hCNT1 as a potential candidate to render drug-resistant pancreatic cancer cells amenable to chemotherapy.
克服胰腺癌固有的化疗耐药性仍然是该疾病治疗研究的主要目标。在这项研究中，我们发现人类高亲和性嘧啶核苷转运体-1（hCNT1；SLC28A1）在决定人类胰腺癌细胞对吉西他滨（目前作为标准治疗药物）的化疗敏感性方面发挥作用。与正常胰腺和胰腺导管上皮细胞相比，hCNT1 的表达在胰腺肿瘤和肿瘤细胞系中经常降低。此外，hCNT1 介导的（3）H-吉西他滨转运在胰腺癌细胞系中较低，并且与吉西他滨的细胞毒性 IC50 估计相关。与吉西他滨敏感的胰腺癌细胞系相比，MIA PaCa-2 是一种吉西他滨耐药的胰腺癌细胞系，表现出相对受限的、细胞周期依赖性的 hCNT1 表达和转运。hCNT1 翻译在富含 G1 的 MIA PaCa-2 细胞群体中被抑制，可能以 miRNA 依赖的方式进行，这与该阶段 hCNT1 介导的吉西他滨转运最低相对应。尽管 hCNT1 蛋白在 G1/S 转换期间被诱导，但增加的 hCNT1 运输导致富含 G2/M 期的细胞群体中最大的细胞表面募集和转运过冲。hCNT1 蛋白主要被导向 S 期或 G2/M 期的 MIA PaCa-2 细胞中的蛋白酶体或溶酶体降解。hCNT1 降解的药理学抑制适度增加了 MIA PaCa-2 细胞中的细胞表面 hCNT1 表达和细胞内吉西他滨转运。MIA PaCa-2 细胞中 hCNT1 的组成性表达降低了集落形成存活，并急剧增加了吉西他滨的转运和化疗增敏作用。除了支持 hCNT1 作为潜在的肿瘤抑制基因的作用外，我们的研究结果还确定 hCNT1 是使耐药性胰腺癌细胞对化疗敏感的潜在候选基因。
