Tsubouchi Kento, Minami Kazumasa, Hayashi Naoki, Yokoyama Yuhki, Mori Seiji, Yamamoto Hirofumi, Koizumi Masahiko
Department of Medical Physics and Engineering, Division of Health Sciences, Graduate School of Medicine, Osaka University, 1-7 Yamadaoka, Suita, Osaka 565-0871, Japan.
Department of Molecular Pathology, Division of Health Sciences, Graduate School of Medicine, Osaka University, 1-7 Yamadaoka, Suita, Osaka 565-0871,Japan.
J Radiat Res. 2017 Nov 1;58(6):816-826. doi: 10.1093/jrr/rrx033.
Resistance to chemoradiotherapy is one reason for the increased recurrence rate of pancreatic cancer after these therapies. These cells change the expression levels of several proteins, such as epithelial-mesenchymal transition (EMT), while acquiring the chemo- or radio-resistance. In this study, we focused on CD44, a pancreatic cancer stem cell marker. CD44 has isoforms with different functions: standard isoform (CD44s) and several variant isoforms (CD44v). However, little is known about the roles of these isoforms after ionizing irradiation. The purpose of this study was to investigate the role of CD44 isoforms in radioresistance of pancreatic cancer cells. AsPC-1 (a human pancreatic cancer cell line) was irradiated with 4 MV X-rays. The mRNA and protein levels of CD44s were strongly upregulated, dose dependently, compared with CD44v after irradiation. Thus, we further investigated CD44s at the point of cell proliferation. We evaluated cell proliferation and survival, using CD44s knockdown cells. CD44s knockdown did not change the proliferation rate for up to 72 h after the irradiation, but decreased cell viability in the colony formation assay. As one of the reasons for these effects, we found downregulation of phosphorylated extracellular signal-regulated kinase (Erk; which is involved with cell proliferation) by CD44s knockdown, time dependently. Moreover, radiation-induced EMT-like expression changes were detected and suppressed by CD44s knockdown. In conclusion, our work demonstrated that CD44 standard isoform was especially upregulated after high-dose X-ray irradiation in several isoforms of CD44 and contributed to longer-term cell survival after the irradiation through the maintenance of Erk phosphorylation and radiation-induced EMT.
放化疗耐药是胰腺癌经这些治疗后复发率升高的原因之一。这些细胞在获得放化疗耐药性的同时，会改变几种蛋白质的表达水平，如上皮-间质转化（EMT）相关蛋白。在本研究中，我们聚焦于胰腺癌干细胞标志物CD44。CD44有功能不同的异构体：标准异构体（CD44s）和几种变异异构体（CD44v）。然而，关于这些异构体在电离辐射后的作用知之甚少。本研究的目的是探讨CD44异构体在胰腺癌细胞放射抗性中的作用。用4 MV X射线照射AsPC-1（一种人胰腺癌细胞系）。与照射后的CD44v相比，CD44s的mRNA和蛋白水平呈剂量依赖性强烈上调。因此，我们在细胞增殖方面进一步研究了CD44s。我们使用CD44s敲低细胞评估细胞增殖和存活情况。CD44s敲低在照射后长达72小时内未改变增殖率，但在集落形成试验中降低了细胞活力。作为这些效应的原因之一，我们发现CD44s敲低会时间依赖性地下调磷酸化细胞外信号调节激酶（Erk，其与细胞增殖有关）。此外，检测到辐射诱导的EMT样表达变化，并被CD44s敲低所抑制。总之，我们的研究表明，在CD44的几种异构体中，CD44标准异构体在高剂量X射线照射后尤其上调，并通过维持Erk磷酸化和辐射诱导的EMT促进照射后细胞的长期存活。
