Dnajb8, a Member of the Heat Shock Protein 40 Family Has a Role in the Tumor Initiation and Resistance to Docetaxel but Is Dispensable for Stress Response

Cancer stem-like cells (CSCs)/cancer-initiating cells (CICs) are defined by their abilities of tumor initiation, self-renewal and differentiation. In a previous study, we showed by gene knockdown using siRNA and gene overexpression experiments that Dnaj (Hsp40) homolog, subfamily B, member 8 (DNAJB8), a role in the maintenance, of renal cell carcinoma CSCs/CICs. In the present study, we established Dnajb8 knockout (KO) renal cell carcinoma (RCC) line cells (RenCa cells) and analyzed the cells to confirm the function of Dnajb8 in RCC CSCs/CICs. Dnajb8 KO cells showed reduced ratios of side population cells and reduced sphere forming ability. An in vivo single cell tumor initiation assay revealed that the numbers of CSCs/CICs were 3 in 4 wild-type RenCa cells and 1 in 4 Dnajb8 KO cells. Dnajb8 KO cells showed sensitivity to Docetaxel. On the other hand, Dnajb8 KO cells did not show any sensitivities to stresses including low pH, low glucose, heat shock and sensitivity to cisplatin. The results indicate that Dnajb8 has a role in tumor initiation, side population ratio and sphere formation but it is dispensable for stress responses.

癌干细胞样细胞（Cancer stem-like cells, CSCs）/癌起始细胞（cancer-initiating cells, CICs）以具备肿瘤起始、自我更新及分化能力为核心定义。既往研究中，本团队通过小干扰RNA（siRNA）介导的基因敲低实验与基因过表达实验，证实了DnaJ（热休克蛋白40, Hsp40）同源物B亚家族成员8（DNAJB8）在肾细胞癌（renal cell carcinoma, RCC）CSCs/CICs的维持中发挥作用。本研究构建了Dnajb8基因敲除（knockout, KO）的肾细胞癌（RCC）细胞系（RenCa细胞），并对该细胞系进行分析以验证Dnajb8在肾细胞癌CSCs/CICs中的功能。结果显示，Dnajb8基因敲除细胞的侧群细胞（side population cells）比例降低，且成球能力显著减弱。体内单细胞肿瘤起始实验表明，每4个野生型RenCa细胞中存在3个具有肿瘤起始能力的CSCs/CICs，而每4个Dnajb8基因敲除细胞中仅存在1个。此外，Dnajb8基因敲除细胞对多西他赛（Docetaxel）表现出敏感性；与之相反，该细胞对低pH、低糖、热休克等应激刺激及顺铂（cisplatin）均未显现出敏感性。上述结果证实，Dnajb8在肿瘤起始、侧群细胞比例维持及成球能力维持中具有关键作用，但并非细胞应激响应所必需。