Department of Oncology-Pathology, Cancer Centre Karolinska, Karolinska Institutet, Stockholm, Sweden.
Exp Cell Res. 2013 Mar 10;319(5):600-11. doi: 10.1016/j.yexcr.2012.12.006. Epub 2012 Dec 13.
The molecular chaperone Hsp90 is required to maintain the activity of many signaling proteins, including members of the JAK/STAT and the PI3K pathways. Inhibitors of Hsp90 (Hsp90-Is) demonstrated varying activity against multiple myeloma (MM) in clinical trials. We aimed to determine which signaling pathways that account for the differential sensitivity to the Hsp90-I 17DMAG on a panel of MM cell lines and freshly obtained MM cells. Three CD45(+) cell lines with an activated JAK/STAT3 pathway were sensitive to 17DMAG and underwent prominent apoptosis upon treatment, while the majority of CD45(-) cell lines, that were dependent on the activated PI3K pathway, were more resistant to the drug. Culturing the most resistant cell line, LP1, in the presence of IL-6 resulted in up-regulation of CD45 and pSTAT3, and sensitized to 17DMAG-induced apoptosis, primarily in the induced CD45(+) sub-population of cells. The high CD45 expressers among primary myeloma cells also expressed significantly higher levels of pSTAT3, as compared to the low CD45 expressers. Ex vivo treatment of primary myeloma cells with 17DMAG resulted in a stronger caspase3 activation in tumor samples with the prevalence of high CD45 expressers. STAT3 activity was efficiently inhibited by Hsp90-Is in both cell lines and primary cells suggesting an importance of STAT3 inactivation for the pro-apoptotic effects of HSP90-Is. Indeed, over-expression of STAT3C, a variant with an increased DNA binding activity, in U266 cells protected them from 17DMAG-induced cell death. The down-regulation of the STAT3 target gene Mcl-1 at both the mRNA and protein levels following 17DMAG treatment was significantly attenuated in STAT3C-expressing cells, and transient over-expression of Mcl-1 protected U266 cells from 17DMAG-induced cell death. The finding that CD45(+) MM cells with an IL-6-activated JAK/STAT3 pathway are particularly sensitive to Hsp90-Is as compared to the low CD45 expressers may provide a rational basis for selection of MM patients amenable to Hsp90-I treatment.
分子伴侣 Hsp90 对于维持许多信号蛋白的活性是必需的，包括 JAK/STAT 和 PI3K 途径的成员。在临床试验中，Hsp90 抑制剂（Hsp90-Is）对多发性骨髓瘤（MM）显示出不同的活性。我们旨在确定哪些信号通路导致在一组 MM 细胞系和新获得的 MM 细胞中对 Hsp90-I 17DMAG 的敏感性存在差异。三个具有激活的 JAK/STAT3 途径的 CD45(+)细胞系对 17DMAG 敏感，并在治疗后经历明显的凋亡，而大多数依赖激活的 PI3K 途径的 CD45(-)细胞系对该药物更具抗性。在存在 IL-6 的情况下培养最耐药的细胞系 LP1 导致 CD45 和 pSTAT3 的上调，并对 17DMAG 诱导的凋亡敏感，主要是在诱导的 CD45(+)细胞亚群中。与低 CD45 表达者相比，原发性骨髓瘤细胞中的高 CD45 表达者也表达明显更高水平的 pSTAT3。在原发性骨髓瘤细胞中，用 17DMAG 进行体外治疗导致在高 CD45 表达者为主的肿瘤样本中 caspase3 激活更强。Hsp90-Is 有效地抑制了细胞系和原代细胞中的 STAT3 活性，这表明 STAT3 失活对于 HSP90-Is 的促凋亡作用很重要。事实上，在 U266 细胞中过表达具有增加 DNA 结合活性的变体 STAT3C 可保护它们免受 17DMAG 诱导的细胞死亡。在 17DMAG 处理后，STAT3C 表达细胞中 STAT3 靶基因 Mcl-1 的 mRNA 和蛋白水平的下调明显减弱，瞬时过表达 Mcl-1 可保护 U266 细胞免受 17DMAG 诱导的细胞死亡。与低 CD45 表达者相比，具有 IL-6 激活的 JAK/STAT3 途径的 CD45(+)MM 细胞对 Hsp90-Is 特别敏感的发现可能为选择适合 Hsp90-I 治疗的 MM 患者提供合理依据。
