Department of Laboratory Medicine and Pathology, University of Alberta, Edmonton, AB T6G 2R3, Canada.
Department of Medicine, Division of Hematology, University of Alberta, Edmonton, AB T6G 2R3, Canada.
Int J Mol Sci. 2023 Sep 20;24(18):14337. doi: 10.3390/ijms241814337.
In ALK-positive anaplastic large cell lymphoma (ALK+ALCL), a small subset of cancer stem-like (or RR) cells characterized by high Myc expression have been identified. We hypothesize that NPM-ALK contributes to their high Myc expression. While transfection of into HEK293 cells effectively increased Myc by inhibiting its proteosomal degradation (PD-Myc), this effect was dramatically attenuated when the full-length NPM1 (FL-NPM1) was downregulated using shRNA, highlighting the importance of the NPM-ALK:FL-ALK heterodimers in this context. Consistent with this concept, immunoprecipitation experiments showed that the heterodimers are abundant only in RR cells, in which the half-life of Myc is substantially longer than the bulk cells. Fbw7γ, a key player in PD-Myc, is sequestered by the heterodimers in RR cells, and this finding correlates with a Myc phosphorylation pattern indicative of ineffective PD-Myc. Using confocal microscopy and immunofluorescence staining, we found that the fusion signal between ALK and FL-NPM1, characteristic of the heterodimers, correlates with the Myc level in ALK+ALCL cells from cell lines and patient samples. To conclude, our findings have revealed a novel oncogenic function of NPM-ALK in the nucleus. Specifically, the NPM-ALK:FL-NPM1 heterodimers increase cancer stemness by blocking PD-Myc and promoting Myc accumulation in the cancer stem-like cell subset.
在间变性大细胞淋巴瘤（ALK+ALCL）中，一小部分具有高 Myc 表达特征的癌症干细胞样（或 RR）细胞已被鉴定出来。我们假设 NPM-ALK 有助于它们高 Myc 表达。虽然转染到 HEK293 细胞中可以通过抑制其蛋白酶体降解（PD-Myc）来有效增加 Myc，但当使用 shRNA 下调全长 NPM1（FL-NPM1）时，这种效应显著减弱，这突出了 NPM-ALK：FL-ALK 异二聚体在这种情况下的重要性。与这一概念一致，免疫沉淀实验表明，只有在 RR 细胞中才存在丰富的异二聚体，在 RR 细胞中 Myc 的半衰期明显长于大部分细胞。Fbw7γ 是 PD-Myc 的关键调控因子，在 RR 细胞中被异二聚体隔离，这一发现与 Myc 磷酸化模式相关，表明 PD-Myc 无效。通过共聚焦显微镜和免疫荧光染色，我们发现，ALK 和 FL-NPM1 之间的融合信号，是异二聚体的特征，与来自细胞系和患者样本的 ALK+ALCL 细胞中的 Myc 水平相关。总之，我们的发现揭示了 NPM-ALK 在核内的一种新的致癌功能。具体来说，NPM-ALK：FL-NPM1 异二聚体通过阻断 PD-Myc 并促进 Myc 在癌症干细胞样细胞亚群中的积累，增加了癌症干细胞样性。
