Department Biology and Biotechnology, Sapienza University, Rome, Italy.
Molecular and Computational Biology Department, University of Southern California, Los Angeles, CA, USA.
J Exp Clin Cancer Res. 2022 Sep 13;41(1):273. doi: 10.1186/s13046-022-02480-5.
Lamins, key nuclear lamina components, have been proposed as candidate risk biomarkers in different types of cancer but their accuracy is still debated. AKTIP is a telomeric protein with the property of being enriched at the nuclear lamina. AKTIP has similarity with the tumor susceptibility gene TSG101. AKTIP deficiency generates genome instability and, in p53 mice, the reduction of the mouse counterpart of AKTIP induces the exacerbation of lymphomas. Here, we asked whether the distribution of AKTIP is altered in cancer cells and whether this is associated with alterations of lamins.
We performed super-resolution imaging, quantification of lamin expression and nuclear morphology on HeLa, MCF7, and A549 tumor cells, and on non-transformed fibroblasts from healthy donor and HGPS (LMNA c.1824C > T p.Gly608Gly) and EDMD2 (LMNA c.775 T > G) patients. As proof of principle model combining a defined lamin alteration with a tumor cell setting, we produced HeLa cells exogenously expressing the HGPS lamin mutant progerin that alters nuclear morphology.
In HeLa cells, AKTIP locates at less than 0.5 µm from the nuclear rim and co-localizes with lamin A/C. As compared to HeLa, there is a reduced co-localization of AKTIP with lamin A/C in both MCF7 and A549. Additionally, MCF7 display lower amounts of AKTIP at the rim. The analyses in non-transformed fibroblasts show that AKTIP mislocalizes in HGPS cells but not in EDMD2. The integrated analysis of lamin expression, nuclear morphology, and AKTIP topology shows that positioning of AKTIP is influenced not only by lamin expression, but also by nuclear morphology. This conclusion is validated by progerin-expressing HeLa cells in which nuclei are morphologically altered and AKTIP is mislocalized.
Our data show that the combined alteration of lamin and nuclear morphology influences the localization of the tumor-associated factor AKTIP. The results also point to the fact that lamin alterations per se are not predictive of AKTIP mislocalization, in both non-transformed and tumor cells. In more general terms, this study supports the thesis that a combined analytical approach should be preferred to predict lamin-associated changes in tumor cells. This paves the way of next translational evaluation to validate the use of this combined analytical approach as risk biomarker.
核层蛋白是核层主要的组成成分，被认为是多种癌症的候选风险生物标志物，但它们的准确性仍存在争议。AKTIP 是端粒蛋白，具有在核层富集的特性。AKTIP 与肿瘤易感性基因 TSG101 具有相似性。AKTIP 缺失会导致基因组不稳定，在 p53 小鼠中，减少 AKTIP 的小鼠对应物会加剧淋巴瘤的发生。在这里，我们想知道 AKTIP 在癌细胞中的分布是否发生了改变，以及这种改变是否与核层蛋白的改变有关。
我们对 HeLa、MCF7 和 A549 肿瘤细胞以及来自健康供体和 HGPS（LMNA c.1824C>T p.Gly608Gly）和 EDMD2（LMNA c.775T>G）患者的非转化成纤维细胞进行了超分辨率成像、核层蛋白表达和核形态学的定量分析。作为一个将特定核层改变与肿瘤细胞环境相结合的原理模型，我们产生了外源性表达 HGPS 核层突变蛋白 progerin 的 HeLa 细胞，该蛋白改变了核形态。
在 HeLa 细胞中，AKTIP 位于距核边缘不到 0.5µm 的位置，与核层蛋白 A/C 共定位。与 HeLa 细胞相比，MCF7 和 A549 细胞中 AKTIP 与核层蛋白 A/C 的共定位减少。此外，MCF7 细胞边缘的 AKTIP 含量较低。非转化成纤维细胞的分析表明，AKTIP 在 HGPS 细胞中发生了定位错误，但在 EDMD2 细胞中没有。核层蛋白表达、核形态和 AKTIP 拓扑结构的综合分析表明，AKTIP 的定位不仅受核层蛋白表达的影响，还受核形态的影响。这一结论在表达 progerin 的 HeLa 细胞中得到了验证，在这些细胞中，核形态发生了改变，AKTIP 发生了定位错误。
我们的数据表明，核层和核形态的联合改变会影响肿瘤相关因子 AKTIP 的定位。研究结果还表明，非转化和肿瘤细胞中，核层蛋白的改变本身并不能预测 AKTIP 的定位错误。更一般地说，本研究支持这样一种观点，即应该采用综合分析方法来预测肿瘤细胞中与核层相关的变化。这为下一步的转化评估铺平了道路，以验证这种综合分析方法作为风险生物标志物的使用。
