Haugstad Kristin E, Hadjialirezaei Soosan, Stokke Bjørn T, Brewer C Fred, Gerken Thomas A, Burchell Joy, Picco Gianfranco, Sletmoen Marit
Department of Physics, Biophysics and Medical Technology, The Norwegian University of Science and Technology (NTNU), NO-7491 Trondheim, Norway.
Departments of Molecular Pharmacology, and Microbiology and Immunology, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
Glycobiology. 2016 Dec;26(12):1338-1350. doi: 10.1093/glycob/cww065. Epub 2016 Jun 9.
The molecular mechanism(s) underlying the enhanced self-interactions of mucins possessing the Tn (GalNAcα1-Ser/Thr) or STn (NeuNAcα2-6GalNAcα1-Ser/Thr) cancer markers were investigated using optical tweezers (OT). The mucins examined included modified porcine submaxillary mucin containing the Tn epitope (Tn-PSM), ovine submaxillary mucin with the STn epitope (STn-OSM), and recombinant MUC1 analogs with either the Tn and STn epitope. OT experiments in which the mucins were immobilized onto polystyrene beads revealed identical self-interaction characteristics for all mucins. Identical binding strength and energy landscape characteristics were also observed for synthetic polymers displaying multiple GalNAc decorations. Polystyrene beads without immobilized mucins showed no self-interactions and also no interactions with mucin-decorated polystyrene beads. Taken together, the experimental data suggest that in these molecules, the GalNAc residue mediates interactions independent of the anchoring polymer backbone. Furthermore, GalNAc-GalNAc interactions appear to be responsible for self-interactions of mucins decorated with the STn epitope. Hence, Tn-MUC1 and STn-MUC1 undergo self-interactions mediated by the GalNAc residue in both epitopes, suggesting a possible molecular role in cancer. MUC1 possessing the T (Galβ1-3GalNAcα1-Ser/Thr) or ST antigen (NeuNAcα2-3Galβ1-3GalNAcα1-Ser/Thr) failed to show self-interactions. However, in the case of ST-MUC1, self-interactions were observed after subsequent treatment with neuraminidase and β-galactosidase. This enzymatic treatment is expected to introduce Tn-epitopes and these observations thus further strengthen the conclusion that the observed interactions are mediated by the GalNAc groups.
利用光镊（OT）研究了具有Tn（GalNAcα1 - Ser/Thr）或STn（NeuNAcα2 - 6GalNAcα1 - Ser/Thr）癌症标志物的黏蛋白增强自身相互作用的分子机制。所检测的黏蛋白包括含有Tn表位的修饰猪下颌黏蛋白（Tn - PSM）、带有STn表位的羊下颌黏蛋白（STn - OSM）以及具有Tn和STn表位的重组MUC1类似物。将黏蛋白固定在聚苯乙烯珠上的OT实验表明，所有黏蛋白具有相同的自身相互作用特征。对于显示多个GalNAc修饰的合成聚合物，也观察到了相同的结合强度和能量景观特征。未固定黏蛋白的聚苯乙烯珠既没有自身相互作用，也没有与黏蛋白修饰的聚苯乙烯珠相互作用。综上所述，实验数据表明，在这些分子中，GalNAc残基介导的相互作用独立于锚定聚合物主链。此外，GalNAc - GalNAc相互作用似乎是带有STn表位的黏蛋白自身相互作用的原因。因此，Tn - MUC1和STn - MUC1在两个表位中都经历由GalNAc残基介导的自身相互作用，提示其在癌症中可能具有分子作用。具有T（Galβ1 - 3GalNAcα1 - Ser/Thr）或ST抗原（NeuNAcα2 - 3Galβ1 - 3GalNAcα1 - Ser/Thr）的MUC1未显示自身相互作用。然而，对于ST - MUC1，在用神经氨酸酶和β - 半乳糖苷酶进行后续处理后观察到了自身相互作用。这种酶处理预期会引入Tn表位，因此这些观察结果进一步强化了所观察到的相互作用是由GalNAc基团介导的这一结论。
