ABSTRACT

Lung cancer is a leading cause of cancer-associated death in all over the globe. This study was undertaken to determine the expression and interaction of membrane-bound receptors CD74 and CD44 in human lung adenocarcinoma cells and their associated signaling was also attempted. Levels of CD74 and CD44 were studied in human lung adenocarcinoma-evolved cells A549 and H460. CD74-mediated downstream signaling was studied by the nuclear-transcription-factor NF-κB and prostaglandin E₂ (PGE₂) production. Flow-cytometric analysis showed that both CD74 and CD44 were perfectly expressed in A549 cells. Importantly, Western immunoblotting showed that A549 cells expressed only two isoforms of CD74 at 33 and 35 kDa but isoform at 41 kDa was absent. These results were verified in H460 cells. Confocal microscopy showed CD74 and CD44 was colocalized but heterotypic interaction between them was missing in both A549 and H460 cells. Activation of NF-κB and production of PGE₂ in human lung cancer cells were comparable with other cancer cells. In conclusion, this is the first study that shows A549 and H460 cells expressed two distinctive isoforms of CD74 but isoform at 41 kDa was absent. Due to the absence of this isoform, the direct physical interaction between them CD74 and CD44 was lacking. Furthermore, the data also demonstrated that lacking of direct physical interaction between CD74 and CD44 had no effect on NF-κB activation and PGE₂ production indicating that CD74-mediated downstream signaling occurs either through coreceptors or indirect interaction with CD44 in human lung cancer cells.

Abbreviation: CD: cluster of differentiation; SCLC: small cell lung cancer; NSCLC: nonsmall cell lung cancer; SCC: squamous cell carcinoma; ADC: adenocarcinoma; LCC: large cell carcinoma

摘要

肺癌是全球癌症相关死亡的主要原因。本研究旨在确定人肺腺癌细胞中膜结合受体 CD74 和 CD44 的表达和相互作用，并尝试了它们相关的信号传导。在人肺腺癌细胞 A549 和 H460 中研究了 CD74 和 CD44 的水平。CD74 介导的下游信号通过核转录因子 NF-κB 和前列腺素 E ₂ (PGE ₂） 生产。流式细胞仪分析表明，CD74 和 CD44 在 A549 细胞中均能完美表达。重要的是，Western 免疫印迹显示 A549 细胞仅在 33 和 35 kDa 表达 CD74 的两种同种型，但不存在 41kDa 的同种型。这些结果在 H460 细胞中得到验证。共聚焦显微镜显示 CD74 和 CD44 是共定位的，但它们之间的异型相互作用在 A549 和 H460 细胞中均缺失。NF-κB 的激活和 PGE _2的产生在人肺癌细胞中的含量与其他癌细胞相当。总之，这是第一项显示 A549 和 H460 细胞表达 CD74 的两种独特同种型但不存在 41kDa 同种型的研究。由于缺乏这种同种型，它们之间的直接物理相互作用 CD74 和 CD44 缺乏。此外，数据还表明，CD74 和 CD44 之间缺乏直接的物理相互作用对 NF-κB 活化和 PGE ₂产生没有影响，表明 CD74 介导的下游信号通过辅助受体或与人肺癌细胞中的 CD44 间接相互作用发生。

缩写：CD：分化簇；SCLC：小细胞肺癌；NSCLC：非小细胞肺癌；SCC：鳞状细胞癌；ADC：腺癌；LCC：大细胞癌