Ai Guoqiang, Dachineni Rakesh, Muley Pratik, Tummala Hemachand, Bhat G Jayarama
Department of Pharmaceutical Sciences, South Dakota State University College of Pharmacy, Avera Health and Sciences Center, Brookings, SD, 57007, USA.
Tumour Biol. 2016 Feb;37(2):1727-38. doi: 10.1007/s13277-015-3959-0. Epub 2015 Aug 28.
Epidemiological studies have demonstrated a significant correlation between regular aspirin use and reduced colon cancer incidence and mortality; however, the pathways by which it exerts its anti-cancer effects are still not fully explored. We hypothesized that aspirin's anti-cancer effect may occur through downregulation of c-Myc gene expression. Here, we demonstrate that aspirin and its primary metabolite, salicylic acid, decrease the c-Myc protein levels in human HCT-116 colon and in few other cancer cell lines. In total cell lysates, both drugs decreased the levels of c-Myc in a concentration-dependent fashion. Greater inhibition was observed in the nucleus than the cytoplasm, and immunofluorescence studies confirmed these observations. Pretreatment of cells with lactacystin, a proteasome inhibitor, partially prevented the downregulatory effect of both aspirin and salicylic acid, suggesting that 26S proteasomal pathway is involved. Both drugs failed to decrease exogenously expressed DDK-tagged c-Myc protein levels; however, under the same conditions, the endogenous c-Myc protein levels were downregulated. Northern blot analysis showed that both drugs caused a decrease in c-Myc mRNA levels in a concentration-dependent fashion. High-performance liquid chromatography (HPLC) analysis showed that aspirin taken up by cells was rapidly metabolized to salicylic acid, suggesting that aspirin's inhibitory effect on c-Myc may occur through formation of salicylic acid. Our result suggests that salicylic acid regulates c-Myc level at both transcriptional and post-transcription levels. Inhibition of c-Myc may represent an important pathway by which aspirin exerts its anti-cancer effect and decrease the occurrence of cancer in epithelial tissues.
流行病学研究表明，经常使用阿司匹林与降低结肠癌的发病率和死亡率之间存在显著相关性；然而，其发挥抗癌作用的途径仍未得到充分探索。我们推测阿司匹林的抗癌作用可能是通过下调c-Myc基因表达来实现的。在此，我们证明阿司匹林及其主要代谢产物水杨酸可降低人HCT-116结肠癌细胞和其他几种癌细胞系中的c-Myc蛋白水平。在全细胞裂解物中，两种药物均以浓度依赖的方式降低c-Myc的水平。在细胞核中观察到的抑制作用比细胞质中更强，免疫荧光研究证实了这些观察结果。用蛋白酶体抑制剂乳胞素对细胞进行预处理，部分阻止了阿司匹林和水杨酸的下调作用，表明26S蛋白酶体途径参与其中。两种药物均未能降低外源表达的DDK标签的c-Myc蛋白水平；然而，在相同条件下，内源性c-Myc蛋白水平却被下调。Northern印迹分析表明，两种药物均以浓度依赖的方式导致c-Myc mRNA水平降低。高效液相色谱（HPLC）分析表明，细胞摄取的阿司匹林迅速代谢为水杨酸，这表明阿司匹林对c-Myc的抑制作用可能是通过水杨酸的形成来实现的。我们的结果表明，水杨酸在转录和转录后水平上调节c-Myc水平。抑制c-Myc可能是阿司匹林发挥抗癌作用并降低上皮组织癌症发生率的重要途径。
