Hormi-Carver Kathy, Feagins Linda A, Spechler Stuart J, Souza Rhonda F
1Departments of Medicine, Dallas Veterans Affairs Medical Center, University of Texas-Southwestern Medical School, Dallas, Texas 75216, USA.
Am J Physiol Gastrointest Liver Physiol. 2007 Jan;292(1):G18-27. doi: 10.1152/ajpgi.00237.2006. Epub 2006 Aug 24.
Retinoids such as all trans-retinoic acid (ATRA) have been used as chemopreventive agents for a number of premalignant conditions. To explore a potential role for retinoids as chemopreventive agents for Barrett's esophagus, we studied ATRA's effects on apoptosis in a nonneoplastic, telomerase-immortalized, metaplastic Barrett's cell line. We treated the Barrett's cells with ATRA in the presence and absence of inhibitors to p53 (pSRZ-siRNA-p53), p38 (SB-203580 and p38 siRNA), and the caspase cascade (z-Val-Ala-Asp-fluoromethyl ketone). We determined the effects of ATRA and the various inhibitors on apoptosis using cell morphology, terminal deoxynucleotidyltransferase-mediated dUTP nick-end labeling staining, cleaved caspase-3 immunofluorescence, and Annexin V staining. We also determined how ATRA in the presence and absence of the inhibitors affected apoptosis following low-dose UV-B irradiation. ATRA induced apoptosis and increased the expression of p53 protein in a dose-dependent fashion. The apoptotic effect of ATRA was abolished by treatment with inhibitors of both p38 and caspase, but not by p53 interfering RNA (RNAi). Inhibition of p38 also prevented expression of cleaved caspase-3, suggesting that ATRA activates p38 upstream of the caspase cascade. We found that ATRA sensitized immortalized Barrett's cells to apoptosis induced by low-dose UV-B irradiation via a similar mechanism. ATRA induces apoptosis in Barrett's epithelial cells and sensitizes them to apoptosis induced by UV-B irradiation via activation of p38 and the caspase cascade, but not through p53. This study elucidates molecular pathways whereby retinoid treatment might prevent carcinogenesis in Barrett's metaplasia and suggests a potential role for the use of safer retinoids for chemoprevention in Barrett's esophagus.
类视黄醇，如全反式维甲酸（ATRA），已被用作多种癌前病变的化学预防剂。为了探索类视黄醇作为巴雷特食管化学预防剂的潜在作用，我们研究了ATRA对一种非肿瘤性、端粒酶永生化的化生巴雷特细胞系凋亡的影响。我们在存在和不存在p53抑制剂（pSRZ-siRNA-p53）、p38抑制剂（SB-203580和p38 siRNA）以及半胱天冬酶级联反应抑制剂（z-Val-Ala-Asp-fluoromethyl ketone）的情况下，用ATRA处理巴雷特细胞。我们使用细胞形态学、末端脱氧核苷酸转移酶介导的dUTP缺口末端标记染色、裂解的半胱天冬酶-3免疫荧光和膜联蛋白V染色，确定了ATRA和各种抑制剂对凋亡的影响。我们还确定了在存在和不存在抑制剂的情况下，ATRA如何影响低剂量UV-B照射后的凋亡。ATRA以剂量依赖性方式诱导凋亡并增加p53蛋白的表达。用p38和半胱天冬酶抑制剂处理可消除ATRA的凋亡作用，但p53干扰RNA（RNAi）不能消除。抑制p38也可阻止裂解的半胱天冬酶-3的表达，表明ATRA在半胱天冬酶级联反应上游激活p38。我们发现，ATRA通过类似机制使永生化巴雷特细胞对低剂量UV-B照射诱导的凋亡敏感。ATRA通过激活p38和半胱天冬酶级联反应，但不通过p53，诱导巴雷特上皮细胞凋亡并使其对UV-B照射诱导的凋亡敏感。这项研究阐明了类视黄醇治疗可能预防巴雷特化生癌变的分子途径，并提示使用更安全的类视黄醇进行巴雷特食管化学预防的潜在作用。
