Nabeyrat E, Corroyer S, Epaud R, Besnard V, Cazals V, Clement A
Departement de Pneumologie Pediatrique, Institut National de la Santé et de la Recherche Médicale Unité 515, Hôpital Trousseau Assistance Publique-Hôpitaux de Paris, Université Paris VI, 75012 Paris, France.
Am J Physiol Lung Cell Mol Physiol. 2000 Jan;278(1):L42-50. doi: 10.1152/ajplung.2000.278.1.L42.
Retinoids, including retinol and retinoic acid (RA) derivatives, have been shown to be involved in the processes of lung development as well as of lung repair after injury. Recently, we have provided evidence that RA could stimulate proliferation of lung alveolar type 2 epithelial cells (E. Nabeyrat, V. Besnard, S. Corroyer, V. Cazals, and A. Clement. Am. J. Physiol. Lung Cell. Mol. Physiol. 275: L71-L79, 1998). To gain some insight into the mechanisms involved in the mitogenic action of RA, we focused in the present study on the effects of RA on the expression of G(1) phase cyclins and their cell cycle-dependent kinases (Cdks). Experiments were performed with serum-deprived cells cultured in the absence and presence of RA. The results showed no effects of RA on the expression of either cyclins or Cdks. In contrast, RA treatment was found to prevent the decrease in cyclin E-Cdk2 activity observed when cells were growth arrested by serum deprivation. The observation that changes in cyclin E-Cdk2 activity were not associated with modifications in the amount of complexes formed led to the suggestion that the Cdk inhibitory protein (CKI) was involved. Study of the CKI p21(CIP1) revealed marked differences in its expression in the absence and presence of RA, with a dramatic downregulation observed in RA-treated cells. Interestingly, immunoprecipitation experiments provided evidence that the decreased levels of p21(CIP1) were associated with a reduced interaction of this CKI with cyclin E-Cdk2 complexes. These data together with previous results obtained in various situations of type 2 cell growth arrest emphasize the role of p21(CIP1) in the control of lung alveolar epithelial cell proliferation.
维甲酸类物质，包括视黄醇和维甲酸（RA）衍生物，已被证明参与肺发育过程以及损伤后的肺修复过程。最近，我们已提供证据表明RA可刺激肺泡Ⅱ型上皮细胞增殖（E. 纳贝拉特、V. 贝纳尔、S. 科罗耶、V. 卡扎尔和A. 克莱门特。《美国生理学杂志：肺细胞与分子生理学》275: L71 - L79, 1998）。为深入了解RA促有丝分裂作用的机制，在本研究中我们聚焦于RA对G1期细胞周期蛋白及其细胞周期依赖性激酶（Cdks）表达的影响。实验在无血清培养且添加或不添加RA的细胞中进行。结果表明RA对细胞周期蛋白或Cdks的表达均无影响。相反地，发现RA处理可防止在血清剥夺使细胞生长停滞时所观察到的细胞周期蛋白E - Cdk₂活性降低。细胞周期蛋白E - Cdk₂活性的变化与所形成复合物数量的改变无关这一观察结果提示细胞周期蛋白依赖性激酶抑制蛋白（CKI）参与其中。对CKI p21(CIP1)的研究显示其在有无RA时的表达存在显著差异，在经RA处理的细胞中观察到明显下调。有趣的是，免疫沉淀实验提供证据表明p21(CIP1)水平的降低与该CKI与细胞周期蛋白E - Cdk₂复合物的相互作用减少有关。这些数据连同先前在各种Ⅱ型细胞生长停滞情况下获得的结果强调了p21(CIP1)在控制肺泡上皮细胞增殖中的作用。
