Schwartz E, Feinberg E, Lebwohl M, Mariani T J, Boyd C D
Department of Dermatology, Mount Sinai School of Medicine, New York, New York 10029, USA.
J Invest Dermatol. 1995 Jul;105(1):65-9. doi: 10.1111/1523-1747.ep12312576.
Chronically sun-damaged human skin is characterized by dermal connective tissue damage that includes the massive accumulation of abnormal elastic fibers. The content of elastin, the major protein component of elastic fibers, is increased two- to sixfold in sun-damaged skin. The aim of this study was to determine the mechanism responsible for the increase in elastin levels after ultraviolet (UV) irradiation. Confluent cultures of normal dermal fibroblasts were irradiated with 4.5 mJ/cm2 of UVB; sham-treated cells served as the control group. The accumulation of tropoelastin was determined at 5 d after treatment by measuring the incorporation of 14C-proline into radiolabeled tropoelastin isolated from cell layers and media. UV irradiation increased radiolabeled tropoelastin accumulation approximately twofold without affecting DNA content, the total amount of radiolabeled protein, or tropoelastin secretion. Moreover, the steady-state levels of tropoelastin mRNA, as determined by slot blot hybridizations, were unaffected by UV treatment. However, the translation of tropoelastin mRNA was increased when total RNA from irradiated cells was used in cell-free translation experiments. These results suggest that altered translational efficiency may account for the increase in tropoelastin accumulation after UV irradiation. In support of this hypothesis, nucleotide sequences were derived from tropoelastin mRNA isolated from UV-irradiated and nonirradiated dermal fibroblasts. Almost a 12% substitution rate was observed in nucleotide sequences derived from the 3' untranslated region of tropoelastin mRNA from the UV-treated cells. In contrast, a coding domain of tropoelastin did not contain base-substitution mutations. These multiple base substitutions in a noncoding domain of tropoelastin mRNA may be responsible for the post-transcriptional increase in tropoelastin accumulation after UV irradiation.
长期受阳光损伤的人类皮肤的特征是真皮结缔组织损伤，其中包括异常弹性纤维的大量积累。弹性蛋白是弹性纤维的主要蛋白质成分，在受阳光损伤的皮肤中，其含量增加了两到六倍。本研究的目的是确定紫外线（UV）照射后弹性蛋白水平升高的机制。用4.5 mJ/cm2的UVB照射正常真皮成纤维细胞的汇合培养物；假处理的细胞作为对照组。在处理后5天，通过测量从细胞层和培养基中分离的放射性标记原弹性蛋白中14C-脯氨酸的掺入量来确定原弹性蛋白的积累。紫外线照射使放射性标记的原弹性蛋白积累增加了约两倍，而不影响DNA含量、放射性标记蛋白质的总量或原弹性蛋白的分泌。此外，通过狭缝印迹杂交测定的原弹性蛋白mRNA的稳态水平不受紫外线处理的影响。然而，当将照射细胞的总RNA用于无细胞翻译实验时，原弹性蛋白mRNA的翻译增加。这些结果表明，翻译效率的改变可能是紫外线照射后原弹性蛋白积累增加的原因。为支持这一假设，从紫外线照射和未照射的真皮成纤维细胞中分离出原弹性蛋白mRNA，并推导其核苷酸序列。在来自紫外线处理细胞的原弹性蛋白mRNA的3'非翻译区的核苷酸序列中观察到近12%的替换率。相比之下，原弹性蛋白的编码区不包含碱基替换突变。原弹性蛋白mRNA非编码区的这些多个碱基替换可能是紫外线照射后原弹性蛋白积累转录后增加的原因。
