Yoon J H, Koo J S, Norford D, Guzman K, Gray T, Nettesheim P
Department of Otorhinolaryngology, Yonsei University College of Medicine, Seoul, Korea.
Am J Respir Cell Mol Biol. 1999 Apr;20(4):573-81. doi: 10.1165/ajrcmb.20.4.3127.
We previously reported (Gray, T. E., K. Guzman, C. W. Davis, L. H. Abdullah, and P. Nettesheim. 1996. Mucociliary differentiation of serially passaged normal human tracheobronchial epithelial cells. Am. J. Respir. Cell Mol. Biol. 14:104-112) that retinoic acid (RA)-deprived cultures of normal human tracheobronchial epithelial (NHTBE) cells became squamous, failed to produce mucin, and instead secreted or released large amounts of lysozyme (LZ). The purpose of the studies reported here was to elucidate the relationship between RA deficiency-induced squamous differentiation and increased LZ, and to determine what mechanisms were involved. We found that intracellular LZ began to accumulate in RA-deficient NHTBE cultures early during squamous differentiation. Between Days 10 and 18 of culture, cellular LZ levels were more than 10 times higher in RA-deficient than in RA-sufficient cultures. On Day 12, large numbers of cells began to exfoliate in RA-deficient cultures and extracellular LZ appeared at the apical surface, presumably released from the exfoliated cells. Metabolic labeling studies showed that the rate of LZ synthesis was not increased in RA-deficient cultures over that in RA-sufficient cultures; however, intracellular LZ half-life was much longer in RA-deficient cultures. We concluded that the increased accumulation of both intra- and extracellular LZ in RA-deficient cultures was due to increased LZ stability and was not the result of increased LZ synthesis. When RA-deficient cultures were treated on Day 7 with 10(-6) M RA, intracellular LZ levels did not substantially decrease until 3 d later, coinciding with a marked increase in mucin secretion. LZ messenger RNA levels were unchanged at 24 h, but were modestly increased (rather than decreased) at all subsequent time points. We concluded that RA does not directly regulate LZ, and that the excessive accumulation of LZ in RA-deprived NHTBE cells is a consequence of vitamin A deficiency-induced abnormal differentiation.
我们先前报道过（格雷，T.E.，K.古兹曼，C.W.戴维斯，L.H.阿卜杜拉，以及P.内特海姆。1996年。连续传代的正常人气管支气管上皮细胞的黏液纤毛分化。《美国呼吸细胞与分子生物学杂志》14:104 - 112），缺乏视黄酸（RA）培养的正常人气管支气管上皮（NHTBE）细胞会发生鳞状化生，无法产生黏蛋白，而是分泌或释放大量溶菌酶（LZ）。本文报道的研究目的是阐明RA缺乏诱导的鳞状化生与LZ增加之间的关系，并确定涉及哪些机制。我们发现，在鳞状化生早期，细胞内LZ就开始在缺乏RA的NHTBE培养物中积累。在培养的第10天至18天之间，缺乏RA的培养物中细胞LZ水平比补充RA的培养物高10倍以上。在第12天，大量细胞开始从缺乏RA的培养物中脱落，细胞外LZ出现在顶端表面，推测是从脱落细胞中释放出来的。代谢标记研究表明，缺乏RA的培养物中LZ的合成速率并不比补充RA的培养物高；然而，缺乏RA的培养物中细胞内LZ的半衰期要长得多。我们得出结论，缺乏RA的培养物中细胞内和细胞外LZ积累的增加是由于LZ稳定性增加，而不是LZ合成增加的结果。当在第7天用10⁻⁶ M RA处理缺乏RA的培养物时，细胞内LZ水平直到3天后才大幅下降，这与黏蛋白分泌的显著增加同时发生。LZ信使核糖核酸水平在24小时时未改变，但在所有后续时间点均适度增加（而非降低）。我们得出结论，RA并不直接调节LZ，并且在缺乏RA的NHTBE细胞中LZ的过度积累是维生素A缺乏诱导的异常分化的结果。
