Tesfaigzi J, Th'ng J, Hotchkiss J A, Harkema J R, Wright P S
Inhalation Toxicology Research Institute, Albuquerque, New Mexico 87185, USA.
Am J Respir Cell Mol Biol. 1996 May;14(5):478-86. doi: 10.1165/ajrcmb.14.5.8624253.
Small proline-rich proteins, believed to be precursor proteins for the crosslinked envelope formation in cells undergoing squamous differentiation, are encoded by the SPRR genes. To further investigate the role of these proteins, the time course of increased synthesis of SPRR1 mRNA in nasal epithelia of rats exposed to cigarette smoke was determined, and the deduced amino acid sequence of the rat SPRR1 was compared with those of other species. Using the pig homologue (20K) antisense cRNA probe, high levels of SPRR1 transcript were detected by in situ hybridization in squamous epithelia that line the nasal vestibule and hard palate of the rat. Basal cells of both the vestibule and palate contained low levels of the transcript, and increasing amounts were detected in the squamous layers. In rats exposed to 250 mg/m3 (total particulate matter) cigarette smoke 6 h/day for 5 days, the number of small mucous cells increased in the respiratory epithelium of the nasal septum in the early stages of squamous differentiation, but were gradually replaced by squamous metaplastic cells. During this transition, hybridization of the 20K antisense cRNA probe increased in the epithelial and mesenchymal cells, indicating that SPRR1 protein could have roles in cellular differentiation other than as a building block of the crosslinked envelope. Similarly, high levels of SPRR1 transcript were detected in the nasal transitional epithelium lining internal walls and maxilloturbinates that had undergone squamous metaplasia after cigarette smoke exposure. At 5 days after the withdrawal of cigarette smoke exposure, the morphology of the midseptal epithelium returned to that of a pseudostratified mucociliary epithelium and the epithelia lining the maxilloturbinates to that of a transitional epithelium. Accompanying this change in morphology of the tissues, the levels of SPRR1 transcripts significantly decreased in the epithelia. However, in the mesenchyme no significant decrease was observed during this recovery. RNA prepared from the external nose surrounding the nasal vestibule contained a transcript of about 0.9 kb that hybridized to the 20K cDNA probe on Northern blot analysis. DNA sequence analysis of the transcript confirmed the identity as that of the SPRR mRNA with its characteristic repeat encoding the oligopeptide with the general consensus -EPC*PKVP-. However, the rat homologue rSPRR1 contained more repeats of the oligopeptide compared with those of higher mammals such as the rabbit, pig, and human, suggesting a possible inverse relation between number of repeats and evolution development. This finding suggests that the number of repeats in the protein may be redundant; however, the conserved sequence of the peptide indicates that this region is essential for the function of this protein.
富含脯氨酸的小蛋白被认为是经历鳞状分化的细胞中交联包膜形成的前体蛋白，由SPRR基因编码。为了进一步研究这些蛋白的作用，测定了暴露于香烟烟雾的大鼠鼻上皮中SPRR1 mRNA合成增加的时间进程，并将大鼠SPRR1推导的氨基酸序列与其他物种的进行了比较。使用猪同源物（20K）反义cRNA探针，通过原位杂交在大鼠鼻前庭和硬腭内衬的鳞状上皮中检测到高水平的SPRR1转录本。前庭和腭的基底细胞中该转录本水平较低，而在鳞状层中检测到的量逐渐增加。在每天暴露于250 mg/m3（总颗粒物）香烟烟雾6小时、持续5天的大鼠中，在鳞状分化早期鼻中隔呼吸上皮中小黏液细胞数量增加，但逐渐被鳞状化生细胞取代。在这个转变过程中，20K反义cRNA探针在上皮细胞和间充质细胞中的杂交增加，表明SPRR1蛋白除了作为交联包膜的组成部分外，可能在细胞分化中发挥作用。同样，在暴露于香烟烟雾后发生鳞状化生的鼻内壁和上颌鼻甲内衬的鼻过渡上皮中检测到高水平的SPRR1转录本。停止香烟烟雾暴露5天后，鼻中隔中部上皮的形态恢复为假复层黏液纤毛上皮，上颌鼻甲内衬的上皮恢复为过渡上皮。伴随着组织形态的这种变化，上皮中SPRR1转录本的水平显著下降。然而，在间充质中，在这个恢复过程中未观察到显著下降。从鼻前庭周围的外鼻制备的RNA在Northern印迹分析中含有一个约0.9 kb的转录本，与20K cDNA探针杂交。该转录本的DNA序列分析证实其与SPRR mRNA一致，其特征性重复序列编码具有通用共识-EPC*PKVP-的寡肽。然而，与兔、猪和人等高等哺乳动物相比，大鼠同源物rSPRR1含有更多的寡肽重复序列，这表明重复序列的数量与进化发育之间可能存在反比关系。这一发现表明该蛋白中的重复序列数量可能是多余的；然而，该肽段的保守序列表明该区域对该蛋白的功能至关重要。
