Martín-Belmonte F, Kremer L, Albar J P, Marazuela M, Alonso M A
Centro de Biología Molecular Severo Ochoa, Universidad Autónoma de Madrid and Consejo Superior de Investigaciones Científicas, Cantoblanco, Spain.
Endocrinology. 1998 Apr;139(4):2077-84. doi: 10.1210/endo.139.4.5875.
The MAL proteolipid, an integral membrane protein expressed in T lymphocytes, polarized epithelial MDCK cells, and myelin-forming cells, has been identified as a component of internal glycolipid-enriched membrane (GEM) microdomains. On the basis of its ability to induce vesicle formation by ectopic expression, MAL has been recently proposed as a component of the machinery for GEM vesiculation. Taking into account the proposed role of GEMs in polarized transport, we have investigated the expression of the MAL gene in thyroid cells. Interestingly, MAL messenger RNA species were detected in the human thyroid, whereas they were undetectable in other endocrine glands tested. Moreover, epithelial FRT cells, a polarized rat cell line of thyroid origin, also expressed MAL transcripts. Immunohistochemical analysis of thyroid follicles, with a newly developed anti-MAL monoclonal antibody, indicates that MAL distribution is restricted to the apical zone of thyroid epithelial cells. Biochemical analyses, using FRT cells, indicate exclusive residence of MAL in GEM microdomains, and these analyses allowed the identification of MAL as a major protein component of the GEM fraction in this cell line. Our results are consistent with a role for MAL as a component of GEM microdomains in thyroid epithelial cells.
MAL蛋白脂质是一种整合膜蛋白，在T淋巴细胞、极化上皮MDCK细胞和形成髓鞘的细胞中表达，已被鉴定为富含糖脂的内膜（GEM）微区的一个组成部分。基于其通过异位表达诱导囊泡形成的能力，MAL最近被认为是GEM囊泡化机制的一个组成部分。考虑到GEM在极化运输中的假定作用，我们研究了MAL基因在甲状腺细胞中的表达。有趣的是，在人甲状腺中检测到了MAL信使RNA，而在其他受试内分泌腺中未检测到。此外，上皮FRT细胞是一种源自甲状腺的极化大鼠细胞系，也表达MAL转录本。用新开发的抗MAL单克隆抗体对甲状腺滤泡进行免疫组织化学分析表明，MAL的分布仅限于甲状腺上皮细胞的顶端区域。使用FRT细胞进行的生化分析表明，MAL仅存在于GEM微区，这些分析使MAL被鉴定为该细胞系中GEM组分的主要蛋白质成分。我们的结果与MAL作为甲状腺上皮细胞中GEM微区组成部分的作用一致。
