Expression of the MAL gene in the thyroid: the MAL proteolipid, a component of glycolipid-enriched membranes, is apically distributed in thyroid follicles.
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.
Martín-Belmonte
F
F
Centro de Biología Molecular Severo Ochoa, Universidad Autónoma de Madrid and Consejo Superior de Investigaciones Científicas, Cantoblanco, Spain.
Kremer
L
L
Albar
J P
JP
Marazuela
M
M
Alonso
M A
MA
D000595:Amino Acid Sequence; D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology; D000918:Antibody Specificity; D002460:Cell Line; D002462:Cell Membrane / Q000737:chemistry; D004847:Epithelial Cells / Q000737:chemistry; D015870:Gene Expression; D006017:Glycolipids / Q000032:analysis; D006801:Humans; D026901:Membrane Transport Proteins; D051379:Mice; D009185:Myelin Proteins; D062806:Myelin and Lymphocyte-Associated Proteolipid Proteins; D010446:Peptide Fragments / Q000276:immunology; D011510:Proteolipids / Q000032:analysis / Q000737:chemistry / Q000235:genetics*; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D016415:Sequence Alignment; D013961:Thyroid Gland / Q000737:chemistry*; D014018:Tissue Distribution
D000911:Antibodies, Monoclonal; D006017:Glycolipids; C569026:MAL protein, human; C569027:Mal protein, mouse; C569028:Mal protein, rat; D026901:Membrane Transport Proteins; D009185:Myelin Proteins; D062806:Myelin and Lymphocyte-Associated Proteolipid Proteins; D010446:Peptide Fragments; D011510:Proteolipids; D012333:RNA, Messenger