Dystroglycan is present in rat thyroid and rat thyroid cells and responds to thyrotropin

Dystroglycan is a high affinity laminin-binding glycoprotein originally des cribed as a member of the dystrophin-associated glycoprotein complex in mus cle. We have demonstrated the presence of dystroglycan in the thyroid using immunocytochemistry, immunoblots, ligand binding assays, and relative quan titative RT-PCR. In intact rat thyroid glands, antibodies against the alpha (extracellular, laminin-binding subunit) and beta (cytoplasmic/membrane bo und) portions of the dystroglycan protein reacted at basolateral membranes where they colocalized with laminin. Western-blotted protein from the Fisch er rat thyroid cell line FRTL-5 reacted with both the alpha- and beta -dyst roglycan antibodies. The alpha -dystroglycan-reactive band colocalized with laminin-binding activity, and the protein and binding activity were decrea sed by TSH. In contrast, in the culture medium of these cells, alpha -dystr oglycan was increased by TSH. The beta -dystroglycan antibody recognized th e full-length 43-kDa band and an approximately 30-kDa truncated form. The t runcated form was reduced in cells cultured with TSH, whereas the full-leng th form was not significantly diminished by TSH. Immunofluorescence of FRTL -5 cells in the absence of TSH showed a colocalization of dystroglycan and laminin. This was disrupted by the addition of TSH and was correlated to mo rphologicaI changes. PCR amplification of complementary DNA with primer pai ns from alpha- and beta -dystroglycan produced appropriately sized bands, w hose sequence had identical protein-coding sequences and more than 96% nucl eotide homology to mouse dystroglycan sequences. Relative quantitative RT-P CR of beta -dystroglycan messenger RNA showed reduced expression in cells c ultured with TSH. We conclude that dystroglycan is present in rat thyroid a nd in FRTL5 rat thyroid eels and that TSH reduces its expression.