Thyroid functions of mouse cathepsins B, K, and L
Bianca Friedrichs, Carmen Tepel, Thomas Reinheckel, Jan Deussing, Kurt von Figura, Volker Herzog, Christoph Peters, Paul Saftig, Klaudia Brix
Bianca Friedrichs, Carmen Tepel, Thomas Reinheckel, Jan Deussing, Kurt von Figura, Volker Herzog, Christoph Peters, Paul Saftig, Klaudia Brix
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Thyroid functions of mouse cathepsins B, K, and L

Abstract

Thyroid function depends on processing of the prohormone thyroglobulin by sequential proteolytic events. From in vitro analysis it is known that cysteine proteinases mediate proteolytic processing of thyroglobulin. Here, we have analyzed mice with deficiencies in cathepsins B, K, L, B and K, or K and L in order to investigate which of the cysteine proteinases is most important for proteolytic processing of thyroglobulin in vivo. Immunolabeling demonstrated a rearrangement of the endocytic system and a redistribution of extracellularly located enzymes in thyroids of cathepsin-deficient mice. Cathepsin L was upregulated in thyroids of cathepsin K–/– or B–/–/K–/– mice, suggesting a compensation of cathepsin L for cathepsin K deficiency. Impaired proteolysis resulted in the persistence of thyroglobulin in the thyroids of mice with deficiencies in cathepsin B or L. The typical multilayered appearance of extracellularly stored thyroglobulin was retained in cathepsin K–/– mice only. These results suggest that cathepsins B and L are involved in the solubilization of thyroglobulin from its covalently cross-linked storage form. Cathepsin K–/–/L–/– mice had significantly reduced levels of free thyroxine, indicating that utilization of luminal thyroglobulin for thyroxine liberation is mediated by a combinatory action of cathepsins K and L.

Authors

Bianca Friedrichs, Carmen Tepel, Thomas Reinheckel, Jan Deussing, Kurt von Figura, Volker Herzog, Christoph Peters, Paul Saftig, Klaudia Brix

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Tg persistence in thyroids of mice with deficiencies in cathepsin B or L...
Tg persistence in thyroids of mice with deficiencies in cathepsin B or L. Lysates of thyroids from mice of the indicated genotypes were normalized to equal amounts of protein, separated on 10% SDS gels, and transferred to nitrocellulose for subsequent incubation of the blots with antibodies against Tg. (a) A representative immunoblot. (b) The uppermost portion of another immunoblot demonstrates the expression of dimeric (thick line) and monomeric Tg (thin line) in WT and all cathepsin-deficient thyroids, as well as the appearance of a high–molecular weight Tg fragment (broken line), which was observed in the lysates of cathepsin K–/–/L–/– thyroids only. Molecular mass markers are indicated in the left margin. (c) Densitometric profiles of the indicated bands representing intact Tg and several of its degradation fragments. (d) Three different immunoblots with two lanes per genotype were evaluated densitometrically. Mean values ± SD of the densities of the lanes are given. Note that the amounts of immunolabeled Tg were upregulated about five- to sixfold in thyroids of cathepsin B– or L–deficient mice, whereas cathepsin K–/– thyroids contained only about twofold the amounts of Tg present in WTs (d).