NPC1L1 and SR-BI are involved in intestinal cholesterol absorption from small-size lipid donors.

In the human intestinal content after a meal, cholesterol is dispersed in a complex mixture of emulsified droplets, vesicles, mixed micelles and precipitated material. The aim of this study was to determine the contribution of the main intestinal cholesterol transporters (NPC1L1, SR-BI) to the absorption processes, using different cholesterol-solubilizing donors. Cholesterol donors prepared with different taurocholate concentrations were added to an apical medium of differentiated TC7/Caco-2 cells.

A plasminogen-like protease in thyroid rough microsomes degrades thyroperoxidase and thyroglobulin.

Proteasome activity takes place in the cytosolic compartment and acts to degrade several proteins translated and unfolded. In transfected CHO cells expressing thyroid peroxidase (TPO), just-translated TPO undergoes proteasome activity, and then a second proteolytic system degrades more mature forms of TPO. A plasminogen-like (Pl-like) protease is found in microsomal liver membranes and in the thyroid.

The plasminogen-like molecule apically secreted by epithelial thyroid cells is sulfated.

Plasminogen (Pl), a circulating protease synthesized in the liver, is also present in several tissues. In the thyroid gland a Pl-like protease was found in the apical lumen where it is involved, through its proteolytic activity, in luminal degradation of thyroglobulin (Tg). Here, we showed for the first time that the Pl-like protease apically secreted by epithelial thyroid cells is sulfated, both on tyrosine residue(s) and on oligosaccharide side chains.

A plasminogen-like protein, present in the apical extracellular environment of thyroid epithelial cells, degrades thyroglobulin in vitro.

The prothyroid hormone, thyroglobulin (Tg), is stored at high concentrations in the thyroid follicular lumen as a soluble 19S homo-dimer and as heavier soluble (27S and 37S) and insoluble (Tgm) forms. Follicular degradation of Tg may contribute to maintaining Tg concentrations compatible with follicle integrity. Here, we report on the presence of a plasminogen-like protein in the follicular lumen of normal human thyroids and its synthesis and apical secretion by cultured epithelial thyroid cells.

Association of the thyrotropin receptor with calnexin, calreticulin and BiP. Efects on the maturation of the receptor.

The thyrotropin receptor (TSHR) is a member of the G protein-coupled receptor superfamily. It has by now been clearly established that the maturation of the glycoproteins synthesized in the endoplasmic reticulum involves interactions with molecular chaperones, which promote the folding and assembly of the glycoproteins. In this study, we investigated whether calnexin (CNX), calreticulin (CRT) and BiP, three of the main molecular chaperones present in the endoplasmic reticulum, interact with the TSHR and what effects these interactions might have on the folding of the receptor.