The C-terminal domain of the adenomatous polyposis coli (Apc) protein is involved in thyroid morphogenesis and function

Adenomatous polyposis coli (APC) is a multifunctional protein as well as a tumor suppressor. To determine the functions of the C-terminal domain of Apc, we have investigated Apc1638T/1638Tmice, which express a truncated Apc that lacks the C-terminal domain. Apc1638T/1638Tmice are tumor free and exhibit growth retardation. In the present study, we analyzed the morphology and functions of the thyroid gland in Apc1638T/1638Tmice. There was no significant difference in the basal concentration of serum thyroid hormones between Apc1638T/1638Tand Apc+/+mice. Thyroid follicle size was significantly larger in Apc1638T/1638Tmice than in Apc+/+mice. The extent of serum T4 elevation following exogenous thyroid-stimulating hormone (TSH) injection was lower in Apc1638T/1638Tmice than in Apc+/+mice. TSH also induced a greater reduction in thyroid follicle size in Apc1638T/1638Tmice than in Apc+/+mice. Analyses using immunohistochemistry and electron microscopy indicated that follicular epithelial cells in Apc1638T/1638Tmice had an enlarged rough endoplasmic reticulum of irregular shape. These results suggest that the C-terminal domain of Apc is involved in thyroid morphology and function.

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