Thyrotropin activates guanosine 5'-diphosphate/guanosine 5'-triphosphate exchange on the rate-limiting endocytic catalyst, Rab5a, in human thyrocytes in vivo and in vitro
| Autor: | Pierre J. Courtoy, Donatienne Tyteca, Charlotte Selvais, Marie-France van den Hove, Karine Croizet-Berger, Philippe de Diesbach |
|---|---|
| Rok vydání: | 2007 |
| Předmět: |
medicine.medical_specialty
Endocrinology Diabetes and Metabolism media_common.quotation_subject medicine.medical_treatment Clinical Biochemistry Endocytic cycle Thyroid Gland Guanosine Thyrotropin Biology In Vitro Techniques Endocytosis Biochemistry Guanosine Diphosphate Nucleotide exchange factor Iodine Radioisotopes chemistry.chemical_compound Endocrinology Thyroid-stimulating hormone Internal medicine medicine Guanine Nucleotide Exchange Factors Humans Internalization Cells Cultured media_common rab5 GTP-Binding Proteins Biochemistry (medical) Cell Polarity Protein Transport chemistry Thyroglobulin Guanosine Triphosphate Endocrine gland Subcellular Fractions |
| Zdroj: | The Journal of clinical endocrinology and metabolism. 92(7) |
| ISSN: | 0021-972X |
| Popis: | Context: We have previously reported that the TSH receptor/cAMP cascade enhances the coordinate expression of the rate-limiting endocytic catalysts, Rab5a and Rab7, which respectively promote thyroglobulin (Tg) internalization and transfer to lysosomes, thereby accelerating thyroid hormone secretion.Objective: We address whether TSH further controls Rab5a activity by promoting its GTP-bound state.Design: We compared Rab5a activation in seven pairs of hyperactive and corresponding quiescent thyroid tissues; TSH effect was reproduced on polarized cultures of normal human thyrocytes.Patients: We studied seven euthyroid patients bearing hyperactive autonomous adenomas; normal thyroid tissue for culture.Main Outcome Measurements: Rab5a GDP/GTP exchange factor activity [Rab5a-guanine nucleotide exchange factor (GEF)], expression of Rabex-5 (a Rab5a-GEF), and function of thyrocytes in vitro were the main outcome measures.Results: In autonomous adenomas, constitutive activation increased both total activity and sedimentability (membrane recruitment) of Rab5a-GEF, compared with perinodular tissues. Increased Rab5a-GEF activity correlated with increased expression of Rabex-5 and Rab5a, as well as with Tg store depletion. In polarized human thyrocyte monolayers, TSH did not affect total Rab5a-GEF activity after 2 h but promoted its membrane recruitment; after 4 d, TSH increased both Rab5a-GEF activity and Rabex-5 expression and recruitment onto membranes where Rabex-5 coimmunoprecipitated with Rabaptin-5 and Rab5a. Sedimentable Rab5a-GEF perfectly correlated with apical endocytosis and lysosomal transfer of 125I-Tg, and with basolateral secretion of 125I-derived hormones.Conclusion: This study provides the first clinical and experimental evidence that regulation of the activity of a rate-limiting endocytic catalyst finely tunes a tightly controlled cellular function that ultimately governs whole body metabolism. |
| Databáze: | OpenAIRE |
| Externí odkaz: |
|