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Endocrinology, Vol 132, 1614-1620, Copyright © 1993 by Endocrine Society
ARTICLES |
F de Nadai, C Rovere, JN Bidard, J Laur, J Martinez, JC Cuber and P Kitabgi
Institut de Pharmacologie Moleculaire et Cellulaire, Universite de Antipolis, Valbonne, France.
Neurotensin (NT) and Neuromedin N (NN) are two biologically active peptides present in one copy each in the C-terminal region of a 169- residue precursor. Four basic Lys-Arg doublets occur within the precursor and represent putative processing sites. We investigated the effects of dexamethasone on the biosynthesis and the posttranslational processing of the NT/NN precursor in the rat medullary thyroid carcinoma 6-23 cell line (rMTC 6-23). Western blot analysis and RIA coupled to HPLC and arginine-directed tryptic cleavage of precursor forms were performed with antisera specific for precursor sequences adjacent to the four basic doublets. These studies revealed that rMTC 6- 23 cells synthesized the NT/NN precursor in response to dexamethasone and had the capability to process this precursor at the three Lys-Arg doublets that flank and separate NT and NN, thus yielding authentic NT, NN, and several larger products. The most N-terminal Lys-Arg doublet was not processed in this system. Dexamethasone increased in a concentration- and time-dependent manner the levels of all the NT/NN precursor-derived products. This increase did not affect the relative proportion of the different products. We also showed by Northern blot analysis that both the 1.1-kilobase and 1.5-kilobase NT/NN precursor messenger RNAs were present in the rMTC 6-23 cell line and that the time course and dose response of dexamethasone-induced messenger RNA synthesis were in good agreement with those observed for dexamethasone- induced increase in processing products. The rMTC 6-23 cell line represents a good model to elucidate the steps involved in the posttranslational processing of the NT/NN precursor.
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