Multiple complexes involved in tyrosine hydroxylase mRNA stability in rat adrenal medulla, after reserpine stimulation.

A 28-nucleotide sequence within the 3'-untranslated region (3'UTR) of tyrosine hydroxylase (TH) mRNA has been suggested to influence the turnover rate of the TH messenger in vitro (W. R. Paulding and M. F. Czyzyk-Krzeska, 1999, J. Biol. Chem. 274, 2532-2538). In this study, we show that treatment with reserpine, a catecholamine-depleting drug which increases the stability of TH mRNA, allows the binding of a cytosolic protein to this 28-mer site in the TH 3'UTR in the rat adrenal medulla. An ex vivo kinetic analysis shows that the resulting 54-kDa ribonucleoprotein is early induced by reserpine. However, the formation of this complex is not coupled with the upregulation of TH mRNA, indicating that this 54-kDa complex could not be the unique factor accountable for the long-term stabilization of the TH messenger. Following this result we found that several other cis-acting elements, located in single-stranded stem loops within the secondary structure of TH 3'UTR, formed multiple complexes (43, 54, and 105 kDa) with cytosolic, polysome-associated, and also nuclear proteins. Our findings demonstrate that the messenger stability does not depend solely on the formation of a unique RNA-protein complex, but involves mechanisms with higher complexity implicating the interactions between posttranscriptional, nuclear RNA export, and translational processes.