Tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamine biosynthesis, is induced by hypoxia in oxygensensitive cells of the carotid body and pheochromocytomaderived PC12 cells. TH is also regulated by the von Hippel-Lindau tumor suppressor protein (pVHL). Here, we report that induction of TH gene expression involves activation of the hypoxia-inducible transcription factors (HIFs) that interact with a specific hypoxia-responsive element (HRE) in the proximal region of the TH promoter. We also show that some of the effects of pVHL on activity of the TH promoter are mediated through HIFs. Low levels of pVHL are associated with decreased HIFa ubiquitination, increased accumulation of HIFa proteins, increased binding of HIFs to the HRE within the TH promoter, and increased activity of a TH promoterreporter construct. In contrast, high levels of pVHL repress HIF accumulation and inhibit its activity in hypoxic cells. These results indicate that HIFs may play an important role in regulation of TH gene expression in oxygen-sensitive cells and also in the development of hypercatecholaminemia in pheochromocytoma tumors.

The stability of mRNA for tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamine synthesis, is regulated by oxygen tension in the pheochromocytomaderived PC12 cell line. We previously identified a pyrimidine-rich 27-base-long protein-binding sequence in the 3-untranslated region of TH mRNA that is associated with hypoxia-inducible formation of a ribonucleoprotein complex (hypoxia-inducible protein-binding site (HIPBS)). In this study, we show that HIPBS is an mRNA stabilizing element necessary for both constitutive and hypoxia-regulated stability of TH mRNA. The mutations within this sequence that abolish protein binding markedly decrease constitutive TH mRNA stability and ablate its hypoxic regulation. A short fragment of TH mRNA that contains the wild-type HIPBS confers the increased mRNA stability to the reporter chloramphenicol acetyltransferase mRNA. However, it is not sufficient to confer hypoxic regulation. The HIPBS element binds two isoforms of a 40-kDa poly(C)-binding protein (PCBP). Hypoxia induces expression of the isoform 1, PCBP 1 , but not the isoform 2, PCBP 2 , in PC12 cells.Tyrosine hydroxylase (TH), 1 the rate-limiting enzyme in the biosynthesis of catecholamines, is expressed in specific populations of neurons in the central and peripheral nervous systems, in the neuroendocrine cells of the adrenal medulla and carotid body, and in cultured cell lines such as the pheochromocytomaderived PC12 cell line. Regulation of TH gene expression at the level of gene transcription is well documented. Recently, there has been growing evidence that TH mRNA is also regulated at the level of mRNA stability. TH mRNA is a stable message with a half-life that varies from 9 to 16 h in various subclones of PC12 cells (1-3). It is enhanced during differentiation of neuroblastoma cells (1) and during stimulation of the protein kinase C pathway in PC12 cells (2). In contrast, the stability of TH mRNA does not change in PC12 cells during stimulation of TH mRNA expression by dexamethasone or forskolin (3). A recent study demonstrated substantial differences in basal TH mRNA turnover rates between different neuronal populations from as short a time as 6 -7 h, in the dopaminergic neurons of the arcuate nucleus, to as long as 11-23 h, in the dopaminergic midhypothalamic neurons (4). In addition, TH mRNA is destabilized in the dopaminergic cells of the arcuate nucleus in a manner that corresponds to the rhythmic output displayed by these neurons (4).Our laboratory demonstrated that hypoxia augments the stability of TH mRNA in PC12 cells (5). We identified a 27-base-long pyrimidine-rich sequence within the TH mRNA 3Ј-untranslated region (UTR) (1552-1578 bases of TH mRNA) that binds protein factors in a hypoxia-inducible manner (hypoxia-inducible protein-binding sequence (HIPBS)) in PC12 cells (6, 7), catecholaminergic cells of the superior cervical ganglia, and the dopaminergic cells of the carotid body (8). Mutational analysis revealed that the optimal protein-binding site is represented by the motif (U/C)(C/...

Heat shock protein 70 (Hsp70) is well documented to possess general cytoprotective properties in protecting the cell against stressful and noxious stimuli. We have recently shown that expression of the stress-inducible Hsp70.3 gene in the myocardium in response to ischemic preconditioning is NF-B-dependent and necessary for the resulting late phase cardioprotection against a subsequent ischemia/reperfusion injury. Here we show that the Hsp70.3 gene product is subject to post-transcriptional regulation through parallel regulatory processes involving microRNAs and alternative polyadenylation of the mRNA transcript. First, we show that cardiac ischemic preconditioning of the in vivo mouse heart results in decreased levels of two Hsp70.3-targeting microRNAs: miR-378* and miR-711. Furthermore, an ischemic or heat shock stimulus induces alternative polyadenylation of the expressed Hsp70.3 transcript that results in the accumulation of transcripts with a shortened 3 -UTR. This shortening of the 3 -UTR results in the loss of the binding site for the suppressive miR-378* and thus renders the alternatively polyadenylated transcript insusceptible to miR-378*-mediated suppression. Results also suggest that the alternative polyadenylation-mediated shortening of the Hsp70.3 3 -UTR relieves translational suppression observed in the long 3 -UTR variant, allowing for a more robust increase in protein expression. These results demonstrate alternative polyadenylation of Hsp70.3 in parallel with ischemic or heat shock-induced up-regulation of mRNA levels and implicate the importance of this process in post-transcriptional control of Hsp70.3 expression.Heat shock (HS) 3 and the subsequent expression of heat shock proteins have long been known to possess cytoprotective properties and provide cardioprotection against ischemia/reperfusion (I/R) injury (1-3). The Hsp70 family is among the best studied of the heat shock proteins, has been shown to be induced by many cardiac preconditioning stimuli, and plays a necessary role in the second window of protection (3-6). Hsp70.1 and Hsp70.3 are two nearly identical stress-inducible Hsp70 genes present in the murine heart. The two protein products differ by only a single amino acid, but curiously, the sequence of the two genes is divergent in the regulatory regions of the gene promoter (beyond the first 270 amino acids proximal to the transcriptional start site) and within the 3Ј-untranslated region (3Ј-UTR) of the mRNA transcript. Historically, these two genes are considered to be functionally redundant.We have recently shown that NF-B-dependent expression of heat shock protein 70.3 (Hsp70.3), but not the closely related Hsp70.1, is necessary for the late phase or second window of ischemic preconditioning (IPC) cardioprotection against acute I/R in the heart (6). In fact, Hsp70.3 and Hsp70.1 appear to contribute differing functions to cell survival in the myocardium (6, 7). Thus, it is important to understand the regulation of these two genes independently. We previously reported that NF-B in...