The LIMD1 protein bridges an association between the prolyl hydroxylases and VHL to repress HIF-1 activity

School of Biomedical Sciences, University of Nottingham, Queen's Medical Centre, NG7 2UH, UK.
Nature Cell Biology (Impact Factor: 19.68). 02/2012; 14(2):201-8. DOI: 10.1038/ncb2424
Source: PubMed


There are three prolyl hydroxylases (PHD1, 2 and 3) that regulate the hypoxia-inducible factors (HIFs), the master transcriptional regulators that respond to changes in intracellular O(2) tension. In high O(2) tension (normoxia) the PHDs hydroxylate two conserved proline residues on HIF-1α, which leads to binding of the von Hippel-Lindau (VHL) tumour suppressor, the recognition component of a ubiquitin-ligase complex, initiating HIF-1α ubiquitylation and degradation. However, it is not known whether PHDs and VHL act separately to exert their enzymatic activities on HIF-1α or as a multiprotein complex. Here we show that the tumour suppressor protein LIMD1 (LIM domain-containing protein) acts as a molecular scaffold, simultaneously binding the PHDs and VHL, thereby assembling a PHD-LIMD1-VHL protein complex and creating an enzymatic niche that enables efficient degradation of HIF-1α. Depletion of endogenous LIMD1 increases HIF-1α levels and transcriptional activity in both normoxia and hypoxia. Conversely, LIMD1 expression downregulates HIF-1 transcriptional activity in a manner depending on PHD and 26S proteasome activities. LIMD1 family member proteins Ajuba and WTIP also bind to VHL and PHDs 1 and 3, indicating that these LIM domain-containing proteins represent a previously unrecognized group of hypoxic regulators.

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    • "to hypoxia (Foxler et al., 2012), hippo signaling (Das Thakur et al., 2010), PIP2 signaling (Kisseleva et al., 2005) and stress fiber maintenance (Smith et al., 2010; Hoffman et al., 2012). Molecular genetic analysis in mouse suggests that vertebrate zyxin family members assume functionally redundant cellular roles, since mouse knockouts of LPP and zyxin exhibit few overt phenotypic abnormalities (Hoffman et al., 2003; Vervenne et al., 2009), whereas Drosophila mutants are inviable (Das Thakur et al., 2010; Renfranz et al., 2010). "
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    ABSTRACT: We describe the identification of zyxin as a regulator of synapse maintenance in mechanosensory neurons in C. elegans. zyx-1 mutants lacked PLM mechanosensory synapses as adult animals. However, most PLM synapses initially formed during development but were subsequently lost as the animals developed. Vertebrate zyxin regulates cytoskeletal responses to mechanical stress in culture. Our work provides in vivo evidence in support of such a role for zyxin. In particular, zyx-1 mutant synaptogenesis phenotypes were suppressed by disrupting locomotion of the mutant animals, suggesting that zyx-1 protects mechanosensory synapses from locomotion-induced forces. In cultured cells, zyxin is recruited to focal adhesions and stress fibers via C-terminal LIM domains and modulates cytoskeletal organization via the N-terminal domain. The synapse-stabilizing activity was mediated by a short isoform of ZYX-1 containing only the LIM domains. Consistent with this notion, PLM synaptogenesis was independent of α-actinin and ENA-VASP, both of which bind to the N-terminal domain of zyxin. Our results demonstrate that the LIM domain moiety of zyxin functions autonomously to mediate responses to mechanical stress and provide in vivo evidence for a role of zyxin in neuronal development.
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    • "Under normal oxygen levels, HIF-1α is unstable because PHDs use molecular oxygen as a substrate to hydroxylate proline residues of HIF-1α. The hydroxylated HIF-1α is recognized by the von Hippel-Lindau tumor suppressor (VHL), and targeted for proteasomal degradation [24,26,32]. It has been demonstrated that CoCl2 is an effective inducer of chemical hypoxia by inhibiting the activity of PHDs and preventing degradation of HIF-1α protein [25,33]. "
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    ABSTRACT: Mipu1 (myocardial ischemic preconditioning up-regulated protein 1), recently identified in our lab, is a novel zinc-finger transcription factor which is up-regulated during ischemic preconditioning. However, it is not clear what transcription factor contributes to its inducible expression. In the present study, we reported that HIF-1 regulates the inducible expression of Mipu1 which is involved in the cytoprotection of HIF-1α against oxidative stress by inhibiting Bax expression. Our results showed that the inducible expression of Mipu1 was associated with the expression and activation of transcription factor HIF-1 as indicated by cobalt chloride (CoCl2) treatment, HIF-1α overexpression and knockdown assays. EMSA and luciferase reporter gene assays showed that HIF-1α bound to the hypoxia response element (HRE) within Mipu1 promoter region and promoted its transcription. Moreover, our results revealed that Mipu1 inhibited the expression of Bax, an important pro-apoptosis protein associated with the intrinsic pathway of apoptosis, elevating the cytoprotection of HIF-1 against hydrogen peroxide (H2O2)-mediated injury in H9C2 cells. Our findings implied that Bax may be a potential target gene of transcription factor Mipu1, and provided a novel insight for understanding the cytoprotection of HIF-1 and new clues for further elucidating the mechanisms by which Mipu1 protects cell against pathological stress.
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    • "The up-regulation of this TF in the preeclamptic placenta seems coherent with the detection of an over-representation of TFBS for E2F1 among the down-regulated genes. On the other hand, LIMD1 has been recently involved in the regulation of the hypoxia response through a mechanism involving HIF1-α degradation [83]. LIMD1 up-regulation in the preeclamptic placenta might result from a feed-back mechanism aiming to regulate the transcriptional activity of the HIF complex. "
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