Biomedical subjects

Peter H King

Publications and source records attributed to Peter H King.

9 recordsLinked to original sources

PubMed2005

Docking and rolling, a model of how the mitotic motor Eg5 works.

Whereas kinesin I is designed to transport cargoes long distances in isolation, a closely related kinesin motor, Eg5, is designed to generate a sustained opposing force necessary for proper mitotic spindle formation. Do the very different roles for these evolutionarily related motors translate into differences in how they generate movement? We have addressed this question by examining when in the ATPase cycle the Eg5 motor domain and neck linker move through the use of a series of novel spectroscopic probes utilizing fluorescence resonance energy transfer, and we have compared our results to kinesin I. Our results are consistent with a model in which movement in Eg5 occurs in two sequential steps, an ATP-dependent docking of the neck linker, followed by a rotation or "rolling" of the entire motor domain on the microtubule surface that occurs with ATP hydrolysis. These two forms of movement are consistent with the functions of a motor designed to generate sustained opposing force, and hence, our findings support the argument that the mechanochemical features of a molecular motor are shaped more by the demands placed on it than by its particular family of origin.

Adenosine Diphosphate↗

PubMed2005

Novel DNA-binding properties of the RNA-binding protein TIAR.

TIA-1 related protein binds avidly to uridine-rich elements in mRNA and pre-mRNAs of a wide range of genes, including interleukin (IL)-8 and vascular endothelial growth factor (VEGF). The protein has diverse regulatory roles, which in part depend on the locus of binding within the transcript, including translational control, splicing and apoptosis. Here, we observed selective and potent inhibition of TIAR-RNP complex formation with IL-8 and VEGF 3'-untranslated regions (3'-UTRs) using thymidine-rich deoxyoligonucleotide (ODN) sequences derived from the VEFG 3'-UTR. We show by ultraviolet crosslinking and electrophoretic mobility shift assays that TIAR can bind directly to single-stranded, thymidine-rich ODNs but not to double-stranded ODNs containing the same sequence. TIAR had a nearly 6-fold greater affinity for DNA than RNA (K(d)app = 1.6x10(-9) M versus 9.4 x 10(-9) M). Truncation of TIAR indicated that the high affinity DNA-binding site overlaps with the RNA-binding site involving RNA recognition motif 2 (RRM2). However, RRM1 alone could also bind to DNA. Finally, we show that TIAR can be displaced from single-stranded DNA by active transcription through the binding site. These results provide a potential mechanism by which TIAR can shuttle between RNA and DNA ligands.

3' Untranslated Regions↗

PubMed2005

The ELAV RNA-stability factor HuR binds the 5'-untranslated region of the human IGF-IR transcript and differentially represses cap-dependent and IRES-mediated translation.

The type I insulin-like growth factor receptor (IGF-IR) is an integral component in the control of cell proliferation, differentiation and apoptosis. The IGF-IR mRNA contains an extraordinarily long (1038 nt) 5'-untranslated region (5'-UTR), and we have characterized a diverse series of proteins interacting with this RNA sequence which may provide for intricate regulation of IGF-IR gene expression at the translational level. Here, we report the purification and identification of one of these IGF-IR 5'-UTR-binding proteins as HuR, using a novel RNA crosslinking/RNase elution strategy. Because HuR has been predominantly characterized as a 3'-UTR-binding protein, enhancing mRNA stability and generally increasing gene expression, we sought to determine whether HuR might serve a different function in the context of its binding the IGF-IR 5'-UTR. We found that HuR consistently repressed translation initiation through the IGF-IR 5'-UTR. The inhibition of translation by HuR was concentration dependent, and could be reversed in trans by addition of a fragment of the IGF-IR 5'-UTR containing the HuR binding sites as a specific competitor, or abrogated by deletion of the third RNA recognition motif of HuR. We determined that HuR repressed translation initiation through the IGF-IR 5'-UTR in cells as well, and that siRNA knockdown of HuR markedly increased IGF-IR protein levels. Interestingly, we also found that HuR potently inhibited IGF-IR translation mediated through internal ribosome entry. Kinetic assays were performed to investigate the mechanism of translation repression by HuR and the dynamic interplay between HuR and the translation apparatus. We found that HuR, occupying a cap-distal position, significantly delayed translation initiation mediated by cap-dependent scanning, but was eventually displaced from its binding site, directly or indirectly, as a consequence of ribosomal scanning. However, HuR perpetually blocked the activity of the IGF-IR IRES, apparently arresting the IRES-associated translation pre-initiation complex in an inactive state. This function of HuR as a 5'-UTR-binding protein and dual-purpose translation repressor may be critical for the precise regulation of IGF-IR expression essential to normal cellular homeostasis.

5' Untranslated Regions↗

PubMed2005

IL-1beta induces stabilization of IL-8 mRNA in malignant breast cancer cells via the 3' untranslated region: Involvement of divergent RNA-binding factors HuR, KSRP and TIAR.

IL-8 plays an integral role in promoting the malignant phenotype in breast cancer, and its production is directly influenced by inflammatory cytokines in the tumor microenvironment. Here, we show that activation of IL-1beta receptors on malignant HS578t and MDA-MB-231 breast cancer cells strongly induces IL-8 expression and that RNA stabilization is persistently activated at least 12-24 hr after stimulation. SB 203580 and rapamycin reversed the RNA stabilization effect of IL-1beta in a dose-dependent manner, suggesting involvement of the p38/MAP kinase and mTOR pathways. A luciferase reporter assay indicated that the stabilization effect was dependent on cis elements in the 3'-untranslated region (UTR) of the IL-8 transcript. By UV cross-linking, we identified multiple cellular factors that interact with the IL-8 3'UTR, ranging 34-76 kDa. Immunoprecipitation analysis indicated that HuR, KSRP and TIAR bound to one or more loci in the 3'UTR. While the cross-linking patterns were similar, quantitative immunoprecipitation of native IL-8 RNA from IL-1beta-stimulated cytoplasmic extract revealed a 20-fold greater association of transcript with the stabilizing factor HuR vs. the destabilizing factor KSRP. In conclusion, IL-1beta is a potent cytokine stimulus for IL-8 RNA stabilization in breast cancer cells, possibly by enhanced binding of cytoplasmic HuR to the 3'UTR.

3' Untranslated Regions↗

PubMed2003

Tumor necrosis factor alpha induces angiogenic factor up-regulation in malignant glioma cells: a role for RNA stabilization and HuR.

Malignant glioma (MG) cells up-regulate angiogenic factor expression in response to different extracellular signals such as hypoxia and cytokines. This up-regulation in turn promotes angiogenesis and tumor progression. Posttranscriptional gene regulation has been implicated as one mechanism for this tumor response, and we have previously shown that HuR, a protein associated with RNA stabilization, is overexpressed in MGs (L. B. Nabors et al., Cancer Res., 61: 2154-2161, 2001). Here, we demonstrate a marked up-regulation (RNA and protein) of tumor necrosis factor alpha (TNF-alpha), interleukin 8, and, to a lesser extent, vascular endothelial growth factor in U251 glioma cells after stimulation with TNF-alpha. RNA kinetic studies indicated that TNF-alpha induced the stabilization of all three transcripts. Using a luciferase reporter assay, we demonstrate that the AU-rich elements (AREs) in the 3'-untranslated region of these genes significantly contribute to this posttranscriptional regulation. UV cross-linking and immunoprecipitation with glioma extracts indicate that HuR binds to all three AREs. When HuR is overexpressed in glioma cells, there is enhanced RNA stabilization of all three angiogenic factor transcripts with a concomitant increase in mRNA and protein expression (up to 7-fold). These findings indicate that TNF-alpha up-regulates angiogenic factor expression in MG cells and that RNA stabilization, via the AREs in the 3'-untranslated region, contributes to this up-regulation.

3' Untranslated Regions↗

PubMed2003

Stepping and stretching. How kinesin uses internal strain to walk processively.

The ability of kinesin to travel long distances on its microtubule track without dissociating has led to a variety of models to explain how this remarkable degree of processivity is maintained. All of these require that the two motor domains remain enzymatically "out of phase," a behavior that would ensure that, at any given time, one motor is strongly attached to the microtubule. The maintenance of this coordination over many mechanochemical cycles has never been explained, because key steps in the cycle could not be directly observed. We have addressed this issue by applying several novel spectroscopic approaches to monitor motor dissociation, phosphate release, and nucleotide binding during processive movement by a dimeric kinesin construct. Our data argue that the major effect of the internal strain generated when both motor domains of kinesin bind the microtubule is to block ATP from binding to the leading motor. This effect guarantees the two motor domains remain out of phase for many mechanochemical cycles and provides an efficient and adaptable mechanism for the maintenance of processive movement.

Adenosine Diphosphate↗

PubMed2002

Measuring kinesin's first step.

A variety of models have recently emerged to explain how the molecular motor kinesin is able to maintain processive movement for over 100 steps. Although these models differ in significant features, they all predict that kinesin's catalytic domains intermittently separate from each other as the motor takes 8-nm steps along the microtubule. Furthermore, at some point in this process, one molecule of ATP is hydrolyzed per step. However, exactly when hydrolysis and product release occur in relation to this forward step have not been established. Furthermore, the rate at which this separation occurs as well as the speed of motor stepping onto and release from the microtubule have not been measured. In the absence of this information, it is difficult to critically evaluate competing models of kinesin function. We have addressed this issue by developing spectroscopic probes whose fluorescence is sensitive to motor-motor separation or microtubule binding. The kinetics of these fluorescence changes allow us to directly measure how fast kinesin steps onto and releases from the microtubule and provide insight into how processive movement is maintained by this motor.

Adenosine Diphosphate↗

PubMed2002

Human cytomegalovirus infection and expression in human malignant glioma.

Malignant gliomas are the most common primary brain tumors in adults, have no known etiology, and are generally rapidly fatal despite current therapies. Human cytomegalovirus (HCMV) is beta-herpesvirus trophic for glial cells that persistently infects 50-90% of the adult human population. HCMV can be reactivated under conditions of inflammation and immunosuppression, and HCMV gene products can dysregulate multiple cellular pathways involved in oncogenesis. Here we show that a high percentage of malignant gliomas are infected by HCMV and multiple HCMV gene products are expressed in these tumors. These data are the first to show an association between HCMV and malignant gliomas and suggest that HCMV may play an active role in glioma pathogenesis.

Astrocytoma↗

PubMed2002

Porphyria presenting with bilateral radial motor neuropathy: evidence of a novel gene mutation.

The authors identified a novel mutation of the porphobilinogen deaminase (PBG-D) gene in a patient with acute intermittent porphyria presenting with severe and bilateral axonal radial motor neuropathy. Electrophysiologic studies revealed prominent involvement of distal radial nerves in the setting of mild polyneuropathy. Analysis of the PBG-D gene revealed a single base-pair insertion (887insA) in exon 14.

Adult↗