A Major Tyrosine-phosphorylated Protein of Trypanosoma brucei Is a Nucleolar RNA-binding Protein

Das, Arpita; Peterson, Gregory C.; Kanner, Steven B.; Frevert, Ute; Parsons, Marilyn

doi:10.1074/jbc.271.26.15675

Cited by 36 publications

(27 citation statements)

References 33 publications

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“…Nopp44/46 localises to the nucleolus and in vitro binding experiments have demonstrated that this protein is capable of binding nucleic acids with a preference for poly (U). 23 Therefore, the function of RBM6 might still be comparable with the function of RBM5.…”

Section: Discussionmentioning

confidence: 97%

A comparison of genomic structures and expression patterns of two closely related flanking genes in a critical lung cancer region at 3p21.3

et al. 1999

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In the search for a tumour suppressor gene in the 3p21.3 region we isolated two genes, RBM5 and RBM6. Gene RBM5 maps to the region which is homozygously deleted in the small cell lung cancer cell line GLC20; RBM6 crosses the telomeric breakpoint of this deletion. Sequence comparison revealed that at the amino acid level both genes show 30% identity. They contain two zinc finger motifs, a bipartite nuclear signal and two RNA binding motifs, suggesting that the proteins for which RBM5 and RBM6 are coding have a DNA/RNA binding function and are located in the nucleus. Northern and Southern analysis did not reveal any abnormalities. By SSCP analysis of 16 lung cancer cell lines we found only in RBM5 a single presumably neutral mutation. By RT-PCR we demonstrated the existence of two alternative splice variants of RBM6, one including and one excluding exon 5, in both normal lung tissue and lung cancer cell lines. Exclusion of exon 5 results in a frameshift which would cause a truncated protein of 520 amino acids instead of 1123 amino acids. In normal lung tissue, the relative amount of the shorter transcript was much greater than that in the lung tumour cell lines, which raises the question whether some tumour suppressor function may be attributed to the derived shorter protein.

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Section: Discussionmentioning

confidence: 97%

A comparison of genomic structures and expression patterns of two closely related flanking genes in a critical lung cancer region at 3p21.3

et al. 1999

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“…NOPP44/46 Tyr 181 , however, was not identified, likely due to experimental limitations of that study. By immunofluorescence, phosphotyrosine proteins mostly associated with the cytoskeleton and the nucleolus, which is also the site of NOPP44/46 (32). A physiological interaction between TbPTP1 and NOPP44/46 would require cellular co-localization, and consistent with this tenet, TbPTP1 was found to associate with the cytoskeletal and nuclear fractions (10).…”

Section: Data Collectionmentioning

confidence: 90%

The Trypanosoma brucei Life Cycle Switch TbPTP1 Is Structurally Conserved and Dephosphorylates the Nucleolar Protein NOPP44/46

Chou

Jensen

Parsons

et al. 2010

Journal of Biological Chemistry

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Trypanosoma brucei adapts to changing environments as it cycles through arrested and proliferating stages in the human and tsetse fly hosts. Changes in protein tyrosine phosphorylation of several proteins, including NOPP44/46, accompany T. brucei development. Moreover, inactivation of T. brucei protein-tyrosine phosphatase 1 (TbPTP1) triggers differentiation of bloodstream stumpy forms into tsetse procyclic forms through unknown downstream effects. Here, we link these events by showing that NOPP44/46 is a major substrate of TbPTP1. TbPTP1 substrate-trapping mutants selectively enrich NOPP44/46 from procyclic stage cell lysates, and TbPTP1 efficiently and selectively dephosphorylates NOPP44/46 in vitro. To provide insights into the mechanism of NOPP44/46 recognition, we determined the crystal structure of TbPTP1. The TbPTP1 structure, the first of a kinetoplastid protein-tyrosine phosphatase (PTP), emphasizes the conservation of the PTP fold, extending to one of the most diverged eukaryotes. The structure reveals surfaces that may mediate substrate specificity and affords a template for the design of selective inhibitors to interfere with T. brucei transmission.Trypanosoma brucei causes human African trypanosomiasis or African sleeping sickness, which is marked by debilitating neurologic symptoms ranging from sensory impairment to the characteristic aberrant sleeping patterns that progress to coma. If untreated, human African trypanosomiasis is fatal. With 30,000 deaths a year and 60 million people living at risk (1), human African trypanosomiasis is a major disease burden in sub-Saharan Africa. Current drugs are ineffective and toxic, and drug resistance is becoming a growing hurdle for treatment (2).T. brucei alternates between human and tsetse fly hosts, requiring extensive and rapid physiologic adaptations. In humans, the major T. brucei population consists of the extracellular, proliferative slender form in the bloodstream, which irreversibly differentiates into the G 1 -arrested stumpy form poised for transmission to the tsetse fly. Taken up by the tsetse fly, the stumpy form differentiates into the proliferative procyclic form in the insect midgut. Eventually, the tsetse salivary gland becomes populated with metacyclic forms, which infect the human host (3). This differentiation cycle requires survival in a diverse set of environments and forms the basis for infectivity and transmission.The molecular signals, regulators, and effectors underlying this complex sequence of events are not well understood but could provide novel targets for therapeutic interference. Distinct patterns of protein tyrosine phosphorylation accompany and often precede stage progression (4), suggesting that tyrosine phosphorylation is a key mechanism of developmental regulation. Studies of the T. brucei dual specificity kinases also provide evidence that tyrosine phosphorylation regulates the trypanosome life cycle (5-7). Moreover, NOPP44/46, 2 a nucleolar RNA-binding protein required for ribosome biogenesis (8), exhibits dramatic ch...

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“…For immunoprecipitation from T. brucei, cells containing inducible expression cassettes were treated with Tet for 16-24 hours and sample lysates prepared as described [31]. Immunoprecipitations were performed as described above, using 10 8 cells per reaction.…”

Section: Immunological Methodsmentioning

confidence: 99%

Characterization of protein kinase CK2 from Trypanosoma brucei

Jensen

Kifer

Brekken

et al. 2007

Molecular and Biochemical Parasitology

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CK2 is a ubiquitous but enigmatic kinase. The difficulty in assigning a role to CK2 centers on the fact that, to date, no biologically relevant modulator of its function has been identified. One common theme revolves around a constellation of known substrates involved in growth control, compatible with its concentration in the nucleus and nucleolus. We had previously described the identification of two catalytic subunits of CK2 in Trypanosoma brucei and characterized one of them. Here we report the characterization of the second catalytic subunit, CK2α', and the identification and characterization of the regulatory subunit CK2β. All three subunits are primarily localized to the nucleolus in T. brucei. We also show that CK2β interacts with the nucleolar protein NOG1, adding to the interaction map which previously linked CK2α to the nucleolar protein NOPP44/46, which in turn associates with the rRNA binding protein p37. CK2 activity has four distinctive features: near equal affinity for GTP and ATP, heparin sensitivity, and stimulation by polyamines and polybasic peptides. Sequence comparison shows that the parasite orthologues have mutations in residues previously mapped as important in specifying affinity for GTP and stimulation by both polyamines and polybasic peptides. Studies of the enzymatic activity of the T. brucei CK2s show that both the affinity for GTP and stimulation by polyamines have been lost and only the features of heparin inhibition and stimulation by polybasic peptides are conserved.

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A Major Tyrosine-phosphorylated Protein of Trypanosoma brucei Is a Nucleolar RNA-binding Protein

Cited by 36 publications

References 33 publications

A comparison of genomic structures and expression patterns of two closely related flanking genes in a critical lung cancer region at 3p21.3

A comparison of genomic structures and expression patterns of two closely related flanking genes in a critical lung cancer region at 3p21.3

The Trypanosoma brucei Life Cycle Switch TbPTP1 Is Structurally Conserved and Dephosphorylates the Nucleolar Protein NOPP44/46

Characterization of protein kinase CK2 from Trypanosoma brucei

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