Low resolution structure of the human α4 protein (IgBP1) and studies on the stability of α4 and of its yeast ortholog Tap42

Smetana, Juliana Helena Costa; Oliveira, C. L. P.; Jablonka, Willy; Pertinhez, Thelma A.; Carneiro, Flavia Raquel Gonçalves; Montero-Lomelı́, Mónica; Torriani, Iris Concepcion Linares de; Zanchin, Nilson Ivo Tonin

doi:10.1016/j.bbapap.2006.01.018

Cited by 19 publications

(26 citation statements)

References 43 publications

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“…In their native tandem configuration, the activity of the RING domain is significantly enhanced by the B-boxes implying cooperativity in function (19). The interaction between ␣4 and MID1 is mediated by the C-terminal domain (residues 236 -280) of ␣4 and the Bbox1 domain of MID1, whereas the N-terminal domain (residues 1-236) of ␣4 is involved in binding PP2Ac (15,20,21).…”

Section: Alpha4 (␣4) Is a Key Regulator Of Protein Phosphatase 2a (Ppmentioning

confidence: 99%

“…With respect to PP2A, ␣4 binds the catalytic subunit (PP2Ac), at which time it is thought to displace the scaffolding (PP2Aa, PR65) and regulatory subunits (PP2Ab) that typically constitute the PP2A heterotrimeric complex (6,(11)(12)(13). Under growthpromoting conditions, ␣4 down-regulates PP2A activity within the mTOR signaling pathway, resulting in the downstream activation of eIF-4E and S6 kinase and the initiation of cell cycle progression (4,14,15).…”

Section: Alpha4 (␣4) Is a Key Regulator Of Protein Phosphatase 2a (Ppmentioning

confidence: 99%

“…Expression and Purification of Recombinant Proteins-Cells expressing full-length ␣4 (His 6 -␣4), the N-terminal domain (His 6 -␣4N, residues 1-235), and the C-terminal domain (His 6 -␣4C, residues 236 -339) were grown in LB media at 37°C to an A 600 of ϳ0.6 and induced with 1 mM isopropyl 1-thio-␤-D-galactopyranoside for 18 h at 16°C (15). Harvested cells were resuspended in buffer 50 mM Tris, 200 mM NaCl, 10% glycerol (pH 8.0) with protease inhibitors and lysed with lysozyme.…”

Section: Generation Of Stable Mdck Cellmentioning

confidence: 99%

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The MID1 E3 Ligase Catalyzes the Polyubiquitination of Alpha4 (α4), a Regulatory Subunit of Protein Phosphatase 2A (PP2A)

Huang²,

Zaghlula

et al. 2013

Journal of Biological Chemistry

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Background: IGBP1/␣4 interacts with microtubule-associated MID1 to regulate PP2A within the mTOR pathway. Results: MID1 catalyzes the polyubiquitination and degradation of ␣4, demonstrating for the first time a mechanism for ␣4 regulation. Conclusion:The tandem RING-Bbox domains are required for ␣4 polyubiquitination and degradation. Significance: Ectopic overexpression of IGBP1/␣4 transforms cells. Ubiquitination of ␣4 impacts the stability and activity level of PP2A.

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Section: Alpha4 (␣4) Is a Key Regulator Of Protein Phosphatase 2a (Ppmentioning

confidence: 99%

Section: Alpha4 (␣4) Is a Key Regulator Of Protein Phosphatase 2a (Ppmentioning

confidence: 99%

Section: Generation Of Stable Mdck Cellmentioning

confidence: 99%

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The MID1 E3 Ligase Catalyzes the Polyubiquitination of Alpha4 (α4), a Regulatory Subunit of Protein Phosphatase 2A (PP2A)

Huang²,

Zaghlula

et al. 2013

Journal of Biological Chemistry

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“…Both Alpha4 and Tap42 consist of an N-terminal domain that contains the residues important for PP2Ac binding (20) and a C-terminal domain that is protease-sensitive and intrinsically disordered (21). The C-terminal domain of Alpha4 binds Mid1, a putative E3 ligase (12,22).…”

Section: Pp2amentioning

confidence: 99%

The E3 Ubiquitin Ligase- and Protein Phosphatase 2A (PP2A)-binding Domains of the Alpha4 Protein Are Both Required for Alpha4 to Inhibit PP2A Degradation

Lenoue-Newton¹,

Watkins²,

Zou

et al. 2011

Journal of Biological Chemistry

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Protein phosphatase 2A (PP2A) is regulated through a variety of mechanisms, including post-translational modifications and association with regulatory proteins. Alpha4 is one such regulatory protein that binds the PP2A catalytic subunit (PP2Ac) and protects it from polyubiquitination and degradation. Alpha4 is a multidomain protein with a C-terminal domain that binds Mid1, a putative E3 ubiquitin ligase, and an N-terminal domain containing the PP2Ac-binding site. In this work, we present the structure of the N-terminal domain of mammalian Alpha4 determined by x-ray crystallography and use double electronelectron resonance spectroscopy to show that it is a flexible tetratricopeptide repeat-like protein. PP2A3 is a ubiquitous serine/threonine phosphatase involved in the regulation of numerous cell signaling pathways and cellular functions, including proliferation, cytoskeletal rearrangement, apoptosis, and cell migration (1-3). Several pathologies have been linked to dysregulation of PP2Ac, including Alzheimer disease, cancer, and diabetes (4 -8). The activity of PP2Ac is tightly controlled in vivo via association with regulatory subunits, interactions with other cellular proteins, and various post-translational modifications (9 -12). PP2A regulatory subunits play a critical role in determining phosphatase activity and substrate selectivity, as well as directing the subcellular localization of the PP2A holoenzyme (3). PP2A exists primarily as a heterotrimeric holoenzyme consisting of a structural A-subunit, a variable regulatory B-subunit, and PP2Ac. However, an atypical pool of PP2Ac exists in complex with the regulatory subunit Alpha4 that binds directly to PP2Ac in the absence of the A-and B-subunits (13-16). Recent studies have shown that Alpha4 plays a crucial role in the control of PP2A ubiquitination and stability (12,17,18).Alpha4, a multidomain protein with similarity to Tap42 from yeast, was initially discovered as a 52-kDa phosphoprotein in B-cell receptor complexes (16,19). Both Alpha4 and Tap42 consist of an N-terminal domain that contains the residues important for PP2Ac binding (20) and a C-terminal domain that is protease-sensitive and intrinsically disordered (21). The C-terminal domain of Alpha4 binds Mid1, a putative E3 ligase (12,22). Alpha4 regulates all three type 2A protein phosphatases (PP2Ac, PP4, and PP6), modulating both catalytic activity and expression levels (13,14,17,23). In addition to its association with PP2A family members, Alpha4 associates and co-localizes with Mid1, a putative E3 ubiquitin ligase thought to facilitate PP2Ac polyubiquitination (12,22). The C terminus of Alpha4 and the B-box1 domain of the Mid1 protein mediate the association between Mid1 and Alpha4 (12,22). Mutations in Mid1 have been linked to Opitz syndrome, a developmental disorder (24,25). At the cellular level, mutations in Mid1 lead to decreases in ubiquitination and degradation of PP2Ac, especially microtubule-associated PP2Ac (12, 26).Alpha4 serves as a scaffold for PP2Ac and Mid1 and protects PP2Ac fr...

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“…Many proteins have been found to form complexes with PP2A subunits and in turn regulate the enzyme activity and biological functions. As a regulatory protein of PP2A, a4 (Tap42 in yeast), encoded by human IGBP1 gene, directly binds to the PP2A catalytic subunit (PP2Ac) by its N-terminal domain (Smetana et al, 2006), altering catalytic activity and substrate specificity (Chen et al, 1998). Binding of a4 to PP2Ac displaces PP2Ac from A and B subunits owing to an overlap in the binding site on PP2Ac (Goldberg, 1999).…”

Section: Introductionmentioning

confidence: 99%

α4 is highly expressed in carcinogen-transformed human cells and primary human cancers

et al. 2011

Oncogene

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A regulator of the protein phosphatase 2A (PP2A), a4, has been implicated in a variety of functions that regulate many cellular processes. To explore the role of a4 in human cell transformation and tumorigenesis, we show that a4 is highly expressed in human cells transformed by chemical carcinogens including benzo(a)pyrene, aflatoxin B 1 , N-methyl-N 0 -nitro-N-nitrosoguanidine, nickel sulfate and in several hepatic and lung cancer cell lines. In addition, overexpression of a4 was detected in 87.5% (74/80) of primary hepatocellular carcinomas, 84.0% (21/25) of primary lung cancers and 81.8% (9/11) of primary breast cancers, indicating that a4 is ubiquitously highly expressed in human cancer. Functional studies revealed that elevated a4 expression results in an increase in cell proliferation, promotion of cell survival and decreased PP2A-attributable activity. Importantly, ectopic expression of a4 permits non-transformed human embryonic kidney cells (HEKTER) and L02R cells to form tumors in immunodeficient mice. Furthermore, we show that the highly expressed a4 in transformed cells or human tumors is not regulated by DNA hypomethylation. A microRNA, miR-34b, that suppresses the expression of a4 through specific binding to the 3 0 -untranslated region of a4 is downregulated in transformed or human lung tumors. Taken together, these observations identify that a4 possesses an oncogenic function. Reduction of PP2A activity due to an enhanced a4-PP2A interaction contributes directly to chemical carcinogen-induced tumorigenesis.

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Low resolution structure of the human α4 protein (IgBP1) and studies on the stability of α4 and of its yeast ortholog Tap42

Cited by 19 publications

References 43 publications

The MID1 E3 Ligase Catalyzes the Polyubiquitination of Alpha4 (α4), a Regulatory Subunit of Protein Phosphatase 2A (PP2A)

The MID1 E3 Ligase Catalyzes the Polyubiquitination of Alpha4 (α4), a Regulatory Subunit of Protein Phosphatase 2A (PP2A)

The E3 Ubiquitin Ligase- and Protein Phosphatase 2A (PP2A)-binding Domains of the Alpha4 Protein Are Both Required for Alpha4 to Inhibit PP2A Degradation

α4 is highly expressed in carcinogen-transformed human cells and primary human cancers

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