Disease relevance of PPP1R8

• In H1299 and A549 lung cancer cells, hARD1-silencing RNA inhibited cell proliferation and induced G(1) arrest [1].
• In addition, infection of HeLa MAGI cells with adeno-associated virus-NIPP1 prior to the infection with HIV-1 significantly reduced the level of HIV-1 replication [2].
• ARD 1 mRNAs of 3.7 and 4.1 kilobases were detected in all rat tissues as well as in mouse and rabbit brain, human fibroblasts, and human neuroblastoma cells but not in HL-60 cells [3].
• Here we demonstrate that the level of human ARD1 (hARD1) protein is not decreased in hypoxia [4].
• However, recombinant hARD1 from Escherichia coli was produced with partial N-terminal acetylation and was observed to undergo slow self-mediated N-terminal acetylation [5].

High impact information on PPP1R8

• Deletion of the RING region or point mutations within the RING sequence abolished ARD1 E3 ligase activity [6].
• The beta-catenin binding and acetylation by hARD1 were observed in vitro [1].
• Therefore, it is suggested that hARD1 participates in proliferation of lung cancer cells via the activation of beta-catenin [1].
• Arrest defective 1 (ARD1), an acetyltransferase, is essential for the yeast life cycle [1].
• This splicing defect was also seen with a kinase-dead mutant but was absent after mutation (T478A) of the NIPP1 binding site of MELK, indicating a mediatory role for NIPP1 [7].

Biological context of PPP1R8

• Possible missense mutations of the PPP1R5, PPP1R7 and PPP1R8 genes were detected in one (2%), two (4%) and one (2%) cell line, respectively [8].
• PPP1R8 (25.2 kb) is composed of seven exons and encodes four different transcripts, as determined from cDNA library screening, reverse transcriptase-PCR (RT-PCR) and/or EST (expressed sequence tag) database search analysis [9].
• PPP1R8 is an authentic NIPP-1 gene and was localized to chromosome 1p35 [9].
• Properties and phosphorylation sites of baculovirus-expressed nuclear inhibitor of protein phosphatase-1 (NIPP-1) [10].
• The bacterially expressed central third of NIPP-1 completely inhibited the type-1 catalytic subunit, but displayed a reduced inhibitory potency after phosphorylation by protein kinase A and casein kinase 2 [11].

Anatomical context of PPP1R8

• The nuclear protein NIPP1 (nuclear inhibitor of protein Ser/Thr phosphatase-1) interacts with the splicing factors SAP155 and CDC5L and is involved in a late step of spliceosome assembly [12].
• NIPP-1alpha mRNA represents the major transcript in human tissues and various cell lines, and encodes a polypeptide of 351 residues that only differs from the previously cloned calf thymus NIPP-1 by a single residue [9].
• CDC5L and NIPP1 co-localized in nuclear speckles in COS-1 cells [13].
• When expressed in COS-1 or HeLa cells, the FHA domain of NIPP1 did not affect the number of cells in the G(2)/M transition [13].
• Translation of NIPP-1 mRNA in reticulocyte lysates resulted in the accumulation of both intact NIPP-1 and a smaller polypeptide generated by alternative initiation at the codon corresponding to Met143 [11].

Associations of PPP1R8 with chemical compounds

• We report here that the phosphothreonine-binding Forkhead-associated domain of NIPP1 interacts with the cell cycle-regulated protein Ser/Thr kinase MELK (maternal embryonic leucine zipper kinase) [7].
• Binding of wild-type and mutant phosphatases to immobilized microcystin-LR, NIPP-1, and I-2 established that the beta12-beta13 loop was essential for the association of PP1 with toxins and the protein inhibitors [14].
• Type-1 protein serine/threonine phosphatases (PP1) are uniquely inhibited by the mammalian proteins, inhibitor-1 (I-1), inhibitor-2 (I-2), and nuclear inhibitor of PP1 (NIPP-1) [14].
• Finally, NIPP1(-/-) mouse embryos showed a nuclear hyperphosphorylation on threonine, consistent with a role for NIPP1 in the nuclear targeting and/or retention of PP1 [15].
• Deletion of C-terminal sequences that included the beta12-beta13 loop attenuated the inhibition of the resulting PP1alpha catalytic core by I-1, I-2, NIPP-1, and several toxins, including tautomycin, microcystin-LR, calyculin A, and okadaic acid [14].

Physical interactions of PPP1R8

• We show here that the FHA domain of NIPP1 interacts in vitro and in vivo with a TP dipeptide-rich fragment of the splicing factor SAP155/SF3b(155), a component of the U2 small nuclear ribonucleoprotein particle [16].

Regulatory relationships of PPP1R8

• Remarkably, while both NIPP1 domains inhibited the phosphorylase phosphatase activity of PP1(C) independently, mutation of either domain completely abolished the ability of NIPP1 to inhibit the dephosphorylation of myelin basic protein [17].

Other interactions of PPP1R8

• We report here the cloning and structural characterization of the human NIPP-1 genes, designated PPP1R8P and PPP1R8 in human gene nomenclature [9].
• Inhibition of spliceosome assembly by the cell cycle-regulated protein kinase MELK and involvement of splicing factor NIPP1 [7].
• NIPP1-mediated interaction of protein phosphatase-1 with CDC5L, a regulator of pre-mRNA splicing and mitotic entry [13].
• We discuss how the interaction between NIPP1 and SAP155 could contribute to spliceosome (dis)assembly and the catalytic steps of splicing [16].
• The in vitro splicing of beta-globin pre-mRNA was not affected by exogenous wild type NIPP1 but was blocked by mutants that lacked residues 225-329 [18].

Analytical, diagnostic and therapeutic context of PPP1R8

• Site-directed mutagenesis furthermore showed that this spliceosomal function of NIPP1 was unrelated to its ability to bind PP1 or RNA [18].
• Furthermore, an interaction between CDC5L, NIPP1, and PP1 in rat liver nuclear extracts could be demonstrated by co-immunoprecipitation and/or co-purification experiments [13].
• Molecular cloning of NIPP-1, a nuclear inhibitor of protein phosphatase-1, reveals homology with polypeptides involved in RNA processing [11].
• Western blotting with antibodies against the COOH terminus of NIPP-1, however, showed a single polypeptide of 47 kDa, which was enriched in the nucleus [11].
• Closer sequence analysis revealed novel alternatively spliced variants of Nek2A and NIPP1, which we designated Nek2A-T and NIPP1-T, respectively [19].

References