Disease relevance of PPEF1

• Despite these two unique deletions, which either lead to severely defective transcription or total absence of the retinoschisin and PPEF-1 protein, all the patients have a typical retinoschisis phenotype [1].
• Unlike the other known PPases, the expression of PP7 is not ubiquitous; PP7 was only detected in retina and retinal-derived Y-79 retinoblastoma cells [2].
• These data indicate that, in contrast to loss of rdgC function in Drosophila, elimination of PPEF function does not cause retinal degeneration in vertebrates [3].
• RNA density is present inside the capsids, suggesting that the genomic RNA of Qbeta, PP7 and AP205, analogous to MS2, contains many coat protein-binding sites in addition to the hairpin on which assembly and packaging are initiated [4].
• We propose that well-characterised bacteriophage, such as PP7 and PR772 can be used as models for mammalian viruses if the virus removal mechanism is based on size exclusion [5].

High impact information on PPEF1

• Normal light response, photoreceptor integrity, and rhodopsin dephosphorylation in mice lacking both protein phosphatases with EF hands (PPEF-1 and PPEF-2) [3].
• Finally, PPEF-2-/- retinas show normal histology at 1 year of age, and retinas from mice lacking both PPEF-1 and PPEF-2 show normal histology at 3 months of age, the latest time examined [3].
• The unique C-terminal region of PP7 contains multiple Ca2+ binding sites (i.e. EF-hand motifs) [2].
• Molecular cloning, expression, and characterization of a novel human serine/threonine protein phosphatase, PP7, that is homologous to Drosophila retinal degeneration C gene product (rdgC) [2].
• The activity of recombinant PP7 is dependent on Mg2+ and is activated by calcium (IC50 approximately equal to 250 microM) [2].

Biological context of PPEF1

• The fragments corresponding to the second exons of PPEF1 and PPEF2, containing the IQ motifs, are sufficient for specific Ca(2+)-dependent interaction with CaM both in vivo and in vitro [6].
• Yet, recent identification of protein phosphatases with EF-hand domains (PPEF/rdgC) point to the existence of another group of Ca(2+)-dependent protein phosphatases [6].
• We have tested the gene, designated PPEF in humans, as a candidate gene in RS patients using RT-PCR and the protein truncation test on RNA and SSCP on DNA [7].
• In contrast, expression of RdgC/PPEF phosphatases and PP7 is confined primarily to specialised sensory cells in animals and plants, respectively, which may be indicative of their more specialised roles in sensory signal transduction [8].
• In L. major and T. brucei, the PPEF-like phosphatases are encoded by single-copy genes and are constitutively expressed in all parasite life cycle stages [9].

Anatomical context of PPEF1

• PPEF-1 transcripts are present at low levels in the retina, while PPEF-2 transcripts and PPEF-2 protein are abundant in photoreceptors [3].
• Effects of cytoskeleton-disrupting drugs indicate that cytoskeleton may be required for efficient PP7 [10].
• The pinealocytes, parenchymal cells of the pineal body, were labeled with five, neuronal and seven pineal monoclonal (from PP1 to PP7) antibodies in the normal pineal bodies [11].

Associations of PPEF1 with chemical compounds

• A novel serine/threonine protein phosphatase (PPase) designated PP7 was identified from cDNA produced from human retina RNA [2].
• Expression of recombinant human PP7 in baculovirus-infected SF21 insect cells produces an active soluble enzyme that is capable of utilizing phosphohistone and p-nitrophenyl phosphate as substrates [2].
• Western blots of culture media incubated with antibodies against human placental proteins (PP) demonstrated that PP4 and PP7 were released throughout the cycle, while PP14 was present only at the late luteal stage of the cycle [12].
• Deletion of a potential nuclear localization signal in the first insert in the catalytic domain, as well as exposure to the dark, cold, high salinity and abscisic acid failed to prevent nuclear localization of PP7 [10].
• Using designed variants of the wild-type RNA, and selection of binding-competent sequences from random RNA sequence libraries (i.e. SELEX) we find that tight binding to PP7 coat protein is favored by the existence of an 8 bp hairpin with a bulged purine on its 5' side separated by 4 bp from a 6 nt loop having the sequence Pu-U-A-G/U-G-Pu [13].

Other interactions of PPEF1

• Unexpectedly this large deletion abolishes exons of three adjacent genes: serine-threonine phosphatase gene (PPEF-1)/serine-threonine protein phosphatase gene (PP7), retinoschisis gene (RS1), and serine-threonine kinase gene (STK9) [1].

Analytical, diagnostic and therapeutic context of PPEF1

• We now addressed the intracellular location of Arabidopsis thaliana PP7 using GFP fusions and confocal laser scanning microscopy [10].

References