Validation of trans-acting elements that promote exon 7 skipping of SMN2 in SMN2-GFP stable cell line

Spinal muscular atrophy is a genetic disease in which the SMN1 gene is deleted. The SMN2 gene exists in all of the patients. Alternative splicing of these two genes are different. More than 90% of exon 7 included form is produced from SMN1 pre-mRNA, whereas only ～20% of exon 7 included form is produced from SMN2 pre-mRNA. Only exon 7 inclusion form produces functional protein. Exon 7 skipped SMN isoform is unstable. Here we constructed a GFP reporter system that recapitulates the alternative splicing of SMN1 and SMN2 pre-mRNA. We designed a system in which GFP protein is expressed only when exon 7 of is included in alternative splicing. The stable cell that expresses SMN1-GFP produces ～4 times more GFP protein than the stable cell line that expresses SMN2-GFP; as demonstrated by microscopy, FACS analysis and immunoblotting. In addition the ratio of exon 7 inclusion and skipping of SMN1-GFP and SMN2-GFP pre-mRNA was similar to endogenous SMN1 and SMN2 pre-mRNA as shown in RT-PCR. Furthermore the knockdown with hnRNP A1 shRNA, a known protein which promotes exon 7 skipping of SMN2, induces exon 7 inclusion of exon 7 in SMN2-GFP pre-mRNA in SMN2-GFP cell line. We conclude that we have established the stable cell lines that recapitulate alternative splicing of the SMN1 and SMN2 genes. The stable cell line can be used to identify the trans-acting elements with siRNA.     

The multivalent PDZ domain-containing protein PDZK1 regulates transport activity of renal urate-anion exchanger URAT1 via its C terminus

The urate-anion exchanger URAT1 is a member of the organic anion transporter (OAT) family that regulates blood urate level in humans and is targeted by uricosuric and antiuricosuric agents. URAT1 is expressed only in the kidney, where it is thought to participate in tubular urate reabsorption. We found that the multivalent PDZ (PSD-95, Drosophila discs-large protein, Zonula occludens protein 1) domain-containing protein, PDZK1 interacts with URAT1 in a yeast two-hybrid screen. Such an interaction requires the PDZ motif of URAT1 in its extreme intracellular C-terminal region and the first, second, and fourth PDZ domains of PDZK1 as identified by yeast two-hybrid assay, in vitro binding assay and surface plasmon resonance analysis (K(D) = 1.97-514 nM). Coimmunoprecipitation studies revealed that the wild-type URAT1, but not its mutant lacking the PDZ-motif, directly interacts with PDZK1. Colocalization of URAT1 and PDZK1 was observed at the apical membrane of renal proximal tubular cells. The association of URAT1 with PDZK1 enhanced urate transport activities in HEK293 cells (1.4-fold), and the deletion of the URAT1 C-terminal PDZ motif abolished this effect. The augmentation of the transport activity was accompanied by a significant increase in the V(max) of urate transport via URAT1 and was associated with the increased surface expression level of URAT1 protein from HEK293 cells stably expressing URAT1 transfected with PDZK1. Taken together, the present study indicates the novel role of PDZK1 in regulating the functional activity of URAT1-mediated urate transport in the apical membrane of renal proximal tubules.     

X-ray structure of prephenate dehydratase from Streptococcus mutans

Prephenate dehydratase is a key enzyme of the biosynthesis of L-phenylalanine in the organisms that utilize shikimate pathway. Since this enzymatic pathway does not exist in mammals, prephenate dehydratase can provide a new drug targets for antibiotics or herbicide. Prephenate dehydratase is an allosteric enzyme regulated by its end product. The enzyme composed of two domains, catalytic PDT domain located near the N-terminal and regulatory ACT domain located near the C-terminal. The allosteric enzyme is suggested to have two different conformations. When the regulatory molecule, phenylalanine, is not bound to its ACT domain, the catalytic site of PDT domain maintain open (active) state conformation as Sa-PDT structure. And the open state of its catalytic site become closed (allosterically inhibited) state if the regulatory molecule is bound to its ACT domain as Ct-PDT structure. However, the X-ray structure of prephenate dehydratase from Streptococcus mutans (Sm-PDT) shows that the catalytic site of Sm-PDT has closed state conformation without phenylalanine molecule bound to its regulatory site. The structure suggests a possibility that the binding of phenylalanine in its regulatory site may not be the only prerequisite for the closed state conformation of Sm-PDT.     

Purification of catalytically active caspase-12 and its biochemical characterization

Caspase-12, mainly detected in endoplasmic reticulum (ER), has been suggested to play a role in ER-mediated apoptosis and inflammatory caspase activation pathway. Cleavage of the prodomain by caspase-3/-7 at the carboxyl terminus of Asp94 or m-calpain at the carboxyl terminus of Lys158 was reported to be a part of caspase-12-involved apoptosis. We biochemically characterized the prodomain-free forms of caspase-12 and the equivalent enzymes; Δpro1(G95-D419), rev-Δpro1[(T319-N419)-(G95-D318), a reverse form of Δpro1] and rev-Δpro2[(T319-N419)-(T159-D318)]. The three variants showed comparable activities which were dependent on salt concentration and pH. Auto-proteolytic cleavage was observed at two sites (carboxyl termini of Asp318 and Asp320) in Δpro1. Constitutively active forms of caspase-12 (rev-Δpro1 and rev-Δpro2) could induce cell death in cells transfected with the corresponding expression vectors, but no cleavage of caspase-3, DFF45 or Bid was observed, indicating caspase-12 may mediate a distinct apoptotic pathway rather than caspase-8 or -9-mediated cell death.     

Heat shock augments myosin phosphatase target-subunit phosphorylation

Our previous study demonstrated that heat shock augmented vascular contraction. In the present study, we hypothesized that heat shock augments myosin phosphatase target-subunit (MYPT1) phosphorylation resulting in augmented vascular contraction. Endothelium-denuded rat aortic rings were mounted in organ baths, exposed to heat shock (42 degrees C for 45 min), and subjected to contraction 4 h after the heat shock followed by Western blot analysis for MLC(20) (the 20 kDa light chains of myosin II) or MYPT1. The contractile responses in both control and heat shock-treated aorta were inhibited by Y27632, an inhibitor of Rho-kinase. The level of the MLC(20) and MYPT1(Thr855) phosphorylation in response to KCl was higher in heat shock-treated aorta than that in timed-control. The increased MYPT1(Thr855) phosphorylation was inhibited by Y27632 (1.0 microM) in parallel with inhibition of MLC(20) phosphorylation and vascular contraction. These results indicate that heat shock augments MYPT1 phosphorylation resulting in augmented vascular contraction.     

Expression of recombinant epidermal growth factor inE. coli

Epidermal growth factor (EGF) known as a urgastrone is a powerful mitogen with a wide variety of possibilities for medical usages. A mature EGF coding region was isolated from human prepro-EGF sequence by a conventional PCR and cloned into pQE vector in which the gene product was supposed to be expressed with 6×His tag for the subsequent purification. The recombinant mature EGF was expressed in M15[Rep4], anEscherichia coli host strain, in amount of 30–40% of total proteins present inE. coli extract by the addition of isopropylthio-β-galactopyranoside (IPTG). The recombinant EGF purified using a Ni²⁺-NTA affinity column chromatography was active in its ability to induce phosphorylation on tyrosine residues of several substrate proteins when murine NIH3T3 and human MRC-5 fibroblast cells were stimulated with it. This work may provide the basic technology and information for the production of recombinant EGF.