title: Regulation of inosine monophosphate dehydrogenase type I and type II isoforms in human lymphocytes.
abstract: The enzyme inosine monophosphate dehydrogenase (IMPDH) catalyzes the rate-limiting step in the de novo biosynthesis of guanine nucleotides. Inhibition of IMPDH leads to immunosuppression by decreasing guanine nucleotides that are required for the proliferation of lymphocytes. IMPDH activity is mediated by two highly conserved isoforms, type I and type II. We have characterized the mRNA and protein expression of the two isoforms in a variety of human tissues, peripheral blood mononuclear cells (PBMCs), and selected cell lines to investigate their regulation. Type I mRNA was expressed in most tissues with high expression in PBMCs and low expression in thymus. IMPDH type II transcript was also detected in most tissues with low expression in spleen and PBMCs. In PBMCs, induction of both type I and type II mRNAs was observed within 12 hr of mitogenic stimulation. Using type-selective IMPDH antibodies, an increase in the levels of type I and type II proteins was observed after mitogenic stimulation. The effect of two IMPDH inhibitors, MPA and VX-497, was investigated on the expression of type I and type II isoforms. VX-497 is an orally bioavailable, potent and reversible inhibitor of IMPDH, with broad applicability in many viral and immune system-mediated diseases. MPA and VX-497 inhibit both isoforms of IMPDH in vitro. Prolonged treatment of lymphocytes with either VX-497 or MPA did not lead to an increase in type I or type II IMPDH protein levels. These results are discussed in the context of IMPDH being a target for immunosuppressive, anti-viral and anti-cancer therapy.
authors.affiliation: Vertex Pharmaceuticals Inc., 130 Waverly Street, Cambridge, MA 02139, USA. jugnu_jain@vrtx.com
authors.forename: Jugnu
authors.initials: J
authors.lastname: Jain
authors.forename: Susan J
authors.initials: SJ
authors.lastname: Almquist
authors.forename: Pamella J
authors.initials: PJ
authors.lastname: Ford
authors.forename: Dina
authors.initials: D
authors.lastname: Shlyakhter
authors.forename: Yongping
authors.initials: Y
authors.lastname: Wang
authors.forename: Elmar
authors.initials: E
authors.lastname: Nimmesgern
authors.forename: Ursula A
authors.initials: UA
authors.lastname: Germann
mesh_terms: D002219:Carbamates / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D007168:IMP Dehydrogenase / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism*; D007963:Leukocytes, Mononuclear / Q000187:drug effects / Q000201:enzymology; D008214:Lymphocytes / Q000201:enzymology*; D009173:Mycophenolic Acid / Q000494:pharmacology; D010671:Phenylurea Compounds / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D014407:Tumor Cells, Cultured
chemical_list: D002219:Carbamates; D004791:Enzyme Inhibitors; D007527:Isoenzymes; C407002:N-3-(3-(3-methoxy-4-oxazol-5-ylphenyl)ureido)benzylcarbamic acid tetrahydrofuran-3-yl ester; D010671:Phenylurea Compounds; D012333:RNA, Messenger; D007168:IMP Dehydrogenase; D009173:Mycophenolic Acid