Tissue-specific expression of functional isoforms of mouse folypoly-gamma-glutamae synthetase: a basis for targeting folate antimetabolites.
Folates and folate antimetabolites are metabolically trapped in mammalian cells as polyglutamates, a process catalyzed by folylpoly-gamma-glutamate synthetase (FPGS). Using 5'-rapid amplification of cDNA ends, RNase protection assays, transfection of cDNAs into FPGS-deficient cells, and kinetic analysis of recombinant enzymes expressed in insect cells, it was determined that the species of active FPGS in mouse liver and kidney was different from that in mouse tumor cells, bone marrow, and intestine. The NH2-terminal peptide of hepatic enzyme contained 18 amino acids not found in enzyme from dividing tissues, and the specificity of the two isoforms for antifolates also differed, suggesting different architecture of the active sites. In most tissues, the expression of one isozyme or the other was an all-or-nothing event. The exclusive use of one of two alternative sets of initial coding exons in different tissues underlies this phenomenon, suggesting the design of antifolates specific for activation by individual FPGS isoforms and hence tissue-selective targeting of antifolate therapy for cancer, arthritis, or psoriasis.
Turner
F B
FB
Department of Pharmacology and Toxicology, Medical College of Virginia, Virginia Commonwealth University, Richmond 23298, USA.
Andreassi 2nd
J L
JL
Ferguson
J
J
Titus
S
S
Tse
A
A
Taylor
S M
SM
Moran
R G
RG
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D018076:DNA, Complementary / Q000302:isolation & purification; D005493:Folic Acid Antagonists / Q000378:metabolism; D007527:Isoenzymes / Q000096:biosynthesis* / Q000737:chemistry / Q000235:genetics; D007700:Kinetics; D007939:Leukemia L1210 / Q000201:enzymology; D008099:Liver / Q000201:enzymology*; D051379:Mice; D008969:Molecular Sequence Data; D010453:Peptide Synthases / Q000096:biosynthesis* / Q000737:chemistry / Q000235:genetics; D011994:Recombinant Proteins / Q000378:metabolism; D017421:Sequence Analysis; D012689:Sequence Homology, Nucleic Acid; D013379:Substrate Specificity; D014018:Tissue Distribution; D014407:Tumor Cells, Cultured
D018076:DNA, Complementary; D005493:Folic Acid Antagonists; D007527:Isoenzymes; D011994:Recombinant Proteins; D010453:Peptide Synthases; C023103:folylpolyglutamate synthetase