Methotrexate inhibits proteolysis of dihydrofolate reductase by the N-end rule pathway.
The N-end rule relates the in vivo half-life of a protein to the identity of its N-terminal residue. In eukaryotes, the N-end rule pathway is a ubiquitin-dependent, proteasome-based system that targets and processively degrades proteins bearing certain N-terminal residues. Arg-DHFR, a modified dihydrofolate reductase bearing an N-terminal arginine (destabilizing residue in the N-end rule), is short lived in ATP-supplemented reticulocyte extract. It is shown here that methotrexate, which is a folic acid analog and high affinity ligand of DHFR, inhibits the degradation but not ubiquitination of Arg-DHFR by the N-end rule pathway. The degradation of other N-end rule substrates is not affected by methotrexate. We discuss implications of these results for the mechanism of proteasome-mediated protein degradation.
Johnston
J A
JA
Division of Biology, California Institute of Technology, Pasadena 91125, USA.
Johnson
E S
ES
Waller
P R
PR
Varshavsky
A
A
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D017931:DNA Primers; D006868:Hydrolysis; D008727:Methotrexate / Q000494:pharmacology*; D008969:Molecular Sequence Data; D011817:Rabbits; D013762:Tetrahydrofolate Dehydrogenase / Q000378:metabolism*; D001616:beta-Galactosidase / Q000378:metabolism
D017931:DNA Primers; D013762:Tetrahydrofolate Dehydrogenase; D001616:beta-Galactosidase; D008727:Methotrexate