Dihydroorotate Dehydrogenase mRNA and Protein Expression Analysis in Normal and Drug‐Resistant Cells

To follow the expression of the fourth enzyme of pyrimidine de novo synthesis dihydroorotate dehydrogenase (DHODH) in cells and tissues, we studied the DHODH mRNA expression by means of RT‐PCR in rat tissues. Rabbit polyclonal anti‐DHODH immunoglobulins were applied for immunochemical quantification of the enzyme protein by Western blotting. In mouse B‐lymphocytes, which were adapted to tolerate up to a 50‐fold concentration of the DHODH inhibitor leflunomide, a 20 fold protein overexpression was measured. Southern blotting indicated DHODH gene amplification.