Species-specific differences in translational regulation of dihydrofolate reductase.
We have observed that rodent cell lines (mouse, hamster) contain approximately 10 times the levels of dihydrofolate reductase as human cell lines, yet the sensitivity to methotrexate (ED(50)), the folate antagonist that targets this enzyme, is similar. Our previous studies showed that dihydrofolate reductase protein levels increased after methotrexate exposure, and we proposed that this increase was due to the relief of feedback inhibition of translation as a consequence of methotrexate binding to dihydrofolate reductase. In the current report, we show that unlike what was observed in human cells, dihydrofolate reductase (DHFR) levels do not increase in hamster cells after methotrexate exposure. We provide evidence to show that although there are differences in the putative mRNA structure between hamster and human mRNA in the dihydrofolate reductase binding region previously identified, "hamsterization" of this region in human dihydrofolate reductase mRNA did not change the level of the enzyme or its induction by methotrexate. Further experiments showed that human dihydrofolate reductase is a promiscuous enzyme and that it is the difference between the hamster and human dihydrofolate reductase protein, rather than the DHFR mRNA, that determines the response to methotrexate exposure. We also present evidence to suggest that the translational up-regulation of dihydrofolate reductase by methotrexate in tumor cells is an adaptive mechanism that decreases sensitivity to this drug.
Hsieh
Yi-Ching
YC
Department of Medicine and Pharmacology, Cancer Institute of New Jersey, Robert Wood Johnson Medical School, University of Medicine and Dentistry of New Jersey, New Brunswick, New Jersey 08903, USA.
Skacel
Nancy E
NE
Bansal
Nitu
N
Scotto
Kathleen W
KW
Banerjee
Debabrata
D
Bertino
Joseph R
JR
Abali
Emine Ercikan
EE
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D015153:Blotting, Western; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D017931:DNA Primers; D015971:Gene Expression Regulation, Enzymologic; D006801:Humans; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009690:Nucleic Acid Conformation; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000737:chemistry / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity; D013762:Tetrahydrofolate Dehydrogenase / Q000737:chemistry / Q000235:genetics*
D017931:DNA Primers; D012333:RNA, Messenger; D013762:Tetrahydrofolate Dehydrogenase