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Effects of Tiazofurin on Protooncogene Expression during HL-60 Cell Differentiation¹

Laboratory of Clinical Pharmacology, Dana-Farber Cancer Institute and Harvard Medical School, Boston, MA 02115

The synthetic nucleoside analogue, tiazofurin (2-ß-D-ribofuranosylthiazole-4-carboxamide, NSC 286193) is an inhibitor of the enzyme inosine monophosphate (IMP) dehydrogenase and depletes guanine nucleotide pools. In the present study, we have monitored the effects of tiazofurin on human HL-60 promyelocytic cell differentiation and protooncogene expression. Tiazofurin (10 µM) induced a more differentiated HL-60 cell phenotype as determined by histochemical staining and decreased myeloperoxidase gene expression. This induction of differentiation was associated with a loss of proliferative capacity and decreases in clonogenic survival. The results also demonstrate that tiazofurin induces a down-regulation of c-myc mRNA levels. In contrast, there was no detectable change in the level of 3.8-kilobase c-myb transcripts. Furthermore, treatment of HL-60 cells with tiazofurin resulted in the appearance of an additional c-myb mRNA with an apparent size of 3.3 kilobases. The addition of guanosine to tiazofurin-treated HL-60 cells prevented the down-regulation of c-myc transcripts and also inhibited induction of the 3.3-kilobase c-myb transcript. Moreover, this additional transcript was not detected during induction of HL-60 cells by dimethyl sulfoxide, tumor necrosis factor, and retinal, but was induced by another IMP dehydrogenase inhibitor, mycophenolic acid. These results suggest a role for guanosine ribonucleotides in the regulation of c-myc and c-myb gene expression during HL-60 cell differentiation. The results also suggest that changes in c-myb expression can be dissociated from that of c-myc and induction of myeloid differentiation.

¹ This investigation was supported in part by USPHS Grants CA42802 and CA01092, awarded by the National Cancer Institute, DHHS, and by a Burroughs-Wellcome Clinical Pharmacology Scholar Award [D. W. K.].

² To whom requests for reprints should be addressed, at Division of Medicine, Dana-Farber Cancer Institute, 44 Binney Street, Boston, MA 02115.

Received 2/ 1/88. Revised 7/25/88. Accepted 7/29/88.

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