p210 bcr-abl confers overexpression of inosine monophosphate dehydrogenase: an intrinsic pathway to drug resistance mediated by oncogene.
The p210 bcr-abl fusion protein tyrosine kinase oncogene has been implicated in the pathogenesis of chronic granulocytic leukemia (CGL). Specific intracellular functions performed by p210 bcr-abl have recently been delineated. We considered the possibility that p210 bcr-abl may also regulate the abundance of inosine 5'-monophosphate dehydrogenase (IMPDH) which is a rate-limiting enzyme for de novo guanylate synthesis. We performed studies of the inhibition of IMPDH by tiazofurin, which acts as a competitive inhibitor through its active species that mimics nicotinamide adenine dinucleotide (NAD), i.e. thiazole-4-carboxamide adenine dinucleotide (TAD). The mean inhibitory concentration (IC50) of tiazofurin for cellular proliferation inhibition was 2.3-2.8-fold greater in cells expressing p210 bcr-abl than in their corresponding parent cells proliferating under the influence of growth factors or in growth factor-independent derivative cells not expressing detectable p210 bcr-abl. IMPDH activity was 1.5-2.3-fold greater within cells expressing p210 bcr-abl than in their parent cells. This increase in enzyme activity was a result of 2-fold increased IMPDH protein as determined by immunoblotting. In addition, an increase in the Km value for NAD utilization by IMPDH was observed in p210 bcr-abl transformed cells, but this increase was within the range of resident NAD concentrations observed in the cells. Increased IMPDH protein in p210 bcr-abl transformed cells was traced to an increased level of IMP dehydrogenase II messenger RNA. Thus, regulation of IMPDH gene expression is mediated at least in part by the bcr-abl gene product and may therefore be indicative of a specific mechanism of intrinsic resistance to tiazofurin.
Gharehbaghi
K
K
Laboratory for Experimental Oncology, Indiana University School of Medicine, Indianapolis.
Burgess
G S
GS
Collart
F R
FR
Litz-Jackson
S
S
Huberman
E
E
Jayaram
H N
HN
Boswell
H S
HS
D000818:Animals; D000970:Antineoplastic Agents / Q000633:toxicity; D015152:Blotting, Northern; D002455:Cell Division / Q000187:drug effects; D002461:Cell Line, Transformed; D004261:DNA Replication / Q000187:drug effects; D004351:Drug Resistance / Q000235:genetics*; D016044:Fusion Proteins, bcr-abl / Q000096:biosynthesis / Q000378:metabolism*; D015870:Gene Expression; D007168:IMP Dehydrogenase / Q000096:biosynthesis* / Q000378:metabolism; D051379:Mice; D009857:Oncogenes; D010750:Phosphoproteins / Q000302:isolation & purification / Q000378:metabolism; D019000:Phosphotyrosine; D011061:Poly A / Q000032:analysis / Q000096:biosynthesis; D012313:RNA / Q000032:analysis / Q000096:biosynthesis; D012333:RNA, Messenger; D012254:Ribavirin / Q000031:analogs & derivatives* / Q000633:toxicity; D013936:Thymidine / Q000378:metabolism; D014443:Tyrosine / Q000031:analogs & derivatives / Q000032:analysis
D000970:Antineoplastic Agents; D010750:Phosphoproteins; D012333:RNA, Messenger; D019000:Phosphotyrosine; D011061:Poly A; D014443:Tyrosine; D012254:Ribavirin; D012313:RNA; D007168:IMP Dehydrogenase; D016044:Fusion Proteins, bcr-abl; C033706:tiazofurin; D013936:Thymidine