Decreased expression of protooncogenes c-fos, c-myc, and c-jun following polyamine depletion in IEC-6 cells.
Direct exposure of small intestinal mucosal cells to luminal polyamines stimulates proliferation. This study tests the hypothesis that the protooncogenes c-fos, c-myc, c-jun, and junB are involved in the mechanism by which polyamines modulate mucosal growth. Studies were conducted in the IEC-6 cell line, derived from rat small intestinal crypt cells. Cells were grown in Dulbecco's minimal essential medium containing 5% dialyzed fetal bovine serum (dFBS) in the presence of absence of alpha-difluoromethylornithine (DFMO), a specific inhibitor of ornithine decarboxylase, which is the rate-limiting enzyme for polyamine synthesis. Cellular polyamine levels, cell growth, and relative abundance of c-fos, c-myc, c-jun, and junB mRNAs, were measured at 1, 2, 4, 6, 8, and 12 days after initial plating. The intracellular polyamines, spermidine and spermine, and their precursor, putrescine, in DFMO-treated cells decreased significantly at 2 days and remained depleted thereafter. Although DFMO profoundly decreased growth and final cell number, both control and DFMO-treated cells entered a plateau phase by 6 days. In control cells, c-myc and c-jun mRNA levels significantly increased on days 4-6 and then returned to a basal level of expression, which was maintained thereafter. c-fos mRNA in quiescent cells after 24 h serum deprivation was significantly stimulated by 5% dFBS, although a steady-state level of c-fos mRNA was undetectable in control cells. Treatment with DFMO not only prevented increased expression of c-myc and c-jun protooncogenes at 4 days, but also significantly reduced steady-state levels of c-myc and c-jun mRNA between 6 and 12 days.(ABSTRACT TRUNCATED AT 250 WORDS)
Wang
J Y
JY
Department of Physiology, University of Tennessee College of Medicine, Memphis 38163.
McCormack
S A
SA
Viar
M J
MJ
Wang
H
H
Tzen
C Y
CY
Scott
R E
RE
Johnson
L R
LR
D000818:Animals; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D000518:Eflornithine / Q000494:pharmacology; D015870:Gene Expression; D007421:Intestine, Small / Q000166:cytology / Q000378:metabolism / Q000502:physiology*; D011073:Polyamines / Q000378:metabolism*; D016760:Proto-Oncogene Proteins c-fos / Q000235:genetics*; D016755:Proto-Oncogene Proteins c-jun / Q000235:genetics*; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics*; D013095:Spermidine / Q000494:pharmacology
D011073:Polyamines; D016760:Proto-Oncogene Proteins c-fos; D016755:Proto-Oncogene Proteins c-jun; D016271:Proto-Oncogene Proteins c-myc; D013095:Spermidine; D000518:Eflornithine