Regulation of thymidylate synthase in human colon cancer cells treated with 5-fluorouracil and interferon-gamma.
The effects of fluorouracil (5-FU) and interferon-gamma (IFN-gamma) on the regulation of thymidylate synthase (TS) gene expression were investigated in the human colon cancer H630 cell line. By Western immunoblot analysis, TS protein levels in H630 cells were increased 3-, 5.5-, 5-, and 2.5-fold after 8-, 16-, 24-, and 36-hr exposure to 1 microM 5-FU, respectively. When H630 cells were exposed to varying concentrations of 5-FU (0.3-10 microM) for 24 hr, increases in TS protein up to 5.5-fold were observed. A 24-hr exposure to 1 microM 5-FU resulted in a 4.5-fold increase in the level of TS protein, whereas in 5-FU/IFN-gamma-treated cells TS protein was increased by only 1.8-fold, compared with control cells. IFN-gamma treatment alone did not affect TS protein levels, relative to control. Northern blot analysis revealed no changes in TS mRNA levels when H630 cells were exposed either to 1 microM 5-FU for 8-36 hr, to varying concentrations of 5-FU (0.3-10 microM) for 24 hr, or to the combination of 5-FU and IFN-gamma. Pulse-labeling studies with [35S]methionine demonstrated a 3.5-fold increase in net synthesis of TS in cells treated with 1 microM 5-FU, whereas the level of newly synthesized TS increased only 1.5-fold in cells treated with 5-FU/IFN-gamma, compared with control cells. Pulse-chase studies revealed that the half-lives of TS protein in control and 5-FU-treated cells were equivalent. These findings demonstrate that the increase in TS protein after 5-FU exposure and the subsequent inhibitory effect of IFN-gamma on TS protein expression are both regulated at the post-transcriptional level.
Chu
E
E
NCI-Navy Medical Oncology Branch, Bethesda, Maryland 20889.
Koeller
D M
DM
Johnston
P G
PG
Zinn
S
S
Allegra
C J
CJ
D003110:Colonic Neoplasms / Q000201:enzymology*; D004357:Drug Synergism; D004790:Enzyme Induction / Q000187:drug effects; D004795:Enzyme Stability / Q000187:drug effects; D005472:Fluorouracil / Q000494:pharmacology*; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D007371:Interferon-gamma / Q000494:pharmacology*; D014176:Protein Biosynthesis / Q000187:drug effects; D012333:RNA, Messenger / Q000187:drug effects; D012334:RNA, Neoplasm / Q000187:drug effects; D013940:Thymidylate Synthase / Q000096:biosynthesis / Q000187:drug effects* / Q000235:genetics; D014407:Tumor Cells, Cultured
D012333:RNA, Messenger; D012334:RNA, Neoplasm; D007371:Interferon-gamma; D013940:Thymidylate Synthase; D005472:Fluorouracil