Expression of rTSβ as a 5-fluorouracil resistance marker in patients with primary breast cancer

Abstract

Abstract. Expression of thymidylate synthase (TS) in tumor cells is frequently suggested as an important prognostic factor for patients scheduled for chemotherapy with 5-fluorouracil (5-FU). However, clinical evidence does not fully support such an anticipation. We studied the expression of rTSß, a reverse orientation gene of TS, as a 5-FU resistance marker in patients with primary breast cancer. Expression of rTSß was examined in 129 patients with newly diagnosed breast cancer and five breast cancer cell lines by immunohistochemistry, immunocytochemistry and immunoblotting. Clinically, expression of rTSß was found to correlate with survival of the patients (p=0.023) when patients received chemotherapeutic regimen containing 5-FU. In vitro, rTSß expression was found to correlate with 5-FU resistance in breast cancer cell lines. Notably, in the 5-FU-resistant cells, rTSß was identified in the nucleus, whereas in the 5-FUsensitive cells, rTSß was found in the cytoplasm. Nuclear localization of rTSß was further found to be associated with protein farnesylation. Therefore, nuclear expression of rTSß could be a novel 5-FU resistance marker in patients with primary breast cancer. IntroductionBreast cancer is the second most prevalent malignancy and the fourth leading cause of cancer death in Taiwanese women (1). Although the death rate of uterine cervical cancer has decreased significantly in the past two decades due to the improvement in the early detection of the disease by pap smear among women over 35 years of age; for breast cancer, not only has the incidence increased markedly, but also the age of tumor occurrence has decreased dramatically, which is about ten years younger than that of the Western population (2-4).Clinically, depending upon the status of estrogen and/or progesterone receptors in cancer cells, some patients receive non-steroidal anti-estrogen tamoxifen for hormonal therapy (5). However, most of the patients could only choose adjuvant chemotherapy containing 5-fluorouracil (5-FU) after surgery. 5-FU is a pro-drug that is converted to fluorouridine to interfere with RNA synthesis, or to 5-fluoro-2'-deoxyuridine-5'-monophosphate (FdUMP) to inhibit thymidylate synthase (TS) and the consequent DNA synthesis. In the presence of N 5 , 10 -methylene tetrahydrofolate, FdUMP further forms a stable ternary complex with TS to inhibit synthesis of deoxythymidine monophosphate (dTMP) (reviewed in ref. 6). TS expression in tumor cells is considered as a key prognostic factor for patients receiving chemotherapy containing 5-FU (7).However, clinical evidence did not fully support this expectation (6,(8)(9)(10)(11)(12)(13). On the other hand, expression of the rTS (ENOSF1) gene (14-16) was found to be closely associated with 5-FU sensitivity besides nucleotide metabolism-related enzymes, e.g., thymidine phosphorylase, ribonucleotide reductase, uridine phosphorylase and thymidine kinase (17-19) that directly affects pyrimidine synthesis in de novo or salvage pathways (11).The rTS is located with the TS gene on the...

Enzymatic and Structural Characterization of rTSγ Provides Insights into the Function of rTSβ

“…In clinical studies, rTSβ was found to be expressed in breast cancer tissue but not the surrounding tissues. 8 Furthermore, a statistically significant correlation was found between the level of rTSβ expression and a decrease in the five year survival rate of colon cancer patients. 5 The 27 residue longer N-terminus of rTSγ, compared to rTSβ, is proposed to constitute a mitochondrial signaling sequence, 9 suggesting that rTSβ and rTSγ serve similar enzymatic functions.…”

Transient knockdown and overexpression reveal a developmental role for the zebrafish enosf1b gene

“…The same group also reported a statistically significant decrease in five year survival of colon cancer patients with tumor hsENOSF1β expression compared to colon cancer patients without tumor hsENOSF1β expression [ 29 ]. Taken together, in vitro cell culture data [ 23 - 27 ] and human patient data [ 28 , 29 ] suggest a connection between hsENOSF1β expression and cancer.…”

“…In cell culture, hsENOSF1β expression appears to be regulated by environmental factors such as cell density, time in culture, and exposure to chemotherapy drugs that affect thymidylate synthase or folate pathway enzymes [ 23 - 27 ]. Using patient samples from a Taiwanese population, Kuo et al [ 28 ] showed that hsENOSF1β is expressed in breast tumor tissue and not surrounding tissue. The α or γ splice forms were not found in the patient samples [ 28 ].…”

“…Using patient samples from a Taiwanese population, Kuo et al [ 28 ] showed that hsENOSF1β is expressed in breast tumor tissue and not surrounding tissue. The α or γ splice forms were not found in the patient samples [ 28 ]. The same group also reported a statistically significant decrease in five year survival of colon cancer patients with tumor hsENOSF1β expression compared to colon cancer patients without tumor hsENOSF1β expression [ 29 ].…”

Pharmacogenetics and pharmacogenomics of anticancer agents

“…5‐FU undergoes complex anabolic and catabolic biotransformation. Gene products involved in this transformation include dihydropyrimidine dehydrogenase (DPD or DPYD ), which breaks down 5‐FU,84–88 and those drug targets (eg, thymidylate synthase [TS or TYMS ])89, 90 and methylenetetrahydrofolate reductase ( MTHFR ). Several of these genes have been shown to affect 5‐FU treatment outcomes.…”