Comparative genomic analysis reveals a novel mitochondrial isoform of human rTS protein and unusual phylogenetic distribution of the rTS gene.

Background: The rTS gene (ENOSF1), first identified in Homo sapiens as a gene complementary to the thymidylate synthase (TYMS) mRNA, is known to encode two protein isoforms, rTSalpha and rTSbeta. The rTSbeta isoform appears to be an enzyme responsible for the synthesis of signaling molecules involved in the down-regulation of thymidylate synthase, but the exact cellular functions of rTS genes are largely unknown.

Results: Through comparative genomic sequence analysis, we predicted the existence of a novel protein isoform, rTS, which has a 27 residue longer N-terminus by virtue of utilizing an alternative start codon located upstream of the start codon in rTSbeta.

Enhancement of 5-fluorouracil sensitivity by an rTS signaling mimic in H630 colon cancer cells.

The rTSbeta protein has been hypothesized to synthesize signaling molecules that can down-regulate thymidylate synthase. These molecules share biological and chemical properties with acyl-homoserine lactones (AHL), suggesting some AHLs might act as rTS signaling mimics and down-regulate thymidylate synthase. We have determined that the AHL, 3-oxododecanoyl homoserine lactone (3-oxo-C12-(L)-HSL) can down-regulate thymidylate synthase protein at 10 micromol/L and reduce H630 (human colorectal cancer) growth by 50% at 23 micromol/L (IC50) in cell culture.

The rTS signaling pathway as a target for drug development.

The rTS gene was discovered because it codes for a complementary (antisense) RNA to the messenger RNA for thymidylate synthase (TS). It was later shown that rTS also encodes 2 proteins, rTSa and rTSb. Recently, it has become apparent that rTSb overexpression can cause the downregulation of TS protein in a colon cancer cell line through the production of > or = 1 previously unknown signaling molecules.

A novel function for the rTS gene.

The rTS gene codes for a naturally occurring antisense RNA to thymidylate synthase (TS) mRNA and two proteins (rTSalpha and rTSbeta). The role of the major protein product of rTS, rTSbeta has been linked to alterations in TS protein expression, but the precise function of rTSbeta is unknown. In this report we demonstrate that increased expression of rTSbeta is associated with the decrease in TS protein expression due to production of novel, diffusible signal molecules.

Detection of thymidylate synthase modulators by a novel screening assay.

Thymidylate synthase (TS), a key cancer chemotherapeutic target, catalyzes the conversion of deoxyuridylate to thymidylate. TS can serve as a repressor of its own synthesis by binding to its own mRNA through TS-specific binding elements (TBEs). In this report, we describe the use of a luciferase reporter plasmid containing two TBEs that can be used as a tool for the identification and initial profiling of compounds that modulate TS activity, levels, or ability to bind mRNA.

Thymidylate Synthase Gene Expression in Primary Colorectal Cancer and Metastatic Sites.

No Abstract

Natural antisense (rTSalpha) RNA induces site-specific cleavage of thymidylate synthase mRNA.

The 3' untranslated region (UTR) of rTSalpha RNA is complementary (i.e., antisense) to human thymidylate synthase (TS) RNA.