New Isoform of the TLE3 Gene Encodes a Truncated Protein and is Up-Regulated in Prostate Tumors
Baldini, M.L.; Nakaya, H.I.; Reis, E.M.; Verjovski-Almeida, S.
Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, São Paulo, Brasil
The human TLE (transducin-like Enhancer of split) proteins belong to the Gro/TLE family, which is a family of corepressors. As corepressors they do not bind to DNA directly, but rather are recruited to the template by DNA-bound repressor proteins. The proteins of this family share a primary structure that includes two highly conserved domains, a carboxyl-terminal WD-repeat domain and an amino-terminal Q-rich domain. Recent studies showed that the WD-40 domain in TLE proteins contribute to the interaction with Runt-related transcription factors, AML1 and AML3 and the Q-rich domain is responsible for homotetramerization of the protein.
Recent studies performed by our group revealed an additional exon in the TLE3 gene verified by PCR and sequencing experiments. Moreover, statistical analysis of microarray experiments showed that expression of this novel exon is up-regulated in prostate tumors of high Gleason score, which is associated to patients with a poor clinical prognosis (Reis et al. Oncogene 23: 6684-6692, 2004). Northern blot showed a 5.5 kbp band, which is compatible with a full length alternatively spliced transcript containing the additional exon. This additional exon introduces an early stop codon that truncates TLE carboxyl-terminal WD-40 domain and preserves its amino-terminal Q-rich domain. Sequence similarity searches with mRNAs deposited at GenBank showed that this truncated TLE3 transcript is transcribed in most metazoans. Conceivably, a truncated TLE3 protein may negatively regulate full-length TLE proteins, perhaps by sequestering them in non-productive complexes.
RACE (rapid amplification of cDNA ends) experiments using specific primers confirmed the existence of an additional exon for other members of the TLE gene family (TLE1 and TLE2), indicating that similar isoforms to the TLE3 truncated protein must be common within this protein family. Moreover, real-time PCR experiments using cDNA from 7 normal and tumor prostate tissues confirmed that the alternatively spliced TLE3 form that codes for the truncated protein was up-regulated in most of tumor samples when compared with their normal pair. These results suggest that TLE3 could be a useful molecular marker for prostate cancer.
Supported by FAPESP and CNPq.
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