Differential expression and splicing isoform analysis of human Tcf-4 transcription factor in brain tumors.
Tcf family transcription factors are the downstream effectors of the Wnt signal transduction pathway that regulates developmental and oncogenetic processes among species. The alternative splicing of consecutive exons in the 3' part of the Tcf-4 gene and an error-prone A9 repeat in exon 17 have recently been examined in several tumors. To further understand the roles played by differential expression and splicing isoforms of human Tcf-4 in brain tumorigenesis, the expression of the 3' part of the Tcf-4 gene (exons 10-17) was analyzed by RT-PCR, nested RT-PCR and DNA sequencing. The results showed that at least 13 of the Tcf-4 alternative splicing isoforms were found and most of them were overexpressed in various brain tumors. L3 isoform was particularly dominant in metastasis. Several novel splicing isoforms were identified. One that contains different combinations of exon 16 (10-11-12-16-17, S5) was found in normal brain and pituitary adenoma but not in astrocytoma, meningioma or metastasis, whereas the other that contains part of intron 16, designated exon-16', was found in metastasis. Overall 23% of sequencing analysis in brain tumors exhibited frameshift mutations in an A9 repeat region of exon 17. These mutants exhibited 2-base or 1-base deletion (A7, A8) and 1-base insertion (A10). Nonetheless, in vitro functional assay showed that these mutants did not affect the transactivity of Tcf-4 comparing to wild-type Tcf-4. Collectively, our data suggest that a large number of alternative splicing isoforms may together with variable mutations of A9 repeat region maintain balanced pools of Tcf-4 isoforms during brain tumorigenesis.
Howng
Shen-Long
SL
Department of Neurosurgery, Kaohsiung Medical University, Kaohsiung, Taiwan, ROC.
Huang
Feng-Hsiang
FH
Hwang
Shiuh-Lin
SL
Lieu
Ann-Shuung
AS
Sy
Wei-Di
WD
Wang
Chihuei
C
Hong
Yi-Ren
YR
D000236:Adenoma / Q000235:genetics* / Q000473:pathology*; D001254:Astrocytoma / Q000235:genetics* / Q000473:pathology* / Q000556:secondary; D001932:Brain Neoplasms / Q000235:genetics* / Q000473:pathology* / Q000556:secondary; D004252:DNA Mutational Analysis; D004268:DNA-Binding Proteins / Q000096:biosynthesis*; D005260:Female; D020869:Gene Expression Profiling; D018257:Helix-Loop-Helix Motifs; D006801:Humans; D008297:Male; D010911:Pituitary Neoplasms / Q000235:genetics* / Q000473:pathology*; D020033:Protein Isoforms; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D015398:Signal Transduction; D051820:TCF Transcription Factors; D058118:Transcription Factor 7-Like 2 Protein; D014157:Transcription Factors / Q000096:biosynthesis*
D004268:DNA-Binding Proteins; D020033:Protein Isoforms; D051820:TCF Transcription Factors; C544894:TCF7L2 protein, human; D058118:Transcription Factor 7-Like 2 Protein; D014157:Transcription Factors