An alternative transcript derived from the trio locus encodes a guanosine nucleotide exchange factor with mouse cell-transforming potential.
By screening cDNA expression libraries derived from fresh leukemic cells of adult T-cell leukemia for the potential to transform murine fibroblasts, NIH3T3, we have identified a novel transforming gene, designated Tgat. Expression of Tgat in NIH3T3 resulted in the loss of contact inhibition, increase of saturation density, anchorage-independent growth in a semisolid medium, tumorigenicity in nude mice, and increased invasiveness. Sequence comparison revealed that an alternative RNA splicing of the Trio gene was involved in the generation of Tgat. The Tgat cDNA encoded a protein product consisting of the Rho-guanosine nucleotide exchange factor (GEF) domain of a multifunctional protein, TRIO, and a unique C-terminal 15-amino acid sequence, which were derived from the exons 38-46 of the Trio gene and a novel exon located downstream of its last exon (exon 58), respectively. A Tgat mutant cDNA lacking the C-terminal coding region preserved Rho-GEF activity but lost the transforming potential, indicating an indispensable role of the unique sequence. On the other hand, treatment of Tgat-transformed NIH3T3 cells with Y-27632, a pharmacological inhibitor of Rho-associated kinase, abrogated their transforming phenotypes, suggesting the coinvolvement of Rho-GEF activity. Thus, alternative RNA splicing, resulting in the fusion protein with the Rho-GEF domain and the unique 15 amino acids, is the mechanism generating the novel oncogene, Tgat.
Yoshizuka
Naoto
N
Department of Molecular Microbiology & Immunology, Nagasaki University Graduate School of Biomedical Sciences, 1-12-4 Sakamoto, 852-8523, Japan.
Moriuchi
Ryozo
R
Mori
Tsuyoshi
T
Yamada
Kenji
K
Hasegawa
Sumitaka
S
Maeda
Takahiro
T
Shimada
Takako
T
Yamada
Yasuaki
Y
Kamihira
Shimeru
S
Tomonaga
Masao
M
Katamine
Shigeru
S
D016475:3T3 Cells; D000818:Animals; D002471:Cell Transformation, Neoplastic; D002895:Chromosomes, Human, Pair 5 / Q000235:genetics; D020662:Guanine Nucleotide Exchange Factors / Q000235:genetics*; D006801:Humans; D051379:Mice; D008819:Mice, Nude; D008969:Molecular Sequence Data; D009361:Neoplasm Invasiveness; D009374:Neoplasms, Experimental / Q000473:pathology; D009857:Oncogenes; D010750:Phosphoproteins / Q000235:genetics*; D017346:Protein Serine-Threonine Kinases / Q000235:genetics*; D014158:Transcription, Genetic; D014162:Transfection
D020662:Guanine Nucleotide Exchange Factors; D010750:Phosphoproteins; D017346:Protein Serine-Threonine Kinases; C099628:TRIO protein, human