Identification of a series of transforming growth factor beta-responsive genes by retrovirus-mediated gene trap screening

Transforming growth factor beta (TGF-beta) plays important roles in the reg ulation of proliferation, differentiation! apoptosis, and carcinogenesis. T o identify genes responsible for maintaining the phenotype induced by TGF-b eta, we performed a retrovirus-mediated gene trap screening designed to iso late TGF-beta-responsive genes in human lung carcinoma cell line A549. Afte r screening 249 trap lines, 21 were found to express the reporter beta-gala ctosidase gene in a TGF-beta-responsive manner. Interestingly, in large pro portions of these trap lines, the reporter gene uas responsive also to phor bol ester and was suppressed by gamma interferon, Fragments of all these tr apped genes were recovered by 5'- and 3'-rapid amplification of cDNA ends ( RACE), and in 15 out of 21 cases (71%), the TGF-beta responsiveness of the endogenous genes H-as confirmed by RNA blot hybridization. In at least five cases, the TGF-beta-induced upregulation was found to be cycloheximide res istant, suggesting the roles of the genes in the TGF-beta-induced primary r esponses. Sequence analyses revealed that 43% (9 of 21) of the trapped gene s were novel and that the remainder included genes previously reported to b e upregulated by TGF-beta, such as epidermal growth factor receptor and bet a 1 integrin, documenting the validity of this approach, Other known genes include the ones encoding the proteins associated with cell proliferation ( ribosomal proteins S15a, hNRP/NAP-1, and lipocortin II), focal adhesions (p axillin), and transcriptional regulation (thyroid hormone receptor activato r molecule 1 [TRAM-1]).