Opposing Functions of TFII-I Spliced Isoforms in Growth Factor-Induced Gene Expression

SummaryMultifunctional transcription factor TFII-I has two spliced isoforms (Δ and β) in murine fibroblasts. Here we show that these isoforms have distinct subcellular localization and mutually exclusive transcription functions in the context of growth factor signaling. In the absence of signaling, TFII-Iβ is nuclear and recruited to the c-fos promoter in vivo. But upon growth factor stimulation, the promoter recruitment is abolished and it is exported out of the nucleus. Moreover, isoform-specific silencing of TFII-Iβ results in transcriptional activation of the c-fos gene. In contrast, TFII-IΔ is largely cytoplasmic in the resting state but translocates to the nucleus upon growth factor signaling, undergoes signal-induced recruitment to the same site on the c-fos promoter, and activates the gene. Importantly, activated TFII-IΔ interacts with Erk1/2 (MAPK) kinase in the cell cytoplasm and imports the Erk1/2 to the nucleus, thereby transducing growth factor signaling. Our results identify a unique growth factor signaling pathway controlled by opposing activities of two TFII-I spliced isoforms.