A c-Fos- and E1A-interacting component of the tissue factor basal promoter complex mediates synergistic activation of transcription by transforming growth factor-β1

Abstract

Stimulation of quiescent mouse ®broblasts with TGF-b1 and certain other growth factors result in cooperative activation of tissue factor (TF) gene transcription, an event accompanied by the rapid entry of c-Fos into speci®c AP-1 DNA-binding complexes (Felts et al. (1995) Biochemistry 34, 12355 ± 12362). Here, we demonstrate that the ability of TGF-b1 to synergistically activate TF transcription in serum-stimulated ®broblasts is dependent upon both c-Fos and a promoter-speci®c factor with functional properties characteristic of transcriptional coactivators. Inhibition of TF promoter activity by an adenovirus E1A mutant deleted in an essential CREB binding protein (CBP) interaction domain suggests that this factor is distinct from the CBP/p300 family of transcriptional coactivators. Importantly, the ability of this factor to mediate molecular interactions with c-Fos required for transcriptional synergism is directly linked to TGF-b1 signaling. These data suggest a model in which a component of the TF basal transcription complex functions to integrate multiple signaling pathways required for full transcriptional activation of TF in ®broblasts.

The retinoblastoma gene family members pRB and p107 coactivate the AP-1-dependent mouse tissue factor promoter in fibroblasts

“…As shown in Figure 3, wild-type E1A e ectively repressed promoter activity in response to either serum plus TGF-b1 (a) or serum alone (b) when compared to control cells cotransfected with empty expression vector. As previously observed (Felts et al, 1997), mutants de®cient in CBP/p300 binding retained the ability to repress promoter activity under both sets of conditions. These included the deletion mutants d2-36 and d60-80, as well as the point mutant RG2.…”

“…Earlier studies in our laboratory established that the TF gene in mouse ®broblasts is serum-inducible (Felts et al, 1995) and that this e ect can be strongly potentiated by costimulation with transforming growth factor type b1 (Felts et al, 1997). Two AP-1 DNAbinding motifs located between 7200 and 7220, relative to the start site of transcription, were found to be both necessary and su cient for transcriptional activation in response to serum stimulation, or to serum stimulation in the presence of TGF-b1.…”

“…AP1-TF60 consists of the TF AP-1 elements linked to the mouse TF promoter deleted to 760 and containing only the TATA box as a recognizable sequence motif (Felts et al, 1995). Previous work established that the AP-1 elements are both necessary and su cient to confer inducibility in response to serum or synergistic inducibility in response to serum plus TGF-b1 (Felts et al, 1995(Felts et al, , 1997.…”

“…Because the e ect of serum and TGF-b1 was synergistic rather than additive, these observations implied that the AP-1 DNA-binding sites served to integrate components of the serum and TGF-b signaling pathways in a cooperative fashion. A variety of experiments, including the use of ®broblasts derived from c-fos knockout mice, demonstrated that heterodimeric AP-1 DNAbinding complexes speci®cally containing c-Fos were required for transcriptional activation of the TF gene in response to serum and for synergistic activation in response to a combination of serum and TGF-b1 (Felts et al, 1997). However, when c-Fos was overexpressed in stimulated cells, transcriptional synergism was progressively squelched, pointing to the existence of a c-Fos-interacting protein(s) which may function as a speci®c coactivator(s).…”

“…These observations strongly suggested that an E1A-binding protein(s) other than CBP/p300 was required to coactivate cFos-dependent transcription of the TF gene. This factor was provisionally termed CAF for coactivator of Fos (Felts et al, 1997).…”