Epidermal growth factor-mediated T-cell factor/lymphoid enhancer factor transcriptional activity is essential but not sufficient for cell cycle progression in nontransformed mammary epithelial cells.
Because beta-catenin target genes such as cyclin D1 are involved in cell cycle progression, we examined whether beta-catenin has a more pervasive role in normal cell proliferation, even upon stimulation by non-Wnt ligands. Here, we demonstrate that epidermal growth factor (EGF) stimulates T-cell factor/lymphoid enhancer factor (Tcf/Lef) transcriptional activity in nontransformed mammary epithelial cells (MCF-10A) and that its transcriptional activity is essential for EGF-mediated progression through G1/S phase. Thus, expression of dominant-negative Tcf4 blocks EGF-mediated Tcf/Lef transcriptional activity and bromodeoxyuridine uptake. In fact, the importance of EGF-mediated Tcf/Lef transcriptional activity for cell cycle progression may lie further upstream at the G1/S phase transition. We demonstrate that dominant-negative Tcf4 inhibits a reporter of cyclin D1 promoter activity in a dose-dependent manner. Importantly, dominant-negative Tcf4 suppresses EGF-mediated cell cycle activity specifically by thwarting EGF-mediated Tcf/Lef transcriptional activity, not by broader effects on EGF signaling. Thus, although expression of dominant-negative Tcf4 blocks EGF-mediated TOPFLASH activation, it has no effect on either EGF receptor or ERK phosphorylation, further underscoring the fact that Tcf/Lef-mediated transcription is essential for cell cycle progression, even when other pro-mitogenic signals are at normal levels. Yet, despite its essential role, Tcf/Lef transcriptional activity alone is not sufficient for cell cycle progression. Serum also stimulates Tcf/Lef transcriptional activation in MCF-10A cells but is unable to promote DNA synthesis. Taken together, our data support a model wherein EGF promotes Tcf/Lef transcriptional activity, and this signal is essential but not sufficient for cell cycle activity.
Graham
Nicholas A
NA
Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, USA.
Asthagiri
Anand R
AR
D002453:Cell Cycle / Q000502:physiology*; D002460:Cell Line; D003598:Cytoskeletal Proteins / Q000502:physiology*; D004268:DNA-Binding Proteins / Q000502:physiology; D004815:Epidermal Growth Factor / Q000502:physiology*; D005260:Female; D005786:Gene Expression Regulation; D006801:Humans; D042361:Mammary Glands, Human / Q000166:cytology / Q000502:physiology*; D015398:Signal Transduction; D015534:Trans-Activators / Q000502:physiology*; D014157:Transcription Factors / Q000502:physiology*; D015533:Transcriptional Activation; D051176:beta Catenin
C495270:CTNNB1 protein, human; D003598:Cytoskeletal Proteins; D004268:DNA-Binding Proteins; D015534:Trans-Activators; D014157:Transcription Factors; D051176:beta Catenin; D004815:Epidermal Growth Factor