ALTERED SHAPE AND CELL-CYCLE CHARACTERISTICS OF FIBROBLASTS EXPRESSING THE E2F1 TRANSCRIPTION FACTOR

To gain an understanding of the role the E2F1 transcription factor pla ys in cell physiology, the full length protein (E2F1) and an amino ter minal deletion of 87 amino acids (E2F1d87) were constitutively express ed in NIH3T3 fibroblasts. Multiple cell lines were generated for each construct. These cells do not proliferate in media containing low seru m and do not proliferate in soft agar, indicating that they are likely not transformed. However, both sets of cell lines show increased DNA synthesis and increased numbers of cells in S phase when cultured in m edia containing low serum, compared to the control cell lines. Cells e xpressing E2F1d87 (but not E2F1) have an extremely rounded morphology when cultured in 10% serum-containing media. These rounded cells lack detectable microfilaments, microtubules, and focal contacts. However, when these cells are cultured in low serum-containing media (0.5%), th ey attain the flattened morphology and cytoskeletal structure of norma l NIH3T3 cells.