Year: 2005
Type: dissertation
Abstract: Whether a cell enters the cell cycle, undergoes apoptosis or survives is a consequence of the integration of several cellular and environmental signals. Growth factors, cell contact, and apoptotic inductors regulate a complex system of signal transduction pathways that trigger the activation of a large number of genes. One of the key proteins in the regulation of the cell cycle and the commitment to apoptosis is the transcription factor E2F1. It has been suggested that E2F1 activity levels could determine whether a cell enters the cell cycle, cell-cycle arrest or apoptosis. In these decisions, not only is transcriptional activity important, but also the synchronization of E2F1 activity with specific signal transduction pathways. In this context it has been suggested that activation of the PI 3-kinase pathway inhibits the apoptotic effect of E2F1 overexpression. Since GSK3-beta is a downstream effector of PI 3-kinase, we performed phosphorylation and binding analyses to examine the possible relationship between GSK3-beta and E2F1. The results obtained in this thesis demonstrate that GSK3-beta phosphorylates human E2F1 in vitro at serine 403 and threonine 433. In earlier studies it has already been shown that these two residues are also phosphorylated by the TFIIH kinase, cdk7. We did not detect phosphorylation by GSK3-beta in vivo. However, immunoprecipitation experiments revealed in vivo binding of these proteins. By transient transfection experiments with GSK3-beta and E2F1 constructs, GSK3-beta -RNAi assays, and the use of PI 3-kinase and GSK3-beta specific inhibitors, we demonstrate that GSK3-beta regulates E2F1 transcriptional activity through its interaction with E2F1 transactivation domain and that GSK3-beta kinase activity is not required for this regulation. Our data obtained here integrates into a model in which translocation of GSK3-beta to the nucleus modulates E2F1 activity and, as a consequence, determines whether a cell enters the cell cycle or undergoes apoptosis.
Author: Gisela Garcia Alvarez
Language: English
Subfield: Oncology
Field: Medicine
Domain: Health Sciences
Open Access status: green
OpenAlex ID: W1521542349