Overexpression of transcription factor Sp1 leads to gene expression perturbations and cell cycle inhibition

• Published in: PloS one Vol. 4; no. 9; p. e7035
• Main Authors: Deniaud, Emmanuelle, Baguet, Joël, Chalard, Roxane, Blanquier, Bariza, Brinza, Lilia, Meunier, Julien, Michallet, Marie-Cécile, Laugraud, Aurélie, Ah-Soon, Claudette, Wierinckx, Anne, Castellazzi, Marc, Lachuer, Joël, Gautier, Christian, Marvel, Jacqueline, Leverrier, Yann
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 15-09-2009; Public Library of Science (PLoS)
• Subjects: Angiogenesis; Animals; Antigens; Apoptosis; Base Sequence; Binding sites; Cancer; Cell Biology/Cell Growth and Division; Cell Biology/Cellular Death and Stress Responses; Cell Biology/Gene Expression; Cell Cycle; Cell death; Cell differentiation; Cell growth; Cell Line, Transformed; Cell Proliferation; Cell Transformation, Neoplastic; Cyclin D2; Cyclin-dependent kinases; Cytoplasm - metabolism; Deoxyribonucleic acid; Deregulation; DNA; DNA fingerprinting; Drosophila; Enrichment; Feedback loops; G1 phase; Gastric cancer; Gene expression; Gene Expression Regulation; Genes; Genetic aspects; Genetic transformation; Genomes; Genomics; Inhibition; Insects; Kinases; Life Sciences; Metastasis; Mice; Models, Biological; Molecular Sequence Data; Negative feedback; Oligonucleotide Array Sequence Analysis; Promoter Regions, Genetic; Promoters; Proteins; Sp1 protein; Sp1 Transcription Factor - metabolism; Stomach cancer; Transcription factors; Transformation; Trends; Tumors; France
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0007035

The ubiquitous transcription factor Sp1 regulates the expression of a vast number of genes involved in many cellular functions ranging from differentiation to proliferation and apoptosis. Sp1 expression levels show a dramatic increase during transformation and this could play a critical role for tumour development or maintenance. Although Sp1 deregulation might be beneficial for tumour cells, its overexpression induces apoptosis of untransformed cells. Here we further characterised the functional and transcriptional responses of untransformed cells following Sp1 overexpression.
We made use of wild-type and DNA-binding-deficient Sp1 to demonstrate that the induction of apoptosis by Sp1 is dependent on its capacity to bind DNA. Genome-wide expression profiling identified genes involved in cancer, cell death and cell cycle as being enriched among differentially expressed genes following Sp1 overexpression. In silico search to determine the presence of Sp1 binding sites in the promoter region of modulated genes was conducted. Genes that contained Sp1 binding sites in their promoters were enriched among down-regulated genes. The endogenous sp1 gene is one of the most down-regulated suggesting a negative feedback loop induced by overexpressed Sp1. In contrast, genes containing Sp1 binding sites in their promoters were not enriched among up-regulated genes. These results suggest that the transcriptional response involves both direct Sp1-driven transcription and indirect mechanisms. Finally, we show that Sp1 overexpression led to a modified expression of G1/S transition regulatory genes such as the down-regulation of cyclin D2 and the up-regulation of cyclin G2 and cdkn2c/p18 expression. The biological significance of these modifications was confirmed by showing that the cells accumulated in the G1 phase of the cell cycle before the onset of apoptosis.
This study shows that the binding to DNA of overexpressed Sp1 induces an inhibition of cell cycle progression that precedes apoptosis and a transcriptional response targeting genes containing Sp1 binding sites in their promoter or not suggesting both direct Sp1-driven transcription and indirect mechanisms.