The mitotic checkpoint gene, SIL is regulated by E2F1

Abstract

The SIL gene expression is increased in multiple cancers and correlates with the expression of mitotic spindle checkpoint genes and with increased metastatic potential. SIL regulates mitotic entry, organization of the mitotic spindle and cell survival. The E2F transcription factors regulate cell cycle progression by controlling the expression of genes mediating the G1/S transition. More recently, E2F has been shown to regulate mitotic spindle checkpoint genes as well. As SIL expression correlates with mitotic checkpoint genes, we hypothesized that SIL is regulated by E2F. We mined raw data of published experiments and performed new experiments by modification of E2F expression in cell lines, reporter assays and chromatin immunoprecipitation. Ectopic expression or endogenous activation of E2F induced the expression of SIL, while knockdown of E2F by shRNA, downregulated SIL expression. E2F activated SIL promoter by reporter assay and bound to SIL promoter in vivo. Taken together these data demonstrate that SIL is regulated by E2F. As SIL is essential for mitotic entry, E2F may regulate G2/M transition through the induction of SIL. Furthermore, as silencing of SIL cause apoptosis in cancer cells, these finding may have therapeutic relevance in tumors with constitutive activation of E2F. Published 2008 Wiley-Liss, Inc. This article is a U.S. Government work, and, as such, is in the public domain in the United States of America. Key words: SIL; E2F; mitosisThe SIL gene (SCL Interrupting Locus), located on chromosome 1, encodes a cytosolic protein that has a critical role in cell growth and proliferation.1-3 SIL is tightly regulated during the cell cycle. SIL mRNA expression is higher in rapidly proliferating cells, 4 and it decreases rapidly during terminal differentiation. 5The SIL protein is phosphorylated upon transition into mitosis and is degraded upon exit from mitosis. 4,6 SIL is necessary for mitotic entry and proper organization of the mitotic spindle. 3,7 SIL's critical role in cell growth and proliferation led us to examine its role in tumorigenesis. Increased expression of SIL is observed in multiple types of cancer and is associated with metastatic spread.8 SIL is essential for cancer cells survival as knockdown of SIL resulted in marked delay in mitotic entry coupled with apoptosis, in vitro and in vivo.3 SIL expression in tumors correlates significantly with the expression pattern of the mitotic spindle checkpoint genes and with high histopathological mitotic index. We were interested in elucidating the transcriptional basis for the coregulation of SIL with the expression of other mitotic spindle checkpoint genes.Numerous studies have shown the E2F family of proteins to be aberrantly activated in multiple cancers. The E2F transcription factors have been demonstrated to control gene expression necessary for cell cycle progression, particularly for the G1/S transition. Recently, a role for E2F in regulating mitosis has emerged. 9,10 Specifically, E2F1 was shown to induce the transcription of genes coding...

Cell-cycle-regulated expression of STIL controls centriole number in human cells

“…Interestingly, most of the genes identified to date that cause this disease code for centrosomal proteins (Thornton and Woods, 2009). Finally, it is intriguing that STIL expression is regulated by the transcription factor E2F (Erez et al, 2008), which has previously been shown to be important for the induction of centriole duplication in somatic cells (Meraldi et al, 1999). Thus, as a target of E2F, STIL might represent an important element in the coupling of centriole duplication to cell cycle cues.…”

AMP-Activated Protein Kinase Phosphorylates Retinoblastoma Protein to Control Mammalian Brain Development

“…It is important to note that functional Rb is required specifically for the S and G2 phases in mouse embryonic stem cells (Fluckiger et al, 2006). Furthermore, a number of E2F1 target genes like Mad2 (Sotillo et al, 2007) and SIL (Erez et al, 2008) control the spindle check point during mitosis. Functional complexes containing E2F and Rb are essential for repressing expression of these critical mitotic regulators to maintain the G2M check point (Polager and Ginsberg, 2003).…”

The centrosome duplication cycle in health and disease

“…Furthermore, co‐localization of STIL and SAS‐6 at the proximal ends of nascent centrioles suggested that the two proteins cooperate in cartwheel formation, and interactions between STIL and CPAP/hSAS‐4 have also been revealed [80–83]. Finally, STIL has been identified as a target gene for E2F transcription factors [84], suggesting that STIL may represent an important element in the regulation of the centriole duplication cycle by the Retinoblastoma (pRb) pathway [85].…”