Regulation of the Transcription Factor YY1 in Mitosis through Phosphorylation of Its DNA-binding Domain

Abstract

Yin-Yang 1 (YY1) is a ubiquitously expressed zinc finger transcription factor. It regulates a vast array of genes playing critical roles in development, differentiation, and cell cycle. Very little is known about the mechanisms that regulate the functions of YY1. It has long been proposed that YY1 is a phosphoprotein; however, a direct link between phosphorylation and the function of YY1 has never been proven. Investigation of the localization of YY1 during mitosis shows that it is distributed to the cytoplasm during prophase and remains excluded from DNA until early telophase. Immunostaining studies show that YY1 is distributed equally between daughter cells and rapidly associates with decondensing chromosomes in telophase, suggesting a role for YY1 in early marking of active and repressed genes. The exclusion of YY1 from DNA in prometaphase HeLa cells correlated with an increase in the phosphorylation of YY1 and loss of DNA-binding activity that can be reversed by dephosphorylation. We have mapped three phosphorylation sites on YY1 during mitosis and show that phosphorylation of two of these sites can abolish the DNA-binding activity of YY1. These results demonstrate a novel mechanism for the inactivation of YY1 through phosphorylation of its DNA-binding domain. INTRODUCTIONYin-Yang 1 (YY1) is a ubiquitously expressed transcription factor that has been implicated in the regulation of a large number of genes critical for basic processes of development, cell growth, differentiation, cell cycle, and even apoptosis. The essential role of YY1 is underscored by the fact that its deletion resulted in peri-implantation lethality in mice, and disruption of only one allele caused severe developmental abnormalities (Donohoe et al., 1999). A substantial amount of information has been compiled over the past decade about the wide variety of target genes regulated by YY1; however, the regulation of the various functions of YY1 remains enigmatic.The expression of the human yy1 gene is under the control of a promoter that contains three Sp1-binding sites but neither a TATA box nor a CCAAT box, thus classifying YY1 among the constitutively expressed house keeping genes (Yao et al., 1998). Although higher YY1 expression levels have been detected in some types of cancers (Erkeland et al., 2003;Seligson et al., 2005;de Nigris et al., 2006), this type of regulation is not commonly observed for YY1. Other modes of regulation have been proposed including localization, cleavage, interaction with other proteins, and posttranslational modification. Regulation of YY1 through changes in subcellular localization of YY1 into the cytoplasm has been reported during early stages of development in Xenopus (Ficzycz et al., 2001), muscle cell differentiation (Delehouzee et al., 2005), G1/S transition of the mammalian cell cycle (Palko et al., 2004), and apoptosis (Krippner-Heidenreich et al., 2005). YY1 has also been shown to be cleaved under certain conditions of muscle cell differentiation (Walowitz et al., 1998) and apoptosis (Krippner-Heidenr...

Phosphorylation of the Transcription Factor YY1 by CK2α Prevents Cleavage by Caspase 7 during Apoptosis

“…Generation of a YY1 point mutation at position 118 from serine to alanine was performed using the pET-20b(ϩ)-YY1 plasmid and subcloning into PGEX-2T-YY1 (50,51). Mutagenesis was performed using the QuikChange II site-directed mutagenesis kit (Stratagene, La Jolla, CA) according to the manufacturer's instructions.…”

“…YY1 has been shown by others to be a phospho-protein (8,54). More recently, we have been able to map distinct phosphorylation sites in YY1 (50,51). We have identified kinases that phosphorylate YY1 in vitro, and we mapped several phosphorylation sites on YY1 in vivo (50,51).…”

“…More recently, we have been able to map distinct phosphorylation sites in YY1 (50,51). We have identified kinases that phosphorylate YY1 in vitro, and we mapped several phosphorylation sites on YY1 in vivo (50,51). We provide evidence here that one of these kinases is casein kinase 2␣ (CK2␣), a serine/threonine protein kinase that phosphorylates and regulates many cellular substrates involved in cell growth, proliferation, differentiation, and tumorigenesis (2,10,16,17,32,37).…”

ATF7 is stabilized during mitosis in a CDK1-dependent manner and contributes to cyclin D1 expression

“…13,14 CDKs activate or inactivate target proteins by phosphorylation to regulate crucial protein functions in eukaryotic cells. [15][16][17] For instance, entry into mitosis is characterized by phosphorylation of specific transcription factors leading to their displacement from the condensed chromosomes. 15,18,19 In few cases, phosphorylation protects transcription factors from protein degradation during cell cycle progression.…”

“…[15][16][17] For instance, entry into mitosis is characterized by phosphorylation of specific transcription factors leading to their displacement from the condensed chromosomes. 15,18,19 In few cases, phosphorylation protects transcription factors from protein degradation during cell cycle progression. 20,21 In the present study, we show that ATF7 undergoes phosphorylation on its Thr112 residue at the onset of mitosis and is displaced from the condensed chromatin in a CDK-dependent manner.…”