The Transcription Factor YY1 Is a Substrate for Polo-Like Kinase 1 at the G2/M Transition of the Cell Cycle

Abstract

Yin-Yang 1 (YY1) is an essential multifunctional zinc-finger protein. It has been shown over the past two decades to be a critical regulator of a vast array of biological processes, including development, cell proliferation and differentiation, DNA repair, and apoptosis. YY1 exerts its functions primarily as a transcription factor that can activate or repress gene expression, dependent on its spatial and temporal context. YY1 regulates a large number of genes involved in cell cycle transitions, many of which are oncogenes and tumor-suppressor genes. YY1 itself has been classified as an oncogene and was found to be upregulated in many cancer types. Unfortunately, our knowledge of what regulates YY1 is very minimal. Although YY1 has been shown to be a phosphoprotein, no kinase has ever been identified for the phosphorylation of YY1. Polo-like kinase 1 (Plk1) has emerged in the past few years as a major cell cycle regulator, particularly for cell division. Plk1 has been shown to play important roles in the G/M transition into mitosis and for the proper execution of cytokinesis, processes that YY1 has been shown to regulate also. Here, we present evidence that Plk1 directly phosphorylates YY1 in vitro and in vivo at threonine 39 in the activation domain. We show that this phosphorylation is cell cycle regulated and peaks at G2/M. This is the first report identifying a kinase for which YY1 is a substrate.

Dronc caspase exerts a non-apoptotic function to restrain phospho-Numb-induced ectopic neuroblast formation in Drosophila

“…In this study, we present evidence that phosphorylation of Numb at the putative Polo sites primarily affect Numb activity in negatively regulating Notch signaling through promoting the endocytosis of Spdo. Although not all the identified Polo phosphorylation sites in Numb perfectly match the optimal consensus sequence initially defined for Polo (Nakajima et al, 2003), the Polo consensus sequence being defined is evolving (Barr et al, 2004), and specific characterized phosphorylation sites in other Polo substrates actually do not conform to the above consensus sequences (Toyoshima-Morimoto et al, 2001;Casenghi et al, 2003;Jackman et al, 2003;Yamaguchi et al, 2005;Mbefo et al, 2010;Yim and Erikson, 2010;Jang et al, 2011;Rizkallah et al, 2011). A common feature appears to be negatively charged residues surrounding the S/T residues; all five sites identified in Numb have this feature.…”

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

“…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).…”

“…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.…”

“…Purified nontagged YY1 as described previously (50) was first phosphorylated in vitro. One microgram of YY1 was incubated for 90 min at 30°C in 20 l of kinase reaction buffer in the absence or presence of CK2␣.…”

“…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).…”