Ku proteins interact with activator protein-2 transcription factors and contribute to ERBB2overexpression in breast cancer cell lines

Abstract

IntroductionActivator protein-2 (AP-2) α and AP-2γ transcription factors contribute to ERBB2 gene overexpression in breast cancer. In order to understand the mechanism by which the ERBB2 gene is overexpressed we searched for novel AP-2 interacting factors that contribute to its activity.MethodsKu proteins were identified as AP-2α interacting proteins by glutathione serine transferase (GST)-pull down followed by mass spectrometry. Transfection of the cells with siRNA, expression vectors and reporter vectors as well as chromatin immunoprecipitation (ChIP) assay were used to ascertain the implication of Ku proteins on ERBB2 expression.ResultsNuclear proteins from BT-474 cells overexpressing AP-2α and AP-2γ were incubated with GST-AP2 or GST coated beads. Among the proteins retained specifically on GST-AP2 coated beads Ku70 and Ku80 proteins were identified by mass spectrometry. The contribution of Ku proteins to ERBB2 gene expression in BT-474 and SKBR3 cell lines was investigated by downregulating Ku proteins through the use of specific siRNAs. Depletion of Ku proteins led to downregulation of ERBB2 mRNA and protein levels. Furthermore, reduction of Ku80 in HCT116 cell line decreased the AP-2α activity on a reporter vector containing an AP-2 binding site linked to the ERBB2 core promoter, and transfection of Ku80 increased the activity of AP-2α on this promoter. Ku siRNAs also inhibited the activity of this reporter vector in BT-474 and SKBR3 cell lines and the activity of the ERBB2 promoter was further reduced by combining Ku siRNAs with AP-2α and AP-2γ siRNAs. ChIP experiments with chromatin extracted from wild type or AP-2α and AP-2γ or Ku70 siRNA transfected BT-474 cells demonstrated Ku70 recruitment to the ERBB2 proximal promoter in association with AP-2α and AP-2γ. Moreover, Ku70 siRNA like AP-2 siRNAs, greatly reduced PolII recruitment to the ERBB2 proximal promoter.ConclusionsKu proteins in interaction with AP-2 (α and γ) contribute to increased ERBB2 mRNA and protein levels in breast cancer cells.

Targeting Abnormal DNA Repair in Therapy-Resistant Breast Cancers

“…It is possible that increased levels of DSBs resulting from reduced Ku levels may increase expression of ALT NHEJ factors via DNA damage response signaling pathways (37). Alternatively, Ku may transcriptionally regulate genes encoding ALT NHEJ proteins (38–40). …”

Regulation of epithelial cell polarity by PAR-3 depends on Girdin transcription and Girdin–Gαi3 signaling

“…It has been previously reported that PAR-3 occasionally localizes to the nucleus, as well as to cell-cell contacts (Fang et al, 2007). Biochemical studies indicated that PAR-3 can form a complex with the Ku80, Ku70 and catalytic subunits of DNA-dependent protein kinase (DNA-PK), which are also AP-2-binding proteins (Fang et al, 2007;Nolens et al, 2009;Traweger et al, 2008). Thus, PAR-3 might activate Girdin transcription by binding to the DNA-PK-AP-2 complex, and aPKC might be involved in processes such as protein assembly.…”

The DNA repair complex Ku70/86 modulates Apaf1 expression upon DNA damage

“…22 On the other hand, there are several reports indicating that Ku acts as a transcription factor: for example, in the repression of the human a-myosin heavy-chain promoter during heart failure; 23 or in contributing the oncogene ERBB2 overexpression in breast cancer cells by interacting with activator protein-2 transcription factors. 24 In this report we analyse the transcriptional regulation of murine Apaf1 and we demonstrate a functional interaction between Ku70/86 heterodimer and a specific region of Apaf1 promoter. We find that Ku acts as transcription repressor, leading to a downregulation of Apaf1 expression.…”