Abstract B182: Nuclear sequestration of ErbB4 receptor tyrosine kinase by PIAS3.

Abstract Background: ErbB4 is a member of EGFR/ErbB family of receptor tyrosine kinases (RTK). ErbB4 is subjected to regulated intramembrane proteolysis (RIP), resulting in the release of a soluble ErbB4 intracellular domain (ICD) into the cytosol. ErbB4 ICD can translocate to the nucleus and function as a transcriptional coregulator. Although nuclear ErbB4 immunoreactivity is frequently observed in breast cancer sections and has been associated with poor clinical outcome compared to membranous or cytosolic ErbB4, little is known how the subcellular localization and functions of ErbB4 ICD are regulated. Results: In search of regulatory mechanisms of ErbB4 ICD localization and function, we identified protein inhibitor of activated STAT3 (PIAS3) as a novel interaction partner of ErbB4 ICD. According to the small ubiquitin-related modifier (SUMO) E3 ligase function of PIAS3, we showed that ErbB4 ICD is post-translationally modified by SUMO-1, and that PIAS3 stimulates SUMOylation of ErbB4 ICD. Upon overexpression of PIAS3, ErbB4 ICD generated from the full-length receptor accumulated into the nucleus and colocalized with PIAS3 and SUMO-1 in promyelocytic leukemia (PML) nuclear bodies, nuclear domains involved in regulation of transcription. Accordingly, PIAS3 overexpression had repressive effects on the transcriptional coregulatory activity of ErbB4. Finally, knockdown of PIAS3 with siRNA decreased nuclear ErbB4, and partially rescued the inhibitory effect of ErbB4 ICD on differentiation of MDA-MB-468 breast cancer and HC11 mammary epithelial cells. Conclusions: We demonstrate that PIAS3 regulates the nuclear sequestration and functions of ErbB4 RTK. Our findings indicate the importance of subcellular distribution of ErbB4 ICD in determining the outcome of ErbB4 signaling in normal and malignant breast cell lines. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr B182.