Abstract 4276: Mapping C-terminal transactivation domains of nuclear HER family receptor tyrosine kinases.
Authors: Brand Toni M. , Iida Mari , Wleklinski Matthew J. , Luthar Neha , Starr Megan M. , Wheeler Deric L. 
Published: August 2014

The HER family of receptor tyrosine kinases consist of four receptors, epidermal growth factor receptor (EGFR/ErbB1/HER1), HER2 (ErbB2), HER3 (ErbB3), and HER4 (ErbB4). Collectively, this family of receptors plays a critical role in initiating proliferation and survival signals in several human cancers. It is well established that the HER family receptors rely on two distinct compartments of signaling: 1) Classical membrane bound signaling and 2) nuclear signaling. In the nucleus, HER family receptors can serve as co-transcription factors, mediated by their C-terminal domains, to promote transcription of several genes essential for cell proliferation and cell cycle regulation, including regulation of the gene cyclin D1. However, the domains within the C-terminus of EGFR, HER2 and HER3 that confer this transcriptional potential (transactivation domains) have yet to be defined.

In the current study we aimed to minimally map the regions of the C-terminal domains of EGFR, HER2 and HER3 that function as transactivation domains. We first demonstrate that EGFR, HER2, and HER3 are nuclear localized in their full-length forms in various breast and lung cancer cell lines. Next, we fused various intracellular cytoplasmic domain regions of each receptor to the DNA binding domain of the yeast transcription factor Gal4, and measured the ability for each construct to transactivate Gal4 UAS-luciferase activity. This analysis demonstrated that the C-terminal region distal to the tyrosine kinase domain (CTD) of all HER family receptors have strong transactivation potential, with HER2 exhibiting the highest transactivation potential. Further deletion mapping analysis of each receptor's CTD identified two regions (bipartite) of approximately 25-40 amino acids in length that harbored the majority of the receptors transactivation potential. To understand how the identified bipartite C-terminal regions of each HER family receptor influenced their transcriptional functions we deleted these regions from each full-length receptor and performed cyclin D1 promoter-luciferase assays. While wild type EGFR, HER2, and HER3 overexpression was capable of transactivating cyclin D1-luciferase, bipartite deleted receptors were severely hindered in their ability to regulate the cyclin D1 promoter. Collectively, the findings presented herein suggest that the EGFR, HER2 and HER3 contain a bipartite C-terminal transactivation domain that may be responsible for their ability to function as co-transcription factors.

Citation Format: Toni M. Brand, Mari Iida, Matthew J. Wleklinski, Neha Luthar, Megan M. Starr, Deric L. Wheeler. Mapping C-terminal transactivation domains of nuclear HER family receptor tyrosine kinases. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4276. doi:10.1158/1538-7445.AM2013-4276