Abstract 488: E2F2-mediated copy number changes drive metastasis and therapeutic response of HER2-positive tumors through Col1a1, CHAD, and AKT-dependent mechanisms
Authors: Rennhack Jonathan P. , Sun Kelian , Honeysett Jordan , Andrechek Eran 
Published: July 2017

Abstract
The E2F family of transcription factors is classically known to regulate G1 to S-phase transition in cell cycle but has emerging roles in HER2+ breast cancer. A loss of E2F1 or E2F2, in a HER2 mouse model, MMTV-Neu, leads to a decrease in tumor metastasis1. It is not known what mechanistic roles specific E2Fs are playing in this process. To investigate this, we leveraged and bioinformatic principles, including genomics and transcriptomics with traditional laboratory science and high throughput drug screening projects. This experimental approach immediately revealed that loss of E2F2 is significantly associated with a more unstable tumor including an increase in copy number alterations, single nucleotide variants, and translocations. Further analysis revealed a conserved copy number alteration in both mouse and humans. Specifically we noted the amplification of 17q21.33 in 25% of HER2+ patients. The analogous region chromosome 11D was lost in 30% of the less metastatic MMTV-Neu E2F2 knockout mice indicating a role of the region in tumor metastasis. Transcriptomic data revealed that two genes, Collagen Type I, alpha 1 (Col1a1) and Chondroadherin (CHAD), were potential genes of significance in the amplification event. CRISPR mediated knockout studies were conducted to determine each gene’s effect on tumor cell migration and metastasis in mouse and human derived cell lines. Wound healing assays and tail vein injection have shown the Col1a1 and CHAD KO cell lines have a delay in cell migration (P&lt;.01) and reduced ability to colonize the lung (P&lt;.05) respectively. Oncogenic signaling data shows that the 17q21.33 amplification event has higher AKT and E2F2 signaling than HER2 positive tumors without the event. It was hypothesized that the tumors would be dependent on the signaling and perturbation of the network might be an effective therapy for patients with the 17q21.33 amplification event. To investigate this we identified deferentially lethal siRNAs and compounds between HER2+ tumors with and without the 17q21.33 event in the Achilles, CCLE, and PDX datasets. A String-DB analysis showed many of the deferentially lethal genes and compounds centered around AKT. A decrease in AKT signaling through siRNA or chemical compound results in the death of the cell in the 17q21.33 amplified samples but not the HER2+ samples without the event. This study reveals that patients’ with a 17q21.33 amplification event have more metastatic tumors mediated through Col1a1 and CHAD and may be responsive to AKT targeting therapy.
References1. Andrechek ER: HER2/Neu tumorigenesis and metastasis is regulated by E2F activator transcription factors. Oncogene 2013.
Citation Format: Jonathan P. Rennhack, Kelian Sun, Jordan Honeysett, Eran Andrechek. E2F2-mediated copy number changes drive metastasis and therapeutic response of HER2-positive tumors through Col1a1, CHAD, and AKT-dependent mechanisms [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 488. doi:10.1158/1538-7445.AM2017-488