Integrative molecular and functional profiling of ERBB2-amplified breast cancers identifies new genetic dependencies

Abstract

H Horlings3, F Reyal3, M van der Vijver3, N Turner1, JS Reis-Filho1, CJ Lord1 and A Ashworth1Overexpression of the receptor tyrosine kinase ERBB2 (also known as HER2) occurs in around 15% of breast cancers and is driven by amplification of the ERBB2 gene. ERBB2 amplification is a marker of poor prognosis, and although anti-ERBB2-targeted therapies have shown significant clinical benefit, de novo and acquired resistance remains an important problem. Genomic profiling has demonstrated that ERBB2þve breast cancers are distinguished from ERþve and 'triple-negative' breast cancers by harbouring not only the ERBB2 amplification on 17q12, but also a number of coamplified genes on 17q12 and amplification events on other chromosomes. Some of these genes may have important roles in influencing clinical outcome, and could represent genetic dependencies in ERBB2þve cancers and therefore potential therapeutic targets. Here, we describe an integrated genomic, gene expression and functional analysis to determine whether the genes present within amplicons are critical for the survival of ERBB2þve breast tumour cells. We show that only a fraction of the ERBB2-amplified breast tumour lines are truly addicted to the ERBB2 oncogene at the mRNA level and display a heterogeneous set of additional genetic dependencies. These include an addiction to the transcription factor gene TFAP2C when it is amplified and overexpressed, suggesting that TFAP2C represents a genetic dependency in some ERBB2þve breast cancer cells.

The role of Tcfap2c in tumorigenesis and cancer growth in an activated Neu model of mammary carcinogenesis

“…Knockdown of TFAP2C by siRNA was confirmed by western blot, as seen in Figure 4d. In contrast to earlier reports, 19,21 Neu protein levels were not affected by knockdown of TFAP2C in BT-474 (Figure 4d). Following knockdown of TFAP2C, ERK1/2 activation was significantly reduced (Figure 4d) and was associated with a 46% decrease in cell viability ( P <0.005, Figure 4e).…”

“…17–20 Further, the HER2 breast cancer subtype has been reported to demonstrate dependency on TFAP2C, with knockdown inducing apoptosis. 21 Knockdown of TFAP2C in breast cancer cell lines partially downregulated expression of HER2/ERBB2, though the effects were not uniform for all siRNAs or cell lines. 19,21 Of particular note, the effects on cell survival with knockdown of TFAP2C were not reversed by re-expression of HER2/ERBB2 via a heterologous promoter indicating that TFAP2C regulates the expression of additional genes that mediate cell survival.…”

“…21 Knockdown of TFAP2C in breast cancer cell lines partially downregulated expression of HER2/ERBB2, though the effects were not uniform for all siRNAs or cell lines. 19,21 Of particular note, the effects on cell survival with knockdown of TFAP2C were not reversed by re-expression of HER2/ERBB2 via a heterologous promoter indicating that TFAP2C regulates the expression of additional genes that mediate cell survival. 21 An analysis of clinical specimens has shown that the expression of HER2/ERBB2 demonstrated a significant correlation with TFAP2C expression in primary breast cancer.…”

“…19,21 Of particular note, the effects on cell survival with knockdown of TFAP2C were not reversed by re-expression of HER2/ERBB2 via a heterologous promoter indicating that TFAP2C regulates the expression of additional genes that mediate cell survival. 21 An analysis of clinical specimens has shown that the expression of HER2/ERBB2 demonstrated a significant correlation with TFAP2C expression in primary breast cancer. 22,23 These studies established a central role for TFAP2C in regulating gene expression in the HER2 breast cancer subtype.…”

BIM, PUMA, and the Achilles’ Heel of Oncogene Addiction

“…Indeed, approaches that integrate gene expression and amplifi cation analyses with functional genomics are revealing additional genetic vulnerabilities in HER2 addiction models (39).…”