HER2 Signaling Drives DNA Anabolism and Proliferation through SRC-3 Phosphorylation and E2F1-Regulated Genes

Area of Science:

• Molecular Oncology
• Cancer Cell Signaling
• Breast Cancer Research

Background:

• Human Epidermal growth factor Receptor 2 (HER2) amplification occurs in ~20% of early-stage breast cancers, associated with poor prognosis and endocrine therapy resistance.
• Current HER2-targeted therapies (trastuzumab, lapatinib) improve survival but resistance and metastasis remain challenges.
• Mechanisms of nuclear HER2 signaling, particularly regarding therapeutic resistance and proliferation, are not fully understood.

Purpose of the Study:

• To identify nuclear effectors and gene targets of HER2 transcriptional signaling in human breast cancer.
• To elucidate the role of HER2 signaling in promoting proliferation and therapeutic resistance.
• To investigate potential therapeutic strategies targeting identified signaling nodes.

Main Methods:

• Employed biochemical and bioinformatic approaches to analyze HER2 transcriptional signaling.
• Assessed the impact of HER2 inhibition on Steroid Receptor Coactivator-3 (SRC-3) phosphorylation, activity, and gene recruitment.
• Analyzed gene expression signatures enriched for E2F1 binding sites and correlated with proliferation and DNA replication.

Main Results:

• HER2 inhibition reduced SRC-3 phosphorylation and its recruitment to gene regulatory elements.
• HER2-regulated transcripts are enriched for E2F1 binding sites, defining a proliferative gene signature.
• HER2 signaling drives breast cancer proliferation via E2F1-mediated regulation of DNA metabolism and replication genes, involving SRC-3 activity.
• Targeting the cyclin-dependent kinase (CDK) 4/6 node with palbociclib, in combination with lapatinib, blocks DNA synthesis by disrupting E2F1 signaling.

Conclusions:

• HER2 signaling promotes breast cancer proliferation through nuclear regulation of E2F1 and SRC-3.
• Combined targeting of HER2 (e.g., lapatinib) and CDK4/6 (e.g., palbociclib) effectively inhibits DNA synthesis.
• These findings support the development of novel pharmacologic combinations for adjuvant therapy and overcoming resistance in HER2-driven breast cancers.