FoxO3a Inhibits Tamoxifen-Resistant Breast Cancer Progression by Inducing Integrin α5 Expression

Area of Science:

• Oncology
• Molecular Biology
• Genetics

Background:

• Endocrine therapy resistance is a significant hurdle in treating estrogen receptor α-positive (ERα+) breast cancer (BC).
• The transcription factor Forkhead box class O (FoxO)3a is implicated in tumor progression and is often downregulated in tamoxifen-resistant (TamR) BC cells.

Purpose of the Study:

• To investigate the role of FoxO3a in tamoxifen-resistant ERα+ breast cancer.
• To elucidate the molecular mechanisms by which FoxO3a influences BC cell behavior and aggressiveness.

Main Methods:

• Utilized tamoxifen-resistant (TamR) and sensitive BC cell lines.
• Employed wound-healing, transmigration, and matrigel invasion assays to assess cell motility and invasiveness.
• Conducted qRT-PCR and Western blot analyses for gene and protein expression.
• Performed promoter binding assays (cloning, luciferase, ChIP) to identify FoxO3a binding sites.
• Used siRNA to silence integrin α5 expression.
• Analyzed large-scale gene expression datasets from BC patients.

Main Results:

• Re-expression of FoxO3a in TamR cells significantly reduced their motility and invasiveness.
• FoxO3a induced the expression of integrin α5, a component of the α5β1 fibronectin receptor, at both mRNA and protein levels.
• FoxO3a directly binds to the integrin α5 promoter, regulating its transcription.
• Silencing integrin α5 abolished the inhibitory effects of FoxO3a on migration and invasion.
• A positive correlation between FoxO3a and integrin α5 expression was observed in ERα+ BC patients.

Conclusions:

• The oncosuppressor FoxO3a, through its novel transcriptional target integrin α5, can revert the aggressive phenotype of endocrine-resistant ERα+ breast cancer.
• Targeting the FoxO3a-integrin α5 pathway may represent a promising therapeutic strategy for overcoming endocrine resistance in breast cancer.