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Differential Enhancement of Breast Cancer Cell Motility and Metastasis by Helical and Kinase Domain Mutations of Class IA Phosphoinositide 3-Kinase

Departments of ¹ Molecular Pharmacology, ² Anatomy and Structural Biology, and ³ Biochemistry, Albert Einstein College of Medicine, Bronx, New York and ⁴ Department of Biology, Yeshiva University, New York, New York

Requests for reprints: Jonathan M. Backer, Department of Molecular Pharmacology, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461. Phone: 718-430-2153; Fax: 718-430-3749; E-mail: backer{at}aecom.yu.edu.

Class IA (p85/p110) phosphoinositide 3-kinases play a major role in regulating cell growth, survival, and motility. Activating mutations in the p110 isoform of the class IA catalytic subunit (PIK3CA) are commonly found in human cancers. These mutations lead to increased proliferation and transformation in cultured cells, but their effects on cell motility and tumor metastasis have not been evaluated. We used lentiviral-mediated gene transfer and knockdown to produce stable MDA-MB-231 cells in which the endogenous human p110 is replaced with either wild-type bovine p110 or the two most common activating p110 mutants, the helical domain mutant E545K and the kinase domain mutant H1047R. The phosphoinositide 3-kinase/Akt pathway was hyperactivated in cells expressing physiologic levels of helical or kinase domain mutants. Cells expressing either mutant showed increased motility in vitro, but only cells expressing the helical domain mutant showed increased directionality in a chemotaxis assay. In severe combined immunodeficient mice, xenograft tumors expressing either mutant showed increased rates of tumor growth compared with tumors expressing wild-type p110. However, tumors expressing the p110 helical domain mutant showed a marked increase in both tumor cell intravasation into the blood and tumor cell extravasation into the lung after tail vein injection compared with tumors expressing wild-type p110 or the kinase domain mutant. Our observations suggest that, when compared with kinase domain mutations in a genetically identical background, expression of helical domain mutants of p110 produce a more severe metastatic phenotype. [Cancer Res 2009;69(23):8868–76]

Key Words: metastasis • PI3K • PIK3CA