Characterization of a tumor-associated activating mutation of the p110β PI 3-kinase

Area of Science:

• Biochemistry
• Molecular Biology
• Oncology

Background:

• The phosphoinositide 3-kinase (PI3K) pathway is frequently dysregulated in cancer, primarily through mutations in PIK3CA (encoding p110α) or loss of PTEN.
• Activating mutations are rare in other PI3K catalytic subunits, including p110β.

Purpose of the Study:

• To characterize the functional and oncogenic properties of the p110β E633K mutation, identified in a Her2-positive breast cancer.
• To elucidate the mechanism by which this mutation activates p110β and promotes cancer phenotypes.

Main Methods:

• Biochemical assays to measure basal and activated p110β activity.
• Cellular assays to assess Akt and S6K1 activation, transformation, proliferation, survival, and chemotaxis.
• Analysis of protein structure and membrane interaction.

Main Results:

• The p110β E633K mutation significantly increases basal p110β enzymatic activity.
• Expression of the mutant leads to enhanced Akt and S6K1 activation, promoting cell transformation, proliferation, survival, and chemotaxis, particularly under low-serum conditions.
• The mutation enhances p110β membrane association, independent of the Ras-binding domain, suggesting a novel activation mechanism.

Conclusions:

• The E633K mutation represents the first identified activating oncogenic mutation in p110β.
• This mutation activates p110β by increasing its basal membrane association, contributing to oncogenesis.
• Targeting p110β may offer new therapeutic strategies for cancers harboring this mutation.