PI3Kβ is selectively required for growth factor-stimulated macropinocytosis

Area of Science:

• Cell Biology
• Molecular Biology
• Cancer Biology

Background:

• Macropinocytosis is a non-selective cellular uptake process vital for immune surveillance, pathogen entry, and nutrient acquisition in tumors.
• Class I phosphoinositide 3-kinases (PI3Ks) are key regulators of cellular signaling pathways, including endocytosis.

Purpose of the Study:

• To investigate the specific role of class I PI3K isoforms in ligand-stimulated macropinocytosis.
• To elucidate the involvement of PI3Kβ in both normal and tumor cell macropinocytosis.

Main Methods:

• Utilized genetic manipulation to assess the impact of PI3Kβ loss on macropinocytosis.
• Investigated PI3Kβ's role in relation to receptor tyrosine kinase activation and Rac1 signaling.
• Examined PI3Kβ function in tumor cells with PTEN deficiency.

Main Results:

• Macropinocytosis is highly dependent on the PI3Kβ isoform (encoded by PIK3CB) upon receptor tyrosine kinase activation.
• Loss of PI3Kβ function impairs macropinocytosis at early stages and also affects later steps downstream of Rac1.
• PI3Kβ is indispensable for the heightened constitutive macropinocytosis observed in PTEN-deficient tumor cells.

Conclusions:

• PI3Kβ plays a critical and multifaceted role in regulating macropinocytosis.
• Targeting PI3Kβ with pharmacological inhibitors may offer novel therapeutic strategies for cancer treatment.