A Rap/phosphatidylinositol 3-kinase pathway controls pseudopod formation [corrected]

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• GbpD, a Dictyostelium guanine nucleotide exchange factor for Rap1, is linked to cell adhesion, polarity, and chemotaxis.
• Rap1-regulated cell-substrate adhesion is mediated by the Phg2 kinase, but not cell polarity or chemotaxis.

Purpose of the Study:

• Investigate the molecular mechanisms underlying GbpD-mediated cell morphology and adhesion.
• Determine the role of PI3K in the GbpD signaling pathway.
• Explore the conservation of the Rap/PI3K pathway in cell polarity establishment.

Main Methods:

• Overexpression of GbpD in wild-type and pi3k1/2-null Dictyostelium cells.
• Analysis of cell adhesion, morphology, and pseudopod formation.
• Investigation of Rap1 binding to PI3K.
• Measurement of PIP3 levels and effects of PTEN overexpression.

Main Results:

• GbpD overexpression in pi3k1/2-null cells did not induce the adhesion and cell morphology phenotype.
• Rap1 directly binds to the Ras binding domain of PI3K.
• GbpD overexpression enhanced PIP3 levels, and PTEN overexpression reversed the GbpD-induced phenotype.
• A GbpD/Rap/PI3K pathway regulates pseudopod formation and cell polarity.

Conclusions:

• The GbpD/Rap/PI3K pathway is crucial for controlling pseudopod formation and cell polarity in Dictyostelium.
• This pathway represents a conserved mechanism for establishing cell polarity, as evidenced by its role in mammalian neuronal polarity.