Ser⁷¹ Phosphorylation Inhibits Actin-Binding of Profilin-1 and Its Apoptosis-Sensitizing Activity

Area of Science:

• Molecular Biology
• Cell Biology
• Cancer Research

Background:

• Profilin-1 (Pfn1) is a key actin-binding protein with tumor suppressor properties.
• Pfn1 inhibits cellular proliferation and promotes apoptosis, interacting with actin and poly-L-proline (PLP) motif-containing proteins.
• Nuclear localization and PLP-binding are crucial for Pfn1's tumor growth inhibition, partly via interaction with the ENL protein in the Super Elongation Complex (SEC).

Purpose of the Study:

• To investigate the role of Pfn1 phosphorylation at Ser71 in its anticancer activities.
• To elucidate the mechanisms by which Pfn1 regulates chemotherapy-induced apoptosis and tumor growth.
• To identify the kinase responsible for Pfn1 phosphorylation at Ser71.

Main Methods:

• In vitro and in vivo assays to assess Pfn1's actin-binding and localization.
• Genetic and pharmacological experiments to study Pfn1 phosphorylation and its effects.
• Analysis of Pfn1's interaction with the Super Elongation Complex (SEC) and its impact on gene transcription.

Main Results:

• Phosphorylation of Pfn1 at Ser71 inhibits its actin-binding and promotes nuclear export.
• Cytoplasmic localization and actin-binding of Pfn1 are essential for chemotherapy-induced apoptotic sensitization.
• Reversible Ser71 phosphorylation/dephosphorylation regulates dynamic actin association, crucial for Pfn1-mediated tumor growth inhibition.
• Protein kinase A (PKA) was identified as the kinase responsible for phosphorylating Pfn1 at Ser71.

Conclusions:

• Pfn1's anticancer activities are spatially defined and regulated by ligand-binding and phosphorylation.
• Ser71 phosphorylation dictates Pfn1's subcellular localization and actin-binding, thereby modulating its tumor suppressor functions.
• Understanding Pfn1 regulation by PKA offers novel therapeutic strategies for cancer treatment.