CaMKII nucleates an osmotic protein supercomplex to induce cellular bleb expansion

Area of Science:

• Cell biology
• Biophysics
• Molecular and Cellular Physiology

Background:

• Blebs are plasma membrane protrusions crucial for cell migration and proliferation.
• Previous research suggested actin cortex contraction drives bleb expansion, but the role of compartmentalized ions and proteins was unclear.

Purpose of the Study:

• To investigate the functional significance of Ca²⁺ ions and proteins within expanding blebs.
• To elucidate the mechanism of cytoplasmic fluid influx during bleb expansion.

Main Methods:

• The study involved analyzing the composition and behavior of protein complexes within expanding blebs.
• Investigated the role of Ca²⁺, CaMKII, and Mena in bleb expansion dynamics.

Main Results:

• Elevated Ca²⁺ levels trigger the assembly of a protein superstructure around the CaMKII holoenzyme, including Mena.
• This Ca²⁺-induced complex possesses intrinsic osmotic activity, promoting water influx.
• The complex directly contributes to the physical expansion of cell blebs.

Conclusions:

• A novel mechanism for bleb expansion is identified, driven by a Ca²⁺-activated protein superstructure.
• This discovery provides new insights into the regulation of cytoplasmic physicochemical properties during cell dynamics.