Occludin S408 phosphorylation regulates tight junction protein interactions and barrier function.

Area of Science:

• Cell Biology
• Molecular Biology
• Physiology

Background:

• The C-terminal tail of occludin, a tight junction protein, is extensively phosphorylated, but the functional roles of specific phosphorylation sites remain largely unknown.
• Understanding these roles is crucial for deciphering tight junction regulation and its impact on barrier function.

Purpose of the Study:

• To investigate the functional significance of occludin S408 phosphorylation mediated by Casein Kinase 2 (CK2).
• To elucidate the molecular mechanisms by which occludin S408 phosphorylation influences tight junction protein dynamics and interactions.

Main Methods:

• Utilized biochemical and biophysical techniques to assess the impact of CK2 inhibition on occludin phosphorylation and tight junction integrity.
• Employed protein exchange assays and co-immunoprecipitation to analyze the dynamic behavior and binding interactions of tight junction proteins.
• Investigated the effects of CK2 inhibition on IL-13-induced barrier dysfunction.

Main Results:

• Inhibition of CK2-mediated occludin S408 phosphorylation significantly increased transepithelial resistance by reducing cation flux.
• S408 dephosphorylation altered the dynamic exchange of occludin, ZO-1, claudin-1, and claudin-2, leading to a convergence of their mobile fractions.
• Specific ZO-1 domains were essential for increased claudin-2 exchange, indicating the formation of a phosphorylation-sensitive complex.
• CK2 inhibition reversed IL-13-induced barrier loss, highlighting the role of occludin S408 in inflammatory responses.

Conclusions:

• Occludin S408 dephosphorylation is a key regulator of paracellular permeability through modulation of tight junction protein dynamics and interactions.
• This mechanism involves remodeling of protein complexes containing occludin, ZO-1, and specific claudins (claudin-1, claudin-2).
• Targeting occludin S408 phosphorylation may offer a therapeutic strategy for managing inflammation-associated barrier dysfunction.