PKD2 and RSK1 Regulate Integrin β4 Phosphorylation at Threonine 1736

Area of Science:

• Cell Biology
• Dermatology
• Molecular Biology

Background:

• Integrin α6β4 is crucial for keratinocyte adhesion to the basement membrane via hemidesmosomes (HDs).
• Phosphorylation of the β4 subunit disrupts the α6β4-plectin interaction, weakening cell adhesion and HDs.
• Previous work identified T1736 phosphorylation and its disruption of β4-plectin binding, with PKD1 involvement.

Purpose of the Study:

• To investigate the signaling pathways and kinases responsible for β4-T1736 phosphorylation under different stimuli.
• To elucidate the role of calcium and specific kinases in regulating β4-T1736 phosphorylation and HD stability.

Main Methods:

• Depletion of intracellular calcium ([Ca2+]i) and use of phosphatase inhibitors.
• Pharmacological inhibition and genetic manipulation (siRNA, overexpression) of specific kinases (PKD2, ERK1/2, RSK1).
• Analysis of β4-T1736 phosphorylation levels and hemidesmosome integrity following various treatments.

Main Results:

• Depleting [Ca2+]i enhanced PMA- and EGF-induced β4-T1736 phosphorylation by inhibiting calcineurin and activating ERK1/2.
• PMA-stimulated β4-T1736 phosphorylation in keratinocytes is mainly mediated by PKD2 downstream of PKCδ.
• EGF-stimulated β4-T1736 phosphorylation and HD dissolution depend on MAPK signaling, involving RSK1 activation.

Conclusions:

• Different extracellular stimuli (PMA, EGF) activate distinct signaling cascades leading to β4-T1736 phosphorylation.
• PKD2 and RSK1 are identified as key kinases mediating β4-T1736 phosphorylation, with implications for keratinocyte adhesion and HD regulation.