Implications of Desmoplakin Misregulation in Inherited Human Skin Diseases: Involvement of SERCA2 and PKC Alpha Signaling

Desmoplakin (DP) is a cytolinking protein that provides epithelial and cardiac tissues with structural integrity by anchoring the intermediate filament (IF) cytoskeleton to sites of cell-cell contact known as desmosomes. In order to maintain tissue homeostasis, desmosomes must form robust intercellular adhesion to withstand constant mechanical stress, but also be able to rapidly disassemble and reassemble during morphogenetic processes such as development and wound healing. I propose that there are regulatory factors that govern the DP-IF association, promote DP translocation during desmosome assembly, and establish intercellular adhesive strength. Furthermore, in addition to DP being directly targeted in genetic skin diseases, perturbations in these regulatory factors resulting in alterations of any of these subcellular processes may also be an underlying basis for pathogenesis.;Here, I have determined the effects of expressing a phospho-deficient DP S2849G C-terminal point mutant, which abrogates a PKC/A consensus site in the IF-binding domain. Cells expressing the DP S2849G point mutant exhibit aberrant DP-IF association, delayed DP translocation during desmosome assembly, and an altered adhesive. Fittingly, similar results were also observed following pharmacologic or genetic inhibition of PKCalpha signaling, suggesting that PKCalpha may play a role in the post-translational modification of DP S2849. I discovered that PKCalpha signaling is attenuated in cells deficient for the intracellular calcium pump SERCA2, which is defective in keratinocytes from patients with the acantholytic skin disorder Darier's disease (DD). SERCA2-deficient cells also exhibit impaired DP function similar to that observed following PKCalpha depletion and DP S2849G expression. Importantly, the atypical DP localization, desmosome assembly and intercellular adhesive strength caused by SERCA2-deficiency could be restored to levels comparable to control cells by stimulation of PKCalpha. The data suggest that PKCalpha agonists may serve as potential DD therapeutics by promoting the restoration of intercellular adhesive strength.;Altogether, these studies have revealed novel factors, such as PKCalpha and SERCA2, as being responsible for regulating DP localization, desmosome assembly and intercellular adhesive strength. Additionally, through the use of primary keratinocytes isolated from patients with genetic skin disorders, my findings have furthered the understanding of the pathogenic mechanisms underlying these inherited diseases and proposed possible new avenues for therapeutic research.