Impaired Trafficking of the Desmoplakins in Cultured Darier's Disease Keratinocytes

Abstract

Darier's disease is an autosomal dominantly inherited skin disorder characterized by loss of adhesion between epidermal cells, breakdown of desmosome-keratin filaments, and abnormal keratinization. ATP2A2 has been identified as the causative gene of Darier's disease. This gene encodes the sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA) isoform 2 pump, which transports Ca2+ from the cytosol into the endoplasmic reticulum lumen to maintain a low cytosolic Ca2+ concentration. Using indirect immunofluorescence and biochemical analysis, we investigated the distribution of key desmosomal proteins in normal human and Darier's disease keratinocytes under various calcium conditions. We show that inhibition of SERCA by thapsigargin in normal human keratinocytes impairs the trafficking of the desmoplakins, desmoglein, and desmocollin to the cell surface; these proteins show a diffuse cytoplasmic distribution and, together with plakoglobin, form detergent-insoluble aggregates. In Darier's disease keratinocytes, only the trafficking of desmoplakin is significantly inhibited; in these cells, desmoplakin forms insoluble aggregates when extracted with mild detergent. In contrast, the transmembrane proteins desmoglein and desmocollin are efficiently transported to the cell surface. These proteins, along with plakoglobin, remain equally distributed between detergent-soluble and -insoluble fractions. We also demonstrate an interaction between SERCA2 and desmoplakin during differentiation. Our results provide further insights into the critical role of calcium ATPases in maintaining epidermal integrity.

The calcium ATPase SERCA2 regulates desmoplakin dynamics and intercellular adhesive strength through modulation of PKCα signaling

“…In addition, the possibility that aberrant DP localization during desmosome assembly may be due to protein misfolding has been raised (28). While we have not extensively studied the possible role of ER stress, we did not observe any changes in DP expression, overall ER structure, or apoptosis/cell growth in SERCA2-deficient cells (Supplemental Fig.…”

Four novel ATP2A2 mutations in Slovenian patients with Darier disease

“…In DD, the mutations in SERCA2 pumps support the importance of intracellular calcium homeostasis necessary for desmosomal adhesions. 5 A 2003 study using cultured DD keratinocytes found that trafficking in desmoplakin was significantly inhibited. Desmoplakin is a desmosomal component that plays a crucial role in linking DD plaques with cell-to-cell adhesion.…”

Intercellular Junction Assembly, Dynamics, and Homeostasis

“…The fact that PKCa also promotes desmosome assembly supports the idea that this kinase is important for maintaining a dynamic state, which would allow rapid desmosome remodeling in response to environmental cues. Desmosomes are also defective in patients with Darier's disease who have impaired calcium homeostasis because of mutations in the sarco(endo)plasmic reticulum Ca 2þ -ATPase (SERCA) isoform 2 pump (Sakuntabhai et al 1999;Dhitavat et al 2003). Although these abnormalities were suggested to arise from improper folding of desmoplakin, it also seems possible that alterations in calcium-dependent kinase activity could contribute to the observed defects.…”