Filaggrin and filaggrin 2 processing are linked together through skin aspartic acid protease activation.

Skin aspartic acid protease (SASPase) is believed to be a key enzyme involved in filaggrin processing during epidermal terminal differentiation. Since little is known about the regulation of SASPase function, the aim of this study was to identify involved protein partners in the process. Yeast two hybrid analyses using SASPase as bait against a human reconstructed skin library identified that the N-terminal domain of filaggrin 2 binds to the N-terminal fragment of SASPase. This interaction was confirmed in reciprocal yeast two hybrid screens and by Surface Plasmon Resonance analyses. Immunohistochemical studies in human skin, using specific antibodies to SASPase and the N-terminal domain of filaggrin 2, showed that the two proteins partially co-localized to the stratum granulosum. In vitro enzymatic assays showed that the N-terminal domain of filaggrin 2 enhanced the autoactivation of SASPase to its 14 kDa active form. Taken together, the data suggest that the N-terminal domain of filaggrin 2 regulates the activation of SASPase that may be a key event upstream of filaggrin processing to natural moisturizing factors in the human epidermis.

Calmodulin-like skin protein level increases in the differentiated epidermal layers in atopic dermatitis.

In atopic dermatitis (AD), the skin barrier is disturbed, and the expression of calcium-dependent S100 proteins and the calcium gradient is also altered in the epidermis. The calmodulin-like skin protein (CLSP), which is expressed in the differentiated epidermis, is believed to modulate the function of calcium-dependent proteins involved in barrier formation and is significantly increased in the epidermis of psoriatic patients. We, therefore, investigated the CLSP level in skin biopsies taken from patients with acute exacerbated and non-exacerbated AD as well as from healthy control subjects. Immunohistochemical, Western blot and ELISA analyses showed significant increases (P < 0.03) in CLSP level in the epidermis from patients with acute exacerbated AD as compared to that from patients with non-exacerbated AD and from control subjects. Such increased expression of CLSP may help re-establish a functional epidermal barrier in acute AD.