Figure 4.
Figure 4. Caspase-14 protects the skin against UVB photo damage and water loss and is involved in the processing of (pro)filaggrin. Caspase-14 expression starts in the spinous layer (indicated in shades of red), and cleavage into its p20 and p10 subunits occurs at the transition of the granular to the cornified layer. Caspase-14 is active in the dehydrating environment of the cornified layer, where it has an important function in formation of the epidermal barrier leading to protection against UVB and water loss (Denecker et al., 2007). Profilaggrin is a large structural molecule consisting of an N-terminal A domain and a B domain followed by multiple filaggrin repeats and a unique C-terminal sequence (for review see Candi et al., 2005). Profilaggrin undergoes many posttranslational modifications, eventually leading to release from the keratin intermediate filaments (see the section on the function of caspase-14 for details). In the lower stratum corneum, dehydration triggers the degradation of filaggrin monomers into free hygroscopic amino acids. These amino acids compose ∼40% of the natural moisturizing factors present in the stratum corneum and are important for maintaining epidermal hydration (Rawlings and Matts, 2005). In caspase-14–deficient skin, accumulating filaggrin fragments are present (Denecker et al., 2007), indicating that an unidentified protease (asterisk) cleaves the filaggrin monomer into these fragments and that caspase-14 is responsible for the further processing and degradation of these fragments into free amino acids. As it is very unlikely that caspase-14 is directly responsible for degradation of the filaggrin fragments into free amino acids, we propose two possible mechanisms: (1) caspase-14 could first cleave these filaggrin fragments, leading to further degradation into free amino acids by another endo- and/or exopeptidase; or (2) caspase-14 could directly or indirectly (by inactivating an inhibitor) activate an endo- and/or exopeptidase that further processes the smaller filaggrin fragments. KG, keratohyalin granule; KIF, keratin intermediate filament; NMF, natural moisturizing factors; SB, stratum basale; SC, stratum corneum; SG, stratum granulosum; SS, stratum spinosum; TG, transglutaminase.

Caspase-14 protects the skin against UVB photo damage and water loss and is involved in the processing of (pro)filaggrin. Caspase-14 expression starts in the spinous layer (indicated in shades of red), and cleavage into its p20 and p10 subunits occurs at the transition of the granular to the cornified layer. Caspase-14 is active in the dehydrating environment of the cornified layer, where it has an important function in formation of the epidermal barrier leading to protection against UVB and water loss (Denecker et al., 2007). Profilaggrin is a large structural molecule consisting of an N-terminal A domain and a B domain followed by multiple filaggrin repeats and a unique C-terminal sequence (for review see Candi et al., 2005). Profilaggrin undergoes many posttranslational modifications, eventually leading to release from the keratin intermediate filaments (see the section on the function of caspase-14 for details). In the lower stratum corneum, dehydration triggers the degradation of filaggrin monomers into free hygroscopic amino acids. These amino acids compose ∼40% of the natural moisturizing factors present in the stratum corneum and are important for maintaining epidermal hydration (Rawlings and Matts, 2005). In caspase-14–deficient skin, accumulating filaggrin fragments are present (Denecker et al., 2007), indicating that an unidentified protease (asterisk) cleaves the filaggrin monomer into these fragments and that caspase-14 is responsible for the further processing and degradation of these fragments into free amino acids. As it is very unlikely that caspase-14 is directly responsible for degradation of the filaggrin fragments into free amino acids, we propose two possible mechanisms: (1) caspase-14 could first cleave these filaggrin fragments, leading to further degradation into free amino acids by another endo- and/or exopeptidase; or (2) caspase-14 could directly or indirectly (by inactivating an inhibitor) activate an endo- and/or exopeptidase that further processes the smaller filaggrin fragments. KG, keratohyalin granule; KIF, keratin intermediate filament; NMF, natural moisturizing factors; SB, stratum basale; SC, stratum corneum; SG, stratum granulosum; SS, stratum spinosum; TG, transglutaminase.

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