Profilaggrin is a major epidermal calcium-binding protein.

Abstract

Profilaggrin is a major highly phosphorylated protein component of the keratohyalin granules of mammalian epidermis. It contains 10 to 12 tandemly repeated filaggrin units and is processed into the intermediate filament-associated protein filaggrin by specific dephosphorylation and proteolysis during terminal differentiation of the epidermal cells. Later, filaggrin itself is degraded to free amino acids that participate in maintenance of epidermal flexibility. The present paper describes the structural organization of the 5' region of the human profilaggrin gene as well as the amino terminus of the profilaggrin protein. profilaggrin mRNA, are transcribed from the profilaggrin gene system at earlier stages of epidermal differentiation. The amino terminus of profilaggrin exhibits a significant homology to the small calcium-binding S100-like proteins. It contains two a-helical regions, termed EF-hands, that bind calcium in vitro. This is the first example of functional calcium-binding domains fused to a structural protein. We suggest that in addition to its role in filament aggregation and the maintenance of epidermal flexibility, profilaggrin may play an important role in the differentiation of the epidermis by autoregulating its own processing in a calciumdependent manner or by participating in the transduction of calcium signal in epidermal cells.Terminal differentiation of human epidermis involves the expression of sets of novel structural proteins including the keratin intermediate filaments (composed of keratins 1 and 10) and two other proteins, loricrin and profilaggrin, which are codeposited as keratohyalin granules (7,60). Loricrin is now known to be a principal component of the insoluble cell envelope to which it is covalently cross-linked both by disulfide bonds and by N-(y-glutamyl)lysine cross-links formed by the action of epidermal transglutaminases (24, 25). Profilaggrin has a completely different fate. This protein initially accumulates as an insoluble phosphorylated polyprotein precursor consisting largely of filaggrin repeats (36,44,55). It has a half-life of about 6 h, and at very late stages of differentiation, it is dephosphorylated and proteolytically processed into individual filaggrin molecules (22, 45, 51) that presumably interact with and align the keratin filaments in a plane parallel to the surface of the epidermis (8, 57, 58). Filaggrin itself has a half-life of only about 24 h in stratum corneum cells (45) and is degraded mostly into free amino acids that are required for maintenance of epidermal osmolarity and hence flexibility and perhaps even for immunological protection of the organism (9,43,56). Thus, on the basis of our current understanding, the product of the profilaggrin gene is ultimately utilized in at least two important functions in normal epidermis. This series of events is clearly abnormal in a number of diseases of cornification in the epidermis, particularly the various classes of ichthyoses (65). For example, in epidermolytic hyperkeratosis and lamellar ich-* Correspo...

S100A11, S100A10, Annexin I, Desmosomal Proteins, Small Proline-rich Proteins, Plasminogen Activator Inhibitor-2, and Involucrin Are Components of the Cornified Envelope of Cultured Human Epidermal Keratinocytes

“…Many of the S100 genes, including S100A10 (69, 70) and S100A11 (54,71), have been co-localized on the same chromosome as other epidermal structural protein genes, suggesting a possible function in skin. Thus, the S100 proteins join another keratinocyte envelope precursor, profilaggrin, as an EF hand-containing protein (72). Trychohyalin, a hair follicle protein, which may also be an envelope precursor, also contains an EF hand that may be functionally important (73).…”

Opposing activities of c-Fos and Fra-2 on AP-1 regulated transcriptional activity in mouse keratinocytes induced to differentiate by calcium and phorbol esters

“…In addition, AP-1 sequences from the calcium-responsive element of the human keratin 1 gene (gaTGATTCAct) (Hu et al, 1993;Rothnagel et al, 1993), from position 777 of the 5' region of the human pro®laggrin promoter (gaTGAATCAct) (Markova et al, 1993), and from one of the AP-1 sites (gtTGACTAAcg) at position 7288 of the 5' noncoding region of the human involucrin gene (LopezBayghen et al, 1996) were also cloned as 56 multimers into the same pBLCAT2 reporter construct (Figure 3a). Supershift analysis indicated that the composition of the AP-1 complexes bound to these sequences in 0.12 mM calcium was the same (not shown).…”

The three-dimensional structure of human S100A12

“…The exceptions found to date are the monomeric calbindin D 9k , which was suggested to have a calcium-buffering role (Szebenyj & Moffat, 1986), and p26olf, which is a single-chain molecule consisting of two almost identical S100-like domains (Miwa et al, 1998;Tanaka et al, 1999). In addition, two high molecular weight proteins, the intermediate ®lament-associated protein precursors pro®laggrin (Markova et al, 1993) and trichohyalin (Lee et al, 1993), contain S100-like domains. There are also exceptions in terms of calcium binding: for example, S100A10 (Re  ty et al, 1999) and the N-terminal loop of S100A7 (Brodersen et al, 1998) do not bind calcium, while S100A3 was reported to have very low af®nity for calcium (Fohr et al, 1995).…”