Abstract
Calcium (Ca2+) signaling-dependent systems, such as the epidermal differentiation process, must effectively respond to variations in Ca2+ concentration. Members of the Ca2+-binding proteins play a central function in the transduction of Ca2+ signals, exerting their roles through a Ca2+-dependent interaction with their target proteins, spatially and temporally. By performing a suppression subtractive hybridization screen we identified a novel mouse gene, Scarf (skin calmodulin-related factor), which has homology to calmodulin (CaM)-like Ca2+-binding protein genes and is exclusively expressed in differentiating keratinocytes in the epidermis. The Scarf open reading frame encodes a 148-amino acid protein that contains four conserved EF-hand motifs (predicted to be Ca2+-binding domains) and has homology to mouse CaM, human CaM-like protein, hClp, and human CaM-like skin protein, hClsp. The functionality of Scarf EF-hand domains was assayed with a radioactive Ca2+-binding method. By Southern blot and computational genome sequence analysis, a highly related gene, Scarf2, was found 15 kb downstream of Scarf on mouse chromosome 13. The functional Scarf Ca2+-binding domains suggest a role in the regulation of epidermal differentiation through the control of Ca2+-mediated signaling.
Highlights
Calcium (Ca2؉) signaling-dependent systems, such as the epidermal differentiation process, must effectively respond to variations in Ca2؉ concentration
Protein sequence comparisons determined that Scarf presented 56.7% similarity to mouse CaM, 64.2% to hClp, and 64.9% hClsp (Fig. 1C)
By performing an Suppression Subtractive Hybridization (SSH) screen between the undifferentiated and differentiated cells of the neonatal mouse epidermis, we identified a novel murine Ca2ϩ-binding protein gene we termed Scarf
Summary
Vol 278, No 48, Issue of November 28, pp. 47827–47833, 2003 Printed in U.S.A. The Novel Murine Ca2؉-binding Protein, Scarf, Is Differentially Expressed during Epidermal Differentiation*. The differentiation process can be recapitulated partially in mouse keratinocytes cultivated in vitro by increasing the Ca2ϩ concentration in the culture medium [3] and is associated with the activation of protein kinase C (PKC) [4] This produces a situation that mimics the endogenous Ca2ϩ gradient present in the skin, with low extracellular levels surrounding the basal cells and increasing levels toward the upper granular layers [5]. A crucial role for the transduction of the Ca2ϩ signal is accomplished by members of the Ca2ϩ-binding proteins, which are characterized by the presence of a common helix-loop-helix structural motif in their Ca2ϩ-binding domain, termed EFhand [6] These proteins function by undergoing conformational changes upon binding of Ca2ϩ, allowing the association and regulation of activity of a range of specific target proteins. We propose that Scarf and Scarf are new members of the CaM-like proteins with potential roles in the Ca2ϩ-dependent epidermal differentiation process
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