Epidermal differentiation complex

The epidermal differentiation complex (EDC) is a gene complex comprising over fifty genes encoding proteins involved in the terminal differentiation and cornification of keratinocytes, the primary cell type of the epidermis. In humans, the complex is located on a 1.9 Mbp stretch within chromosome 1q21.[1][2] The proteins encoded by EDC genes are closely related in terms of function, and evolutionarily they belong to three distinct gene families: the cornified envelope precursor family, the S100 protein family and the S100 fused type protein (SFTP) family.[3]

It has been hypothesized that the clustering of EDC genes occurred due to duplication events which were evolutionarily favored during the adaptation to terrestrial environments.[3][4] EDC proteins have been involved in a variety of skin disorders including ichthyosis vulgaris, atopic dermatitis and psoriasis.[5]

History

The epidermal differentiation complex was first described in 1993,[1] and further characterized in 1996, when Dietmar Mischke and colleagues noted the "close functional cooperation among [eleven] structurally and evolutionary related genes".[2] By 2001, 37 genes had been identified as members of the EDC.[6] The number rose to 43 in 2002,[7] and by 2012 a total of 57 genes were considered part of the complex.[3]

EDC genes

Cornified envelope precursor family

As its name implies, the cornified envelope (CE) precursor family includes genes that encode the proteins forming the CE. The CE is a cross-linked matrix that surrounds terminally differentiated squamous keratinocytes after a process known as cornification. CE precursor proteins are cross-linked by transglutaminases.[3] The ratio of CE precursor proteins varies from tissue to tissue.[3] In the epidermis, the most abundant CE component is loricrin (65-70%), while involucrin is a minor component (<5%). The other CE proteins are classified as small proline-rich (SPRR) proteins, a subset of which is the late cornified envelope (LCE) protein group.[3]

Small proline-rich proteins (SPRR proteins)
Late cornified envelope proteins (LCE proteins)
  • LCE1A
  • LCE1B
  • LCE1C
  • LCE1D
  • LCE1E
  • LCE1F
  • LCE2A
  • LCE2B
  • LCE2C
  • LCE2D
  • LCE3A
  • LCE3B
  • LCE3C
  • LCE3D
  • LCE3E
  • LCE4A
  • LCE5A
  • LCE6A
  • LEP7

S100 family

The S100 family comprises 17 genes and 6 pseudogenes. S100 proteins contain two EF-hand motifs separated by a hinge region.[3] S100 proteins have various functions and are generally associated with abnormal epidermal differentiation.[3] S100A8 and S100A9 (calgranulin A and B, respectively), dimerize to form calprotectin. Calprotectin, psoriasin (S100A7) and knoeberisin (S100A15) are antimicrobial peptides.[3]

SFTP family

The S100 fused type protein (SFTP) family or fused gene family encompasses genes which are mainly expressed in stratified epithelia and play a role in epithelial homeostasis.[3][8] Like S100 proteins, SFTPs contain two calcium-binding EF-hand motifs.[3] These proteins are associated with cytoplasmic intermediate filaments as well as minor components of the CE.[3] Due to their homologous structure they are also known as filaggrin-like proteins.[9][10]

Regulation of EDC gene expression

EDC genes are transcriptionally controlled by various transcription factors such as krüppel-like factor 4 (KLF4), GATA3, grainyhead-like 3 (GRHL3), aryl hydrocarbon receptor nuclear translocator (ARNT) and NRF2.[3]

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References
  1. Volz, Armin; Korge, Bernhard P.; Compton, John G.; Ziegler, Andreas; Steinert, Peter M.; Mischke, Dietmar (October 1993). "Physical Mapping of a Functional Cluster of Epidermal Differentiation Genes on Chromosome 1q21". Genomics. 18 (1): 92–99. doi:10.1006/geno.1993.1430. PMID 8276421.
  2. Mischke, Dietmar; Korge, Bernhard P.; Marenholz, Ingo; Volz, Armin; Ziegler, Andreas (May 1996). "Genes Encoding Structural Proteins of Epidermal Cornification and S100 Calcium-Binding Proteins Form a Gene Complex ("Epidermal Differentiation Complex") on Human Chromosome 1q21". Journal of Investigative Dermatology. 106 (5): 989–992. doi:10.1111/1523-1747.ep12338501. PMID 8618063.
  3. Kypriotou, Magdalini; Huber, Marcel; Hohl, Daniel (September 2012). "The human epidermal differentiation complex: cornified envelope precursors, S100 proteins and the 'fused genes' family". Experimental Dermatology. 21 (9): 643–649. doi:10.1111/j.1600-0625.2012.01472.x. PMID 22507538.
  4. Backendorf, C; Hohl, D (October 1992). "A common origin for cornified envelope proteins?". Nature Genetics. 2 (2): 91. doi:10.1038/ng1092-91. PMID 1303269.
  5. Hoffjan, S; Stemmler, S (September 2007). "On the role of the epidermal differentiation complex in ichthyosis vulgaris, atopic dermatitis and psoriasis". British Journal of Dermatology. 157 (3): 441–449. doi:10.1111/j.1365-2133.2007.07999.x. PMID 17573887.
  6. Marenholz, I; Zirra, M; Fischer, DF; Backendorf, C; Ziegler, A; Mischke, D (March 2001). "Identification of human epidermal differentiation complex (EDC)-encoded genes by subtractive hybridization of entire YACs to a gridded keratinocyte cDNA library". Genome Research. 11 (3): 341–55. doi:10.1101/gr.114801. PMC 311024. PMID 11230159.
  7. Elder, James T.; Zhao, Xinping (October 2002). "Evidence for local control of gene expression in the epidermal differentiation complex" (PDF). Experimental Dermatology. 11 (5): 406–412. doi:10.1034/j.1600-0625.2002.110503.x. hdl:2027.42/71593.
  8. Wu, Zhihong; Hansmann, Britta; Meyer-Hoffert, Ulf; Gläser, Regine; Schröder, Jens-Michael; Egles, Christophe (22 April 2009). "Molecular Identification and Expression Analysis of Filaggrin-2, a Member of the S100 Fused-Type Protein Family". PLoS ONE. 4 (4): e5227. doi:10.1371/journal.pone.0005227. PMC 2668185. PMID 19384417.
  9. de Guzman Strong, C.; Conlan, S.; Deming, C. B.; Cheng, J.; Sears, K. E.; Segre, J. A. (20 January 2010). "A milieu of regulatory elements in the epidermal differentiation complex syntenic block: implications for atopic dermatitis and psoriasis". Human Molecular Genetics. 19 (8): 1453–1460. doi:10.1093/hmg/ddq019. PMC 2846160. PMID 20089530.
  10. Pellerin, Laurence; Henry, Julie; Hsu, Chiung-Yueh; Balica, Stéfana; Jean-Decoster, Catherine; Méchin, Marie-Claire; Hansmann, Britta; Rodriguez, Elke; Weindinger, Stefan; Schmitt, Anne-Marie; Serre, Guy; Paul, Carle; Simon, Michel (April 2013). "Defects of filaggrin-like proteins in both lesional and nonlesional atopic skin". Journal of Allergy and Clinical Immunology. 131 (4): 1094–1102. doi:10.1016/j.jaci.2012.12.1566. PMID 23403047.
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