Structural organization and regulation of the small proline-rich family of cornified envelope precursors suggest a role in adaptive barrier function.
The protective barrier provided by stratified squamous epithelia relies on the cornified cell envelope (CE), a structure synthesized at late stages of keratinocyte differentiation. It is composed of structural proteins, including involucrin, loricrin, and the small proline-rich (SPRR) proteins, all encoded by genes localized at human chromosome 1q21. The genetic characterization of the SPRR locus reveals that the various members of this multigene family can be classified into two distinct groups with separate evolutionary histories. Whereas group 1 genes have diverged in protein structure and are composed of three different classes (SPRR1 (2x), SPRR3, and SPRR4), an active process of gene conversion has counteracted diversification of the protein sequences of group 2 genes (SPRR2 class, seven genes). Contrasting with this homogenization process, all individual members of the SPRR gene family show specific in vivo and in vitro expression patterns and react selectively to UV irradiation. Apparently, creation of regulatory rather than structural diversity has been the driving force behind the evolution of the SPRR gene family. Differential regulation of highly homologous genes underlines the importance of SPRR protein dosage in providing optimal barrier function to different epithelia, while allowing adaptation to diverse external insults.
Cabral
A
A
Department of Molecular Genetics, Leiden Institute of Chemistry, P. O. Box 9502, 2300 RA Leiden, The Netherlands.
Voskamp
P
P
Cleton-Jansen
A M
AM
South
A
A
Nizetic
D
D
Backendorf
C
C
D000595:Amino Acid Sequence; D001483:Base Sequence; D002478:Cells, Cultured; D002878:Chromosomes, Human, Pair 1; D020451:Contig Mapping; D055233:Cornified Envelope Proline-Rich Proteins; D003360:Cosmids / Q000378:metabolism; D019143:Evolution, Molecular; D005091:Exons; D015723:Gene Library; D006801:Humans; D007381:Intermediate Filament Proteins / Q000235:genetics; D015603:Keratinocytes / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics*; D008957:Models, Genetic; D008969:Molecular Sequence Data; D010455:Peptides / Q000235:genetics; D020161:Physical Chromosome Mapping; D011392:Proline / Q000737:chemistry*; D055232:Proline-Rich Protein Domains; D011401:Promoter Regions, Genetic; D011498:Protein Precursors / Q000235:genetics*; D011506:Proteins / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid; D012689:Sequence Homology, Nucleic Acid; D014018:Tissue Distribution; D014466:Ultraviolet Rays
D055233:Cornified Envelope Proline-Rich Proteins; D007381:Intermediate Filament Proteins; D008565:Membrane Proteins; D010455:Peptides; D011498:Protein Precursors; D011506:Proteins; C491986:SPRR2B protein, human; C491987:SPRR2D protein, human; C064554:loricrin; C032253:involucrin; D011392:Proline