Expression, regulation, and function of the SPR family of proteins. A review.
The small, proline-rich (SPR) genes consist of three subclasses closely linked on human chromosome 1, a region referred to as the epidermal differentiation complex. SPR genes consist of two exons, with the second exon containing the entire open reading frame. SPRs are expressed in all squamous tissues of the skin, scalp, footpad, vaginal epithelia, and most of the epithelial lining of the digestive tract, including the lip, tongue, esophagus, and forestomach. Although SPR1 is absent in normal mucociliary epithelium of the respiratory tract, epithelia that undergo squamous differentiation in response to vitamin-A deficiency or to injury owing to exposure to environmental toxicants express SPR1. High levels of SPR1 are detected in various diseases and cancers of the skin or respiratory epithelia and in nonkeratinizing papillary adenocarcinomas. SPR expression can be regulated by transcriptional factors, by posttranscriptional factors, or by factors that affect SPR1 mRNA translation or protein turnover. Furthermore, regulation can be affected by the state of cell proliferation. The presence of SPR1 in most of these epithelia, and the absence of SPR3 in normal skin, suggest that these subclasses have distinct functions. Various approaches to the study of the cross-linked envelope (CE) components in identifying SPR1 and SPR2 and in suggesting that SPRs are one of the precursor proteins of the CE. However, expression of SPR1 in nonsquamous tissues and cell lines indicates a function not associated with squamous differentiation. Several studies have demonstrated that SPR1 antibodies react with nuclear proteins and that SPR1 is expressed in cells before entering the G0 phase of the cell cycle. Future studies should clarify the role of SPRs by modifying their contents in CE, and should identify SPR-associated proteins to clarify the cell growth-related role of SPR1.
Tesfaigzi
J
J
Lovelace Respiratory Research Institute, Albuquerque, NM 87185, USA.
Carlson
D M
DM
D000375:Aging; D000595:Amino Acid Sequence; D000818:Animals; D016466:CHO Cells; D002118:Calcium / Q000378:metabolism; D002452:Cell Count; D002455:Cell Division; D016384:Consensus Sequence; D055233:Cornified Envelope Proline-Rich Proteins; D006224:Cricetinae; D016207:Cytokines / Q000378:metabolism; D004064:Digestive System / Q000378:metabolism; D004817:Epidermis / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D007381:Intermediate Filament Proteins / Q000378:metabolism*; D008175:Lung Neoplasms / Q000473:pathology; D008565:Membrane Proteins; D008969:Molecular Sequence Data; D005810:Multigene Family; D018307:Neoplasms, Squamous Cell / Q000473:pathology; D011506:Proteins / Q000378:metabolism*; D012137:Respiratory System / Q000378:metabolism; D012176:Retinoids / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D012867:Skin / Q000378:metabolism; D012878:Skin Neoplasms / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000378:metabolism; D013997:Time Factors; D014407:Tumor Cells, Cultured
D055233:Cornified Envelope Proline-Rich Proteins; D016207:Cytokines; D007381:Intermediate Filament Proteins; D008565:Membrane Proteins; D011506:Proteins; D012176:Retinoids; C491986:SPRR2B protein, human; C491987:SPRR2D protein, human; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium