Characterization of Apin, a secreted protein highly expressed in tooth-associated epithelia

• Published in: Journal of cellular biochemistry 2008-02, Vol.103 (3), p.941-956
• Main Authors: Moffatt, Pierre, Smith, Charles E., St-Arnaud, René, Nanci, Antonio
• Format: Article
• Language: English
• Subjects: ameloblast; Ameloblasts - cytology; Ameloblasts - metabolism; Amino Acid Sequence; Amyloid - chemistry; Amyloid - genetics; Amyloid - metabolism; Animals; basement membrane; Cell Line; Cloning, Molecular; Conserved Sequence; Dental Enamel Proteins - genetics; Dental Enamel Proteins - metabolism; enamel organ; Enamel Organ - secretion; Epithelial Attachment - cytology; Epithelial Attachment - metabolism; Epithelium - secretion; Extracellular Matrix Proteins - chemistry; Extracellular Matrix Proteins - genetics; Extracellular Matrix Proteins - metabolism; Gene Expression Regulation, Developmental; gingiva; Gingiva - cytology; Gingiva - secretion; Glycosylation; HeLa Cells; Humans; Incisor - chemistry; Incisor - metabolism; junctional epithelium; Mice; Odontogenic Tumors - chemistry; Odontogenic Tumors - genetics; Odontogenic Tumors - metabolism; Phosphorylation; Protein Biosynthesis; Rats; secreted protein; Sequence Alignment; Swine; tooth; Transcription, Genetic
• ISSN: 0730-2312; 1097-4644
• DOI: 10.1002/jcb.21465

We previously reported expression of a protein by enamel organ (EO) cells in rat incisors, originally isolated from the amyloid of Pindborg odontogenic tumors called Apin. The aim of the present study was to further characterize the Apin gene and its protein in various species, assess tissue specificity, and clarify its localization within the EO. Northern blotting and RT‐PCR revealed that expression of Apin was highest in the EO and gingiva, moderate in nasal and salivary glands, and lowest in the epididymis. The protein sequences deduced from the cloned cDNA for rat, mouse, pig, and human were aligned together with those obtained from four other mammal genomes. Apin is highly conserved in mammals but is absent in fish, birds, and amphibians. Comparative SDS–PAGE analyses of the protein obtained from bacteria, transfected cells, and extracted from EOs all indicated that Apin is post‐translationally modified, a finding consistent with the presence of predicted sites for phosphorylation and O‐linked glycosylation. In rodent incisors, Apin was detected only in the ameloblast layer of the EO, starting at post‐secretory transition and extending throughout the maturation stage. Intense labeling was visible over the Golgi region as well as on the apices of ameloblasts abutting the enamel matrix. Apin was also immunodetected in epithelial cells of the gingiva which bind it to the tooth surface (junctional epithelium). The presence of Apin at cell‐tooth interfaces suggests involvement in adhesive mechanisms active at these sites, but its presence among other epithelial tissues indicates Apin likely possesses broader physiological roles. J. Cell. Biochem. 103: 941–956, 2008. © 2007 Wiley‐Liss, Inc.