Analysis of the genes encoding the spp24 protein in human and mouse and identification of interacting proteins
Secreted phosphoprotein 24 (spp24) is a member of the cystatin superfamily.;This study identifies a rare single-amino acid polymorphism (p.S38F) of human spp24 and its importance has been assessed by comparing the sequence of human spp24 with that of eight other species. The gene encoding spp24 in mouse (Spp2), like its human ortholog, comprises eight exons with an apparently TATA-les promoter. The exon-intron structure is identical in mouse and human and the size and location of intron 1 is conserved between many species. Using several strategies, the gene encoding spp24 in mouse has been mapped to 88832387-88853226 bp of the mouse chromosome 1. An extensive expression study was carried out on the mouse and human genes encoding spp24. These studies indicated that the gene has an expression pattern of a tissue-specific and cell-specific nature, being expressed predominantly in liver and its expression is down-regulated by lipopolysaccharide (LPS) and tumour necrosis factor alpha (TNFalpha). In an attempt to elucidate the function of the spp24 protein in mouse, a pooled-tissues cDNA library was constructed in a yeast two-hybrid vector. Two different constructs comprising the entire spp24 protein and the C-terminal non-cystatin like domain of the protein were used individually as baits in the yeast two-hybrid system to screen the constructed library. Seven potential interacting proteins were identified including granulin precursor also known as acrogranulin/epithelin (Grn), tissue specific transplantation antigen P35B (Tsta3), keratin complex 1, acidic, gene 18 (Krt1-18), keratin complex 1, acidic, gene 13 (Krtl-13 ), vimentin (Vim), similar to protein phosphatase 1, regulatory (inhibitor) subunit 12C (no gene symbol yet assigned) or myosin binding subunit 85 and alpha-actinin-4 (Actn4).