| Research Abstract |
Alkaline phosphatases (ALP) are highly ubiquitous enzymes present in the majority of animals from bacteria to higher vertebrate. Although their wide distribution in nature has suggested that these enzymes should perform important biological functions, their detailed roles or natural substrates remain unknown.
Tissue-nonspecific ALP (TNSALP) is found in the bone, liver, kidney and other tissues, and its gene consists of 12 exons with the coding sequence beginning in the second exon. TNSALP is expressed at high levels in cells within mineralizing tissues, such as osteoblasts and odontoblasts. Recently, a non-coding first exon of TNSALP gene was identified in the liver message (liver-type) which differed from that of the previously known osteoblast-derived cDNA sequence (bone-type). Although these two mRNAs produce an identical protein, they have different promoter regions, In order to examine the expression of their mRNA type, we designed specific oligonucleotide primers and determined mR
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NA by reverse transcription-polymerase chain reaction (RT-PCR). We found that the TNSALP in human dental tissues express the bone-type isozymes and are regulated by the same transcriptional mechanism as in the bone.
Although, the physiological role of ALP is still largely unknown, genetic disorders involving this enzyme such as hypophosphatasia (HOPS) have been identified and they may provide important clues. HOPS is a disorder with autosomal recessive inheritance characterized by defects in skeletal mineralization due to the deficiency of TNSALP. We analyzed the TNSALP gene from five unrelated Japanese patients and discovered five new missense mutations using PCR-single strand conformation polymorphism (PCR-SSCP). Especially, a deletion of T at position 1735 (1735T-del) located in exon 12 has been detected in three genetically unrelated Japanese patients, which seems to be one of the hot spots among the causative mutations in Japanese HOPS patients. Expression of the mutant TNSALP gene using COS-1 cells demonstrated that the protein translated from the mutant 1735T-del had undetectable ALP activity. Less
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