IDENTIFICATION OF BONE-TYPE ALKALINE-PHOSPHATASE MESSENGER-RNA FROM HUMAN PERIODONTAL-LIGAMENT CELLS

Tissue-nonspecific-type alkaline phosphatase is found in the bone, liv er, kidney, and other tissues, and its gene consists of 12 exons with the coding sequence beginning in the second exon. Recently, an alterna tive non-coding first exon was identified in the liver message which d iffered from that of the previously known osteoblast-derived cDNA sequ ence. Although these two mRNAs produce an identical protein, they have different promoter regions. The periodontal ligament tissue expresses a high level of alkaline phosphatase activity. To identify its mRNA t ype, we isolated a full-length cDNA for alkaline phosphatase from a cu ltured human periodontal ligament cell expression library, using bone- derived tissue-nonspecific alkaline phosphatase cDNA as a hybridizatio n probe. The size of this clone was 2.5 kb, and its 5' and 3' untransl ated sequences were identical to those of the human tissue-nonspecific type isolated from osteoblastic cells but not to those of the Liver t ype. In addition, the same fragments as in bone-derived tissue-nonspec ific-type cDNA were detected by the treatment of the cDNA clone with r estriction enzymes Hinc II and Pst I. The results suggest that express ion of the same alkaline phosphatase isozyme in human periodontal liga ment cells may be regulated by the same transcriptional mechanism as i n bone.