Tissue-non-specific alkaline phosphatase mRNA expression and alkaline phosphatase activity following application of retinoic acid in cultured human dental pulp cells

Retinoic acid is a potent inducer of tissue-non-specific alkaline phosphata se (TNSALP) expression in various osteoblastic and fibroblastic cells, and may be involved in morphogenesis, cellular growth and differentiation. This study investigates the effects of retinoic acid on alkaline phosphatase ac tivity and TNSALP gene expression in human dental pulp cells. Cultured cell s were treated with various concentrations of retinoic acid (0, 10(-7): 10( -6), 10(-5) M) in 0.5% bovine serum albumin without serum. Alkaline phospha tase activity was determined by the rate of p nitrophenyl phosphate hydroly sis and was also assayed in the presence of various inhibitors and under th ermal inactivation. A set of specific oligonucleotide primers was selected, based on the nucleotide sequences of two human TNSALP mRNA (bone and liver ) types, and reverse transcription-polymerase chain reaction (RT-PCR) perfo rmed. Inhibitory and thermal inactivation experiments revealed that the ele vated alkaline phosphatase activity had properties of the TNSALP type. RT-P CR showed that retinoic acid enhanced the expression of bone-type TNSALP mR NA in pulp cells. However, the liver-type TNSALP mRNA was not detected. The se findings suggest that the high alkaline phosphatase activity of retinoic acid-treated dental pulp cells is associated with increased transcription of the bone-type mRNA of the TNSALP gene and not with liver-type. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.