Characterization of a human osteoblastic osteosarcoma cell line (SAOS-2) with high bone alkaline phosphatase activity

Abstract

We characterized the alkaline phosphatase activity of the human osteogenic sarcoma cell line, SAOS-2, and studied the regulation of this enzyme and 3',5'-cyclic adenosine monophosphate levels by 1,25-dihydroxyvitamin D₃ and triamcinolone acetonide. We report that the basal alkaline phosphatase activity of SAOS-2 cells was 100–1000 times greater than that of other established human osteogenic sarcoma cell lines. The enzymatic activity was thermolabile, could be inhibited by levamisole and L-homoarginine, but not by L-phenylalanine, and was immunoprecipitable with anti-bone/liver/kidney, but not with anti-placental antibody, confirming that it is the tissue-unspecific or bone/liver/kidney isoenzyme. However, in contrast to other established human osteosarcoma cell lines (TE-85, SAOS-1), in which alkaline phosphatase activity is stimulated several-fold by the steroid hormones 1,25-dihydroxyvitamin D₃ and hydrocortisone, the alkaline phosphatase activity of SAOS-2 cells was not affected by 1,25-dihydroxyvitamin D₃ treatment despite the presence of classical receptors for this hormone. Furthermore, administration of the potent glucocorticoid analogue, triamcinolone acetonide, induced only a modest increase in activity. The SAOS-2 cell line expressed low basal cAMP levels (28 pmol/10⁶ cells) which could be increased 25–40 times by pretreatment with parathyroid hormone. However, unlike other osteoblastic models, in which PTH-induced cAMP stimulation is modulated by 1,25-dihydroxy vitamin D₃ and glucocorticoids, neither of these hormones had an effect on the PTH-stimulated cAMP levels in SAOS-2 cells. We conclude that the SAOS-2 cell line is an osteoblastic cell model which expresses high levels of tissue-unspecific alkaline phosphatase activity and exhibits limited responsiveness to two steroid hormones. These cells may prove useful in determining the structure and processing of alkaline phosphatase and in studying other features of the osteoblastic phenotype, such as cAMP production, and their hormonal regulation.