Steroid sulfatase activity in osteoblast cells

We have demonstrated steroid sulfatase activity in osteoblast cells and characteristics of the enzyme were also investigated. Cell free homogenate of rat osteoblast cell line, UMR106-01 and human osteoblast cell lines, MG-63, HOS were incubated with [3H] dehydroepiandrosterone-sulfate (DHEA-sulfate) or [3H] estrone-sulfate (E1-sulfate). The formation of DHEA or E1 from the corresponding substrate was identified by crystallization to constant specific activity. Michaelis constant (K(m)) for DHEA-sulfate was estimated as 2.1 x 10(-8)M in UMR106-01, 7.4 x 10(-7)M in MG-63, 5.8 x 10(-7)M in HOS and that for E1-sulfate was 4.1 x 10(-7)M, 3.0 x 10(-7)M, 9.8 x 10(-7)M, respectively. The expression of steroid sulfatase messenger ribonucleic acid in human osteoblast cells, HOS and MG-63 was first demonstrated by reverse transcription-polymerase chain reaction. The existence of steroid sulfatase in human and rat osteoblast cells suggests that osteoblast cells have the capacity to convert circulating sulfo-conjugated steroids to more active androgens and estrogens. This may indicate an important role of bone in facilitating hormonal action.