Fig. 7. Dephosphorylation of osteopontin by lysosomal acid phosphatases. (A) Western blot of recombinant mouse osteopontin incubated for 2 and 3 hours in the presence of bone extracts from control and LAP/Acp5-deficient animals, and analysed using antibodies to osteopontin. Note that the osteopontin immunoreactive bands have disappeared during incubation with control bone extracts while in LAP/Acp5-deficient bone extracts, the immunoreactivity is preserved. (B) Using anti-phosphoserine antibodies, the lack of dephosphorylation of osteopontin after incubation with LAP/Acp5 bone extracts is evident. The serine-phosphorylated osteopontin has disappeared after incubation with bone extracts from control mice. (C) In the presence of proteinase inhibitors, the immunoreactivity is still lost with control bone extracts, whereas inhibition of phosphatase activities with L-tartrate and molybdate prevented dephosphorylation of osteopontin.
