TISSUE NONSPECIFIC ALKALINE-PHOSPHATASE MAY BE A FUNCTION-RELATED MARKER IN RENAL PROXIMAL TUBULAR EPITHELIA AND IN VASCULAR ENDOTHELIA AS IT IS IN OSTEOBLASTS

Tissue non-specific alkaline phosphatase (TN-AP) is a multifunctional phosphatase and has a variety of substrates in vitro. In adults, TN-AP is highly expressed in osteoblasts, renal proximal tubular epithelia and vascular endothelia. In osteoblasts, it is well known that TN-AP p lays an important role in bone mineralization. Considering its many ac tivities in vitro, we hypothesize that TN-AP also plays a role in regu lating cellular activities in renal proximal tubular epithelia and vas cular endothelia. By using a stable gene transfection technique, we tr ansfected two cell lines with a rat TN-AP gene, one renal proximal tub ule-like (LLC-PK1), another vascular endothelia-like (Py-4-1). The eff ect of TN-AP expression was cell specific, In Py-4-1 cells, the forced TN-AP expression stimulates cellular behaviours associated with termi nal differentiation. This suggests that in vivo AP expression in certa in vascular endothelia may mark a terminal-differentiated subpopulatio n with less angiogenic potential. While, in LLC-PK1 cells, the forced TN-AP expression inhibited cellular transport function as demonstrated by delayed dome formation. By inference, TN-AP expression in renal pr oximal tubule in vivo should have a regulatory role in cellular transp ort. Our data suggest that TN-APs have roles as function-related marke rs in renal proximal tubular epithelia and vascular endothelia.