Transient expression of the tartrate-resistant acid phosphatase (TRAP) gene in hamster cells: a pilot study

Tartrate-resistant acid phosphatase (TRAP) became known as the characteristic, albeit not specific, marker enzyme for hairy cell leukemia (HCL). It is also expressed in other types of leukemic cells and in a variety of normal hematopoietic cells under both physiological and artificial conditions. The role of this distinctive enzyme is still unknown. TRAP hydrolyzes several chemical compounds, but its physiological substrate remains to be elucidated. Here, the insertion of a human TRAP cDNA into mammalian expression vector pSBC-2 yielded a construct that encoded enzymatically active TRAP in transfected baby hamster kidney cells (BHK-21). TRAP was expressed transiently, as shown by Northern blot analysis, polyacrylamide gel electrophoresis, isoelectric focusing and cytochemical staining. BHK-21 cells over-expressing the enzyme had a growth rate that was approximately 50% of that observed in control cells. A stable expression could not be achieved. Recent evidence suggested that TRAP might function as a protein tyrosine phosphatase. The effect of TRAP on protein tyrosine phosphorylation was examined by immunoblotting with an anti-phosphotyrosine monoclonal antibody (MoAb). The level of tyrosine phosphorylation was clearly lower in transfected BHK-21-TRAP cells than in the control cultures. Phorbol ester-mediated induction of protein tyrosine phosphorylation could overcome the status of reduced phosphorylation in BHK-21-TRAP cells. Furthermore, upon treatment with 12-O-tetra-decanoylphorphol-13-acetate tyrosine phosphorylation reached similar levels to stimulated control cells, indicating the existence of a functional endogenous phosphorylation network. Thus, TRAP might function as an antagonistic counterpart of cellular protein tyrosine kinases and could be involved in the control of cellular activation, proliferation, and differentiation.