Abstract
Protein-tyrosine phosphatase 1B (PTP1B) is an important regulator of protein-tyrosine kinase-dependent signaling pathways. Changes in expression and activity of PTP1B have been associated with various human diseases; however, the mechanisms by which PTP1B expression is regulated have yet to be characterized. Previously, we have shown that the expression of PTP1B is enhanced by p210 Bcr-Abl and that PTP1B is a specific antagonist of transformation induced by this oncoprotein protein-tyrosine kinase. Here we have characterized the PTP1B promoter and demonstrate that a motif with features of a stress-response element acts as a p210 Bcr-Abl-responsive sequence, termed PRS. We have shown that three C(2)H(2) zinc finger proteins, namely Sp1, Sp3, and Egr-1, bind to PRS. Whereas binding of either Sp1 or Sp3 induced promoter function, Egr-1 repressed Sp3-mediated PTP1B promoter activation. The binding of Egr-1 to PRS is suppressed by p210 Bcr-Abl due to the inhibition of Egr-1 expression, resulting in the enhancement of PTP1B promoter activity. Our data indicate that Egr-1 and Sp family proteins play a reciprocal role in the control of expression from the PTP1B promoter.
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