EXPRESSION OF PROTEIN-TYROSINE PHOSPHATASES IN THE MAJOR INSULIN TARGET TISSUES

Protein-tyrosine phosphatases (PTPs) are key regulators of the insulin receptor signal transduction pathway. We have performed a detailed an alysis of PTP expression in the major human insulin target tissues or cells (liver, adipose tissue, skeletal muscle and endothelial cells). To obtain a representative picture, all tissues were analyzed by PCR u sing three different primer sets corresponding to conserved regions of known PTPs. A total of 24 different PTPs were identified. A multiprob e RNase protection assay was developed to obtain a semiquantitative me asure of the expression levels of selected PTPs. Surprisingly, PTP-LAR , previously suggested to be a major regulator of the insulin receptor tyrosine kinase, was expressed in extremely low levels in skeletal mu scle, whereas the related receptor-type PTP-sigma and PTP-alpha were e xpressed in relatively high levels in all four tissues. The low levels of LAR PTP mRNA in skeletal muscle were further confirmed by Northern blot analysis. (C) 1997 Federation of European Biochemical Societies.