Identification of skeletal muscle protein-tyrosine phosphatases by amplification of conserved cDNA sequences.

Specific protein-tyrosine phosphatase (PTPase) enzymes that regulate signal transduction by the insulin receptor in target tissues have not been identified. We evaluated the expression of PTPase homologs in skeletal muscle since this tissue is the major site of insulin-mediated glucose disposal in vivo. A rat skeletal muscle cDNA pool was prepared with a set of degenerate oligonucleotide primers and PTPase cDNA sequences were amplified using pairs of "guess-mers" that were deduced from highly conserved residues within the known catalytic domains of these enzymes. Sequences encoding three "receptor-like" transmembrane PTPases were identified and two of these (known as LAR and LRP) were confirmed to be expressed in muscle by subsequent cDNA library screening and Northern blot analysis. The expression of the LAR and LRP PTPases in skeletal muscle suggests that these enzymes might have a role in the regulation of insulin action in muscle and other insulin-sensitive tissues.