The phosphorylation of proteins at tyrosine residues is critical in cellular signal transduction, neoplastic transformation and control of the mitotic cycle. These mechanisms are regulated by the activities of both protein-tyrosine kinases (PTKs) and protein-tyrosine phosphatases (PTPases). As in the PTKs, there are two classes of PTPases: membrane associated, receptor-like enzymes and soluble proteins. Here we report the isolation of a complementary DNA clone encoding a new form of soluble PTPase, PTP1C. The enzyme possesses a large noncatalytic region at the N terminus which unexpectedly contains two adjacent copies of the Src homology region 2 (the SH2 domain) found in various nonreceptor PTKs and other cytoplasmic signalling proteins. As with other SH2 sequences, the SH2 domains of PTP1C formed high-affinity complexes with the activated epidermal growth factor receptor and other phosphotyrosine-containing proteins. These results suggest that the SH2 regions in PTP1C may interact with other cellular components to modulate its own phosphatase activity against interacting substrates. PTPase activity may thus directly link growth factor receptors and other signalling proteins through protein-tyrosine phosphorylation.

Functional cDNA clones coding for three isoforms of the human prostaglandin E receptor EP, subtype have been isolated from kidney and uterus cDNA libraries. The three isoforms, designated hEP,_,, hEP,_,, and hEP,_,,,, have open reading frames corresponding to 390,388 and 365 amino acids, respectively. They differ only in the length and amino acid composition of their carboxy-terminal regions, beginning at position 360. The human EP, receptor has seven predicted transmembrane spanning domains and therefore belongs to the G-protein-coupled receptor family. The rank order of potency for prostaglandins and related analogs in competition for [3H]PGE, specific binding to membranes prepared from transfected COS cells was comparable for all three isoforms, and as predicted for the EP, receptor, with PGEz = PGE, >> PGF, = iloprost > PGD, >> U46619. In addition, the EP,-selective agonist MB28767 was a potent competing ligand with an IC, value of 0.3 nM, whereas the EP,-selective antagonist AH6909 gave IC,, values of 2-7 PM and the EP,-selective agonist butaprost was inactive. In summary, we have cloned three isoforms of the human EP, receptor having comparable ligand binding properties.

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