No abstract

To further our understanding of the molecular mechanism of Bcr ± Abl mediated transformation, a yeast two hybrid screen was used to identify proteins binding to the Abl tyrosine kinase. Two partial cDNAs encoding novel SH2 domain-containing proteins were cloned and designated Shd and She. Both have homology to Shb, a previously reported SH2 domain-containing protein.Northern blot analysis showed that She is expressed in heart, lung, brain, and skeletal muscle, while expression of Shd is restricted to the brain. The deduced amino acid sequence of the full length mouse Shd cDNA contains an amino-terminal proline-rich region, and a carboxyterminal SH2 domain. A bacterially expressed Shd domain bound multiple tyrosine-phosphorylated proteins with relative molecular weights of 200, 170, 130, 100, 90, 78, 72 and 32 kDa from K562 cell lysates. Shd contains ®ve YXXP motifs, a substrate sequence preferred by Abl tyrosine kinases. Shd was tyrosine phosphorylated in COS-7 cells co-transfected with Shd and c-Abl or Bcr ± Abl. These results suggest that Shd may be a physiological substrate of c-Abl and may function as an adapter protein in the central nervous system.

Somatostatin exerts multiple effects throughout the body by binding to specific somatostatin receptors. Two classes of somatostatin receptors, SRIF1 and SRIF2, have been distinguished biochemically and pharmacologically. Two cDNAs have been recently isolated that encode somatostatin receptors 1 and 2 (SSTR1 and SSTR2, respectively). The pharmacological characteristics of receptors expressing these cDNAs resemble those of the SRIF2 and SRIF1 classes of somatostatin receptors, respectively. We stably expressed the rat homologs of both receptors in Chinese hamster ovary (CHO) cells (type K1). These transfected cell lines recognized the endogenous ligands SS14 and SS28 with high affinity, whereas the synthetic analog MK678 identified only SSTR2. In preparations of CHO-SSTR1 or CHO-SSTR2 cells, SS14 and SS28 inhibited forskolin-stimulated adenylyl cyclase activity by approximately 35%, with ED50 values in the nanomolar range. The adenylyl cyclase inhibition was dependent upon the guanine nucleotide GTP and could be ablated with pertussis toxin preincubation. The present data indicate that SSTR1 and SSTR2 are coupled to inhibition of adenylyl cyclase via pertussis toxin- sensitive G-proteins.