A matched observational study of survival in cats with enucleation due to diffuse iris melanoma.

Although a small number of cases of feline diffuse iris melanoma have been documented to metastasize, the prognosis is not known. In this matched observational study, the survival time of 34 cats with enucleation due to histologically confirmed diffuse iris melanoma was recorded. These results are compared to the survival times of 83 age-matched control cats. Affected cats had enucleation between 2 and 10 years prior to the study. One group of control cats with eye disease had enucleation for either lymphoplasmacytic uveitis (27 cases), ocular trauma (seven cases), or endophthalmitis (four cases). In these control cats, enucleations were performed between 2 and 10 years prior to this study. Forty-five additional control cats presented for vaccination between 2 and 10 years prior to the study. The extent of diffuse iris melanoma at the time of enucleation in affected cats was graded according to the extent of involvement of ocular tissues and the invasiveness of the tumor. Affected cats have a significantly decreased survival compared with control cats and cats with extensive tumors at the time of enucleation have the lowest survival rates. Cats with tumors confined to the iris survive at the same rate as controls. These results suggests that early enucleation is important to avoid premature death, presumed to be due to cancer metastasis in cats with diffuse iris melanoma.

Agonist regulation of D(2) dopamine receptor/G protein interaction. Evidence for agonist selection of G protein subtype.

The D(2) dopamine receptor has been expressed in Sf21 insect cells together with the G proteins G(o) and G(i2), using the baculovirus system. Expression levels of receptor and G protein (alpha, beta, and gamma subunits) in the two preparations were similar as shown by binding of [(3)H]spiperone and quantitative Western blot, respectively. For several agonists, binding data were fitted best by a two-binding site model in either preparation, showing interaction of expressed receptor and G protein. For some agonists, binding to the higher affinity site was of higher affinity in D(2)/G(o) than in the D(2)/G(i2) preparation. Some agonists exhibited binding data that were best fitted by a two-binding site model in D(2)/G(o) and a one-binding site model in D(2)/G(i2). Therefore, receptor/G protein interaction seemed to be stronger in the D(2)/G(o) preparation. Agonist stimulation of [(35)S]GTP gamma S (guanosine 5'-3-O-(thio)triphosphate) binding in the two preparations also gave evidence for higher affinity D(2)/G(o) interaction. In the D(2)/G(o) preparation, agonist stimulation of [(35)S]GTP gamma S binding occurred at higher potency for several agonists, and a higher stimulation (relative to dopamine) was achieved in D(2)/G(o) compared with D(2)/G(i2). Some agonists were able to stimulate [(35)S]GTP gamma S binding in the D(2)/G(o) preparation but not in D(2)/G(i2). The extent of D(2) receptor selectivity for G(o) over G(i2) is therefore dependent on the agonist used, and thus agonists may stabilize different conformations of the receptor with different abilities to couple to and activate G proteins.

Molecular determinants of selectivity in 5-hydroxytryptamine1B receptor-G protein interactions.

The recognition between G protein and cognate receptor plays a key role in specific cellular responses to environmental stimuli. Here we explore specificity in receptor-G protein coupling by taking advantage of the ability of the 5-hydroxytryptamine1B (5-HT1B) receptor to discriminate between G protein heterotrimers containing Galphai1 or Galphat. Gi1 can interact with the 5-HT1B receptor and stabilize a high affinity agonist binding state of this receptor, but Gt cannot. A series of Galphat/Galphai1 chimeric proteins have been generated in Escherichia coli, and their functional integrity has been reported previously (Skiba, N. P., Bae, H., and Hamm, H. E. (1996) J. Biol. Chem. 271, 413-424). We have tested the functional coupling abilities of the Galphat/Galphai1 chimeras to 5-HT1B receptors using high affinity agonist binding and receptor-stimulated guanosine 5'-3-O-(thio)triphosphate (GTPgammaS) binding. In the presence of betagamma subunits, amino acid residues 299-318 of Galphai1 increase agonist binding to the 5-HT1B receptor and receptor stimulation of GTPgammaS binding. Moreover, Galphai1 containing only Galphat amino acid sequences from this region does not show any coupling ability to 5-HT1B receptors. Our studies suggest that the alpha4 helix and alpha4-beta6 loop region of Galphas are an important region for specific recognition between receptors and Gi family members.