Expression of inhibitory G proteins in adenomatous thyroid glands obtained from hyperthyroid cats.
OBJECTIVE
To identify within guanosine triphosphate-binding proteins (G proteins) the subset of inhibitory G proteins (G) that have decreased expression in adenomatous thyroid glands obtained from hyperthyroid cats.


METHODS
Adenomatous thyroid glands obtained from 5 hyperthyroid cats and normal thyroid glands obtained from 3 age-matched euthyroid cats.


METHODS
Expression of G(i1), G(i2), and G(i3) in enriched membrane preparations from thyroid glands was quantified by use of immunoblotting with G(i) subtype-specific antibodies.


RESULTS
Expression of G(i2) was significantly decreased in tissues of hyperthyroid glands, compared with expression in normal thyroid tissue. Expression of G(i1) and G(i3) was not significantly different between normal thyroid tissues and tissues from hyperthyroid glands.


CONCLUSIONS
A decrease in G(i2) expression decreases inhibition of adenylyl cyclase and allows a relative increase in stimulatory G protein expression. This results in increased amounts of cAMP and subsequent unregulated mitogenesis and hormone production in hyperthyroid cells. Decreased G(i2) expression may explain excessive growth and function of the thyroid gland in cats with hyperthyroidism.
Ward
Cynthia R
CR
Department of Clinical Studies, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA 19104-6010, USA.
Achenbach
Sara E
SE
Peterson
Mark E
ME
Drobatz
Kenneth J
KJ
Holt
David
D
D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D015153:Blotting, Western / Q000662:veterinary; D002371:Cat Diseases / Q000378:metabolism*; D002415:Cats; D000242:Cyclic AMP / Q000378:metabolism; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000378:metabolism*; D005786:Gene Expression Regulation; D006980:Hyperthyroidism / Q000378:metabolism / Q000662:veterinary*; D013961:Thyroid Gland / Q000378:metabolism*
D000242:Cyclic AMP; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D000262:Adenylyl Cyclases