CAPRINE HOMOLOG OF RODENT 5'-AMP-ACTIVATED PROTEIN-KINASE SUBUNIT ANDYEAST SNF4 CAT3 IS DOWN-REGULATED BY THYROID-HORMONE/

We isolated a cDNA, B12, that was down-regulated by thyroid hormone (T H) in the goat cerebellum, using a polymerase chain reaction (PCR)-bas ed subtractive hybridization and differential screening procedure. Nor thern blot analysis of RNA from cerebellum of T-4-treated and untreate d hypothyroid goats confirmed that clone B12 was TH-regulated with an average reduction in expression of 21% after 4 days of T-4 supplementa tion. Other tissues from a T-4-treated and an untreated hypothyroid go at also revealed down-regulation of B12, with the highest reduction in expression found in the thyroid gland (38%). Steady-state levels of t he approximately 1.8 kb B12 mRNA were higher in brain than in peripher al tissues. in situ hybridization showed that B12 mRNA in the brain is mainly present in various layers of the cerebellum and the cerebral c ortex, the hippocampus, and the olfactory tubercle and is predominantl y expressed in neurons. Sequence analysis of the caprine B12 cDNA clon e, and the murine homologue, revealed 61% similarity to SNF4/CAT3, a r egulator involved in the transcriptional control of glucose-repressibl e genes in yeast, and 99% identity to a rat 5'-AMP-activated protein k inase subunit, which is involved in the regulation of fatty acid, glyc ogen and isoprenoid metabolism. In view of these homologies, B12 might encode a regulator involved in distinct metabolic pathways and theref ore, TH might also affect gene expression indirectly by down-regulatio n of regulators like B12.