Grtp1, a novel gene regulated by growth hormone

An in vitro model of GH-responsive cells was subjected to microarray analys is to identify a novel gene regulated by GH. This 258 amino acid protein, w e term GH Regulated TBC Protein-1 (GRTP1), contains the TBC signature motif of GTPase activator proteins of Rab-like small GTPases. Northern blot anal ysis revealed a 1.3 kb major mRNA species, most abundant in testes. TaqMan assay confirmed that in the mouse, Grtp1 is expressed at highest levels in testes, with lesser abundance in intestine, kidney, lung, and liver. In the testis, expression of Grtp1 significantly increases post-pubertally. Admin istration of GH to mice increased levels of GRTP1 mRNA in testes (140%), bu t decreased GRTP1 mRNA abundance in kidney (50%) and liver (25%). Grtp1 was localized to mouse proximal chromosome 8. Orthologs of this protein are pr esent in human, mouse, rat, and drosophila suggesting that GRTP1 has an imp ortant biological role(s).