OPPOSITE REGULATION OF THROMBOSPONDIN-1 AND CORTICOTROPIN-INDUCED SECRETED PROTEIN THROMBOSPONDIN-2 EXPRESSION BY ADRENOCORTICOTROPIC HORMONE IN ADRENOCORTICAL-CELLS

Corticotropin-induced secreted protein (CISP) is a trimeric glycoprote in secreted by primary cultures of bovine adrenortical cells in respon se to adrenocorticotropic hormone (ACTH). This protein was recently pu rified in our laboratory, and its N-terminal amino-acid sequence revea led a significant similarity with thrombospondin-2 (TSP2). We report h ere the nucleotide sequence of a 386 bp RT-PCR fragment specific for C ISP. The deduced protein sequence shares 84% identity with the N-termi nal portion of mature human TSP2, suggesting that CISP is its bovine c ounterpart. Northern analysis of adrenocortical cell RNA using the abo ve cDNA fragment as a probe revealed a 6.0 kb CISP/TSP2 mRNA whose abu ndance was increased nearly fivefold following a 24 h cell treatment w ith 10(-7) M ACTH. Under the same conditions, the expression of TSP1 m RNA was reduced by tenfold. The protein levels of TSP1 and CISP/TSP2 v aried accordingly with their respective mRNA levels, as shown by immun oprecipitation and immunofluorescence experiments. Taken together, the se data show that ACTH induces a dramatic shift in the pattern of adre nocortical cell thrombospondin expression from TSP1 to CISP/TSP2. This observation suggests that these two members of the thrombospondin fam ily exert distinct biological functions in the adrenal cortex. This hy pothesis is further supported by the observation that anti-CISP antibo dies inhibit the maintenance of the morphological changes of bovine ad renocortical cells induced by ACTH, whereas anti-TSP1 antibodies do no t. (C) 1996 Wiley-Liss, Inc.