Opposite regulation of thrombospondin-1 and corticotropin-induced secreted protein/thrombospondin-2 expression by adrenocorticotropic hormone in adrenocortical cells

Abstract

Corticotropin-induced secreted protein (CISP) is a trimeric glycoprotein secreted by primary cultures of bovine adrenortical cells in response to adrenocorticotropic hormone (ACTH). This protein was recently purified in our laboratory, and its N-terminal amino-acid sequence revealed a significant similarity with thrombospondin-2 (TSP2). We report here the nucleotide sequence of a 386 bp RT-PCR fragment specific for CISP. The deduced protein sequence shares 84% identity with the N-terminal portion of mature human TSP2, suggesting that CISP is its bovine counterpart. Northern analysis of adrenocortical cell RNA using the above cDNA fragment as a probe revealed a 6.0 kb CISP/TSP2 mRNA whose abundance was increased nearly fivefold following a 24 h cell treatment with 10(-7) M ACTH. Under the same conditions, the expression of TSP1 mRNA was reduced by tenfold. The protein levels of TSP1 and CISP/TSP2 varied accordingly with their respective mRNA levels, as shown by immunoprecipitation and immunofluorescence experiments. Taken together, these data show that ACTH induces a dramatic shift in the pattern of adrenocortical cell thrombospondin expression from TSP1 to CISP/TSP2. This observation suggests that these two members of the thrombospondin family exert distinct biological functions in the adrenal cortex. This hypothesis is further supported by the observation that anti-CISP antibodies inhibit the maintenance of the morphological changes of bovine adrenocortical cells induced by ACTH, whereas anti-TSP1 antibodies do not.

The Distribution of the Matricellular Protein Thrombospondin 2 in Tissues of Embryonic and Adult Mice

“…In keeping with our detection of TSP2 in the adrenal cortex, bovine adrenocortical cells were shown to express TSP2 in culture (Pellerin et al 1993). Furthermore, adrenocortical cells could be induced to overexpress TSP2 by treatment with ACTH (Lafeuillade et al 1996) or TGF-␤1 (Negoescu et al 1995).…”

Cloning and Expression of Murine SC1, a Gene Product Homologous to SPARC

“…In addition, the coincident expression of SC1 and SPARC mRNA in some organs (e.g., adrenal cortex and brain) supports the possibility that these proteins could compensate for each other functionally. It has been recently suggested, however, that thrombospondins 1 and 2 have distinct functions in the adrenal cortex, despite their homology and coincidence in this tissue (Lafeuillade et al 1996). Studies on mice with targeted disruption of either the SC1 or SPARC gene should address the question of compensation and will provide a more complete understanding of their functions in vivo.…”

Fine tuning of adrenocortical functions by locally produced growth factors

“…Of the different TGF isoforms, both TGF 1 and TGF 2 proteins are detectable in the fetal mouse adrenal whereas TGF 3 is not (Pelton et al 1991). In contrast, adult bovine adrenocortical cells express mainly TGF 1, TGF 3 slightly and TGF 2 not at all, as determined by reverse transcription PCR (Chambaz et al 1996). Given the redundancy of the effects triggered by these factors, these distinct patterns of expression may not reflect any difference in terms of biological effects.…”

“…Each complex appears to contain both covalent and non-covalent associations of the aforementioned proteins. Two physiological mechanisms of latent TGF activation have been reported in the literature: the proteolytic attack of LAP by plasmin and the interaction of latent TGF with thrombospondins (Flaumenhaft et al 1993, Feige et al 1996. Both latent TGF complexes present in the conditioned medium of bovine adrenocortical cells were incubated with either thrombospondin-1 or thrombospondin-2, and the release of active TGF was measured.…”

“…differentially regulated by ACTH in bovine adrenocortical cells (Lafeuillade et al 1996). Whereas thrombospondin-1 expression is inhibited by ACTH, thrombospondin-2 is one of the major secreted proteins induced by ACTH (Pellerin et al 1993).…”