The expression of novH in adrenocortical cells is down-regulated by TGFβ1 through c-Jun in a Smad-independent manner

Abstract

The human NOV secreted glycoprotein (NOVH) is abundant in the fetal and adult adrenal cortex. The amount of NOVH increases in benign adrenocortical tumors and decreases in malignant adrenocortical tumors, suggesting that NOVH plays a role in tumorigenesis in the adrenal cortex. Transforming growth factor β1 (TGF β1), fibroblast growth factor 2 (FGF2), and insulin growth factors (IGFs) play crucial roles in the physiology of the adrenal cortex. We investigated the effects of these factors on the expression of novH in the NCI H295R adrenocortical cell line. The amounts of NOVH protein and novH transcripts were down-regulated by TGF β1 and up-regulated by FGF2, whereas IGFs had no effect. Furthermore, the TGF β1-dependent inhibition of novH promoter activity was completely abrogated following site-directed mutation of two activating protein (AP-1) sequences (positions -473 and -447), whereas the stimulatory effect of FGF2 was not affected. Co-transfection with dominant negative forms of c-Jun and MEKK1 also abrogated novH-targeted regulation by TGF β1, whereas the overproduction of Smad proteins or dominant negative forms of Smad had no effect. Taken together, these results suggest that c-Jun and MEKK1 signaling but not Smad signaling are involved in the TGF β1-dependent decrease in NOVH in NCI H295R cells. In conclusion, our data provide evidence that novH is a new target of TGF β1; unlike other members of the CCN (cyr61, ctgf, nov) family, however, its expression is repressed rather than induced.