Background
Mammalian target of rapamycin (mTOR) inhibitors suppress adrenal cortical carcinoma cell proliferation and cortisol production; the relationship between mTOR and aldosterone production has not been examined.
Conclusion
mTOR signaling has a critical role in transducing the AngII signal initiating aldosterone and cortisol synthesis in HAC15 cells and that inhibition of mTOR could be a therapeutic option for conditions associated with excessive renin-angiotensin system-mediated steroid synthesis.
Methods
HAC15 cells were incubated with an mTOR activator and several inhibitors including AZD8055 (AZD) in the presence and absence of angiotensin II (AngII). The expression of rapamycin-sensitive adapter protein of mTOR (Raptor) and rapamycin-insensitive companion of mTOR (Rictor), adaptor proteins of mTOR complex 1 and 2, respectively, were studied in the HAC15 cells and deleted by CRISPR/gRNA.
Results
The mTOR inhibitors decreased aldosterone induced by AngII. Inhibition of mTOR by AZD significantly suppressed AngII-induced aldosterone and cortisol formation in a dose-dependent manner, whereas the mTOR activator MHY had no effect. AZD did not alter forskolin-induced aldosterone production showing that it is specific to the AngII signaling pathway. AngII-mediated ERK and mTOR activation were suppressed by AZD, along with a concomitant dose-dependent reduction of AngII-induced steroidogenic enzymes including steroidogenic acute regulatory protein, 3β-hydroxysteroid dehydrogenase-type 2, CYP17A1, and aldosterone synthase protein. Furthermore, mTOR components ribosomal protein S6 kinase (P70S6K) and protein kinase B phosphorylation levels were decreased by AZD. As mTOR exerts its main effects by forming complexes with adaptor proteins Raptor and Rictor, the roles of these individual complexes were studied. We found an increase in the phosphorylation of Raptor and Rictor by AngII and that their CRISPR/gRNA-mediated knockdown significantly attenuated AngII-induced aldosterone and cortisol production.