We studied the expression of Sonic hedgehog (SHH), Smoothened (SMO), Patched1 (PTCH1) and GLI family zinc finger 1 (GLI1) in human adrenal and in adrenocortical tumors using immunohistochemistry and semi-quantitative reverse transcriptase-polymerase chain reaction. Modulation of GLI1 and SMO messenger ribonucleic acid (mRNA) expression was investigated with forskolin. The role of Hh-signaling was studied in NCI-H295R cells and in an immortalized primary cell line using the Hh-agonist smoothened agonist (SAG) and the Hh-antagonist cyclopamine.
The Hh-pathway components SHH, GLI1, PTCH1 and SMO were detectable in all adrenal glands. While in cortisol-producing adenomas (CPA), Hh-signaling expression levels were comparable to that in normal adrenal cortex, a much higher mRNA expression of GLI1, SMO and SHH was observed in non-producing adenomas (NPA). Interestingly, stimulation of cultured adrenal cells with forskolin led to a decrease in expression of GLI1 and SMO mRNAs. Antagonism of Hh-signaling resulted in a lower proliferation rate of adrenocortical cells, while Hh-agonism had no significant effect on adrenal cell proliferation.
Our data show Hh-signaling activity in adult adrenal glands. Activation of the PKA pathway results in lower expression of Hh-signaling proteins. This might explain the lower expression of the Hh components GLI1 and SMO in CPA in comparison to the higher expression in NPA. Hh-signaling might be involved in the tumorigenesis of NPA.