PRL and pituitary gland adenoma: However, although human ACTH, GH or PRL-expressing pituitary adenoma show very high expression of the HH signaling inducer SHH and the HH target gene GLI1 (Pyczek et al. 2016), a direct link between Hh signaling (e.g. mutations or pathway overactivation) and tumor formation in the AL has not been confirmed.