CDKN2A and pituitary gland adenoma: Among our differentially expressed genes, some corroborated published studies that compared gene expression of normal pituitary tissue and pituitary adenomas: the overexpression of CCND1 and underexpression of CDKN2A. CCND1 encodes the cyclin D1 protein, which together with other cyclins, acts in the regulation of cyclin-dependent kinases (CDKs).