CDKN1A and breast cancer: For instance, knockdown of CRY2 in MCF-7 cells increased accumulation of mutagen-induced DNA damage and altered expression of genes involved in the DNA damage response and cell cycle regulatory pathways including cyclin-dependent kinase inhibitor p21 (CDKN1A) and induction of cyclin D1 (CCND1)—an oncogene that is often overexpressed in breast cancer cases [45].