PCNA and obstructive sleep apnea syndrome: The three OSA cell lines showed downregulated gene expression of CDKN2A (which encodes p16INK4a), CDKN2B, THBS1, PTHLH, CDKN1A, CCND1 and CCND3 and upregulated expression of CXCR4, BIRC5, RAD51, CDKN2C, BCL2, BRCA1, PCNA and CHEK2.