To prove whether CCND1 participated in NAP1L1/HDGF/c-Jun signal-induced cell proliferation, HDGF or c-Jun cDNA plasmid was transfected into shNAP1L1-treated breast cancer cells, and it was found that the c-Jun/CCND1 expression level was significantly upregulated in shNAP1L1-treated breast cancer cells. This evidence concerns the gene JUN and breast cancer.