MMP1 and breast cancer: In addition, GSEA revealed that c-Fos (FOS gene-encoded protein) target genes, including lipid metabolism-related genes, such as MMP1, LIF, CAMK2A and LEPR, were significantly overexpressed in NR4A1-knockout BC cells compared with parental control cells (Fig. 5c), which were validated by RT-qPCR in luminal, basal-like and HER2-positive BC cells (Supplementary Fig. 5a, b).