The precursor forms a disulfide‐linked dimer in the endoplasmic reticulum, which is proteolytically cleaved at the RXXR sequence to produce the mature secreted cytokine GDF15.[29, 30, 31] ELISA assay showed that ovarian cancer cells with circMETTL6 overexpression or NONO knockdown secreted significantly less GDF15 compared to control cells (Figure 5F,G), indicating that circMETTL6 and NONO cooperatively regulate the expression of GDF15. Here, GDF15 is linked to ovarian carcinoma.