Distinct from the extracellular effect of CALU-1/− 2 in downregulated cancers [31], CALU-15 facilitated the nuclear expression of nucleus GDF-15, which then mainly promoted cell migration and tumour metastasis [33]; our study confirmed that CALU promoted the expression of GDF-15 (Additional file 1: Figure S2). The gene discussed is CALU; the disease is cancer.