RSPO2 and hepatocellular carcinoma: In RSPO2-responsive32 human hepatocellular carcinoma HEPG2 cells, among RSPO1-4, only RSPO2 decreased FGF19-mediated ERK phosphorylation (Supplementary Fig. 2a, b), while all RSPOs similarly potentiated Wnt signaling (Supplementary Fig. 2c).