A) mRNA levels of all nine proprotein convertases (PCs) were determined by qRT-PCR in 5 Ewing sarcoma, 8 osteosarcoma and 20 rhabdomyosarcoma (RMS) cell lines. Shown are levels relative to GAPDH expression. B) Protein levels of proform and mature furin were assessed by immunoblotting in 20 different RMS cell lines. C) Endogenous furin activity of selected RMS cell lines: Rh36, RD (eRMS), Rh3, Rh4, Rh30, Rh41 and RMS13 (aRMS). Furin activity deficient cells LoVo cells serve as negative control. Furin was captured from cell lysates on anti-furin antibody coated plates and furin activity was measured by addition of the fluorogenic substrate Boc-RVRR-AMC after 6h. Displayed are values normalized by background subtraction.