SMAD3 and ovarian cancer: To elucidate whether CAF activation is dependent upon canonical TGF-β signaling via TGF-β receptors (TGFBRs) and SMAD3, we pretreated the fibroblast cell lines with either the TGF-β type I receptor inhibitors, A83-01 or ALK5 inhibitor II’ or the SMAD3 inhibitor, SIS3, before stimulating the cells with ovarian cancer cell conditioned medium.