Previous studies have highlighted the role of TGF‐β1‐SMAD3 activation in FMT and subsequent PF progression.[30] SNX9 has been demonstrated to promote SMAD3 phosphorylation and nuclear translocation.[31] Therefore, we hypothesized that endocytic rCTSK facilitated SMAD3 activation through SNX9 for COL1A1 production. Here, SNX9 is linked to pemphigus foliaceus.