MMP3 and melanoma: The novel recombinant protein cytotoxin 2 derived from Naja naja oxiana inhibited the transforming growth factor/suppressor of mothers against the decapentaplegic (TGFβ/SMAD) signaling pathway, and the expression of matrix metalloproteinase 3 (MMP3) in the human melanoma cell line SK-MEL-03, without side effects on the normal fibroblast cell line HFF-2 [104].