RECK and neoplasm: Additional analysis of tumor cells for intracellular signaling affected by miRNA-21 revealed that reversion-inducing cysteine-rich protein with Kazal motifs (RECK), a matrix metalloproteinase (MMP) inhibitor, not only blocked the interaction with exosomal miR-21-5p but completely prevented activation of tumor cells when transfected into RECK knockout tumor cells in a mutant form (Zhou et al., 2024).