ABSTRACT
OBJECTIVE: Enamelysin (MMP20) and kallikrein 4 (KLK4) are believed to be necessary to clear proteins from the enamel matrix of developing teeth. MMP20 is expressed by secretory stage ameloblasts, while KLK4 is expressed from the transition stage throughout the maturation stage. The aim of this study is to investigate the activation of KLK4 by MMP20 and the inactivation of MMP20 by KLK4. DESIGN: Native pig MMP20 (pMMP20) and KLK4 (pKLK4) were isolated directly from enamel scrapings from developing molars. Recombinant human proKLK4 (rh-proKLK4) was activated by incubation with pMMP20 or recombinant human MMP20 (rhMMP20), and the resulting KLK4 activity was detected by zymography. Reaction products were isolated by reverse-phase high performance liquid chromatography (RP-HPLC), and their N-termini characterized by Edman degradation. The pMMP20 was incubated with pKLK4 under mildly acidic or under physiologic conditions, and enzyme activity was analyzed by zymography. The catalytic domain of rhMMP20 was incubated with pKLK4 or recombinant human KLK4 (rhKLK4) and the digestion products were characterized by zymography and Edman degradation. RESULTS: Both pMMP20 and rhMMP20 activated rh-proKLK4 by cleaving at the propeptide-enzyme junction used in vivo. The pMMP20 was inactivated by pKLK4 under physiologic conditions, but not under mildly acidic conditions. Both pKLK4 and rhKLK4 cleaved MMP20 principally at two sites in the catalytic domain of MMP20. CONCLUSIONS: MMP20 activates proKLK4 and KLK4 inactivates MMP20 in vitro, and these actions are likely to occur during enamel formation in vivo.
