Kallikrein-related peptidase 6 can cleave human-muscle-type 6-phosphofructo-1-kinase into highly active shorter fragments.

PURPOSE: Cancer cells consume more glucose than normal human cells and convert most glucose into lactate. It has been proposed that deregulated glycolysis is triggered by the posttranslational modification of 85 kDa muscle-type 6-phosphofructo-1-kinase (PFK-M) which is cleaved by a specific protease to form shorter, highly active, feedback-inhibition-resistant PFK-M fragments.

PRINCIPAL RESULTS: To find the protease involved in PFK-M modification, analyses of the protease target sites on the human PFK-M enzyme yielding 45-47 kDa fragments were performed in silico. The results suggested that an enzyme in the kallikrein (KLK) family may be involved. Kallikreins can be self-activated in the cytosol and are often overexpressed in cancer cells. After incubating the internally quenched FRET peptide with a sequence characteristic of the target site, along with the active KLK6, the cleavage of the peptide was observed. The ability of KLK6 to cleave native PFK-M and form highly active citrate-resistant 45 kDa fragments was further confirmed by enzymatic tests and SDS-PAGE. A role of KLK6 in the posttranslational modification of native PFK-M was ultimately confirmed in vivo. A yeast strain that encoded native human PFK-M as the only PFK1 enzyme was additionally transformed with proKLK6 or KLK6 genes under the control of an inducible promoter. The transformants growth rate was found to increase after the induction of proKLK6 gene expression as compared to the strain with the native PFK-M enzyme.

CONCLUSION: KLK6 may be the key protease involved in the modification of PFK-M and trigger deregulated glycolytic flux in cancer cells.