Conversion of cathepsin E to enzymatic unstable form in gastric cancer cells

A new acid proteinase in human gastric cancer, named medium moving proteinase (Med.P), was found also in a gastric cancer transplanted into nude mouse. However, Med.P disappeared when the samples prepared from gastric cancer tissues were left for over 4 weeks at -80 degrees C, whereas the activity of cathepsin E (CE) increased. When these samples were reduced by dithiothreitol (DTT), Med.P appeared again and the CE activity decreased. These phenomena, revealed by electrophoretic analyses, indicated that Med.P is a monomeric form of CE (mono-CE). At weakly alkaline pH and after heating, mono-CE appeared to be more unstable than CE. These results indicated that CE assume an enzymatically unstable monomeric form in cancer cells.