Freezing induces artificial cleavage of apoptosis-related proteins in human bone marrow cells

The aim of this study was to investigate whether freeze-thawing of freshly isolated human mononuclear bone marrow cells (MNC) influences the integrity of apoptosis-related proteins as determined by immunoblot analyses. Our results show that bone marrow is more sensitive to this process than either myelomonocytoid leukemic P39 or Jurkat T-lymphocyte cell lines. Specifically, bone marrow cells displayed a high level of intrinsic proteolytic activity in response to a single freeze-thaw cycle, which led to the cleavage of various proteins involved in apoptosis cell signaling. This effect was completely blocked by the inclusion of broad-spectrum protease inhibitors in the freezing medium and subsequently thawing the cells on ice. Since differences in the freezing conditions (- 80 degreesC vs, liquid nitrogen) did not alter the proteins of interest, we suggest that the thawing process is the critical point when proteolytic enzyme activity is elevated. (C) 2000 Elsevier Science B.V. All rights reserved.