Release of specific protease during mitotic cycle of L5178Y murine leukaemic cells by sublethal autolysis

Abstract

SUBLETHAL autolysis is postulated to be the process by which degradative enzymes may modify cell plasma membrane macromolecules without causing cell death^1,2. Malignant or virally transformed cells can be agglutinated by various agglutinins; their untransformed counterparts are not agglutinated, but normal cells become agglutinable upon mild treatment of the cells with a proteolytic enzyme³. Therefore, elevated levels of degradative enzymes may be important for maintenance of the malignant or transformed state through sublethal autolysis, which constantly modifies cell plasma membrane surfaces. This report shows that L5178Y cells release small amounts of a protease active at pH 7.8 and that release of this enzyme is almost exclusively in the M period of the L5178Y mitotic cycle. Rubin⁴ reported that small amounts of trypsin or Pronase produced an overgrowth phenomenon in cells; that is, contact-inhibited cells were released from contact inhibition and proceeded through a subsequent round of mitosis. Rubin⁴ has also isolated from cells infected with Rous sarcoma virus a similar non-dialysable, thermolabile overgrowth-stimulating factor.