Yang X, Stennicke H R, Wang B, Green D R, Jänicke R U, Srinivasan A, Seth P, Salvesen G S, Froelich C J
Evanston Northwestern Healthcare Research Institute, Evanston, Illinois 60201, USA.
J Biol Chem. 1998 Dec 18;273(51):34278-83. doi: 10.1074/jbc.273.51.34278.
Granzyme B (GrB) is predicted to trigger apoptosis by activating preferred caspases, but the zymogens that are directly processed by the granzyme and the requirements for these interactions remain unclarified. We examined this dilemma by comparing the kinetics and pattern of GrB-mediated activation of the executioner caspase-7 in vitro and in vivo. GrB rapidly activates procaspase-7 in vitro by cleaving between the large and small subunits leaving the propeptide intact. During GrB-mediated apoptosis, the caspase-7 propeptide is removed and cleavage occurs between the subunits. Strikingly, caspase-7 is unprocessed in caspase-3-deficient MCF-7 cells exposed to GrB but is rapidly activated when the cells are solubilized. Transfection with caspase-3 restores the removal of the caspase-7 propeptide and the capacity of GrB to subsequently activate the caspase. The data suggest that GrB activates caspase-3, which then removes the propeptide of caspase-7 allowing activation by GrB. Thus GrB initiates the death pathway by processing the accessible caspase-3, and the caspase-7 propeptide regulates trans-activation of the zymogen by granzyme. As a consequence, two proteases, caspase-3 and GrB, are required to activate procaspase-7.
颗粒酶B（GrB）被预测通过激活特定的半胱天冬酶来触发细胞凋亡，但颗粒酶直接作用的酶原以及这些相互作用的条件仍不明确。我们通过比较体外和体内GrB介导的执行者半胱天冬酶-7激活的动力学和模式来研究这一困境。在体外，GrB通过在大亚基和小亚基之间切割，使前肽保持完整，从而迅速激活半胱天冬酶原-7。在GrB介导的细胞凋亡过程中，半胱天冬酶-7的前肽被去除，且在亚基之间发生切割。引人注目的是，在暴露于GrB的半胱天冬酶-3缺陷型MCF-7细胞中，半胱天冬酶-7未被加工，但当细胞溶解时会迅速被激活。转染半胱天冬酶-3可恢复半胱天冬酶-7前肽的去除以及GrB随后激活半胱天冬酶的能力。数据表明，GrB激活半胱天冬酶-3，然后半胱天冬酶-3去除半胱天冬酶-7的前肽，从而使GrB能够激活半胱天冬酶。因此，GrB通过加工可及的半胱天冬酶-3启动死亡途径，并且半胱天冬酶-7前肽调节颗粒酶对酶原的反式激活。结果，激活半胱天冬酶原-7需要两种蛋白酶，即半胱天冬酶-3和GrB。
