Establishment of association of an Mg²⁺‐dependent endonuclease with the rat liver nuclear matrix in cryonecrosis

Abstract

Previously, we characterized the endonucleolytic activity of the nuclear matrix prepared from rat liver cryopreserved in liquid nitrogen. The enzymic activity was attributed to a 23 kDa, Mg(2+)-dependent and sequence non-specific endonuclease (p23) stably associated with the nuclear matrix. Here we show that p23 was absent from the nuclear matrix prepared from fresh liver. Instead, both ex vivo (cryopreservation), as well as in vivo-induced necrosis by repeated freezing/thawing of liver tissue in an anaesthetized rat, promoted the activation and translocation of p23 to the nuclear matrix. Considering that ex vivo and in vivo freezing/thawing of the liver were accompanied by morphological (nuclear compaction) and biochemical events (increased LDH activity, disorderly genomic DNA degradation, absence of lamin proteolysis, appearance of 62 and 50 kDa necrotic cleavage products of PARP-1) commonly observed during necrosis, and because the association of p23 with the nuclear matrix was saturable, reflecting the existence of a limited number of distinct high affinity sites on the nuclear matrix for p23, we concluded that the activation of the nuclear matrix-associated endonuclease p23 is a feature of liver cryonecrosis. Although cryonecrosis represents a typical example of acute cell damage, our results suggest that it is realized by ordered molecular events.