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DNase activity in kidney cell pyknosis induced by serum deprivation

Pyknosis (nuclear shrinkage) is an important feature of apoptosis, which is preceded by activation of apoptotic pathways and is followed by karyorrhexis (nuclear fragmentation). The mechanism of pyknosis remains a mystery. The goals of this study were to determine if nuclear membrane ruptures when DNA fragmentation starts during pyknosis and to determine the involvement of DNases, cellular compartments, and chaperone proteins in pyknosis. A novel florescent probe to measure DNase activity was used in live kidney tubular epithelial NRK‐52E cells. Pyknosis was induced by serum‐deprivation; DNA breaks were measured by TUNEL; and immunocytochemistry of nuclear membrane, DNases, cellular compartments and chaperones was applies to characterize potential mechanisms. We demonstrated that: (a) DNase activity asymmetrically concentrates on one side of the nucleus, which changes the shape of the nucleus; (b) DNA fragmentation occurs but; (c) nuclear membrane does not break during pyknosis; (d) no measurable DNases were observed in the nucleus; (e) DNase activity colocalized with Golgi, ER, vesicles and HSP60, all of which seem to contribute to the mechanism of pyknosis. NIH R01 DK078908 and VA Merit Review grants to AGB.