Poly(adenosine diphosphate-ribosylation) of nuclear matrix proteins in alkylating agent resistant and sensitive cell lines

Association of poly(ADP-ribose) polymerase with the nuclear matrix: the role of intermolecular disulfide bond formation, RNA retention, and cell type

The recovery of the enzyme poly(ADP-ribose) polymerase (pADPRp) in the nuclease- and 1.6 M NaCl-resistant nuclear subfraction prepared from a number of different sources was assessed by Western blotting. When rat liver nuclei were treated with DNase I and RNase A followed by 1.6 M NaCl, approximately 10% of the nuclear pADPRp was recovered in the sedimentable fraction. The proportion of pADPRp recovered with the residual fraction decreased to less than 5% of the total nuclear polymerase when nuclei were prepared in the presence of the sulfhydryl blocking reagent iodoacetamide and increased to approximately 50% of the total nuclear pADPRp when nuclei were treated with the sulfhydryl cross-linking reagent sodium tetrathionate (NaTT) prior to fractionation. To determine whether this effect of disulfide bond formation was unique to rat liver nuclei, nuclear matrix/cytoskeleton structures were prepared in situ by sequentially treating monolayers of tissue culture cells with Nonidet-P40, DNase I and RNase A, and 1.6 M NaCl (S.H. Kaufmann and J.H. Shaper (1991) Exp. Cell Res. 192, 511-523). When nuclear monolayers were prepared from HTC rat hepatoma cells, CaLu-1 human lung carcinoma cells, and CHO hamster ovary cells in the absence of NaTT, pADPRp was undetectable in the nuclease- and 1.6 M NaCl-resistant fraction. In contrast, when nuclear monolayers were isolated in the presence of NaTT, from 5% (CaLu-1) to 26% (HTC cells) of the total nuclear pADPRp was recovered with the nuclease- and salt-resistant fraction. Examination of these residual structures by SDS-polyacrylamide gel electrophoresis under nonreducing conditions suggested that pADPRp was present as a component of disulfide cross-linked complexes. Further analysis by immunofluorescence revealed that the pADPRp was diffusely distributed throughout the CaLu-1 or CHO nuclear matrix. In addition, when matrices were prepared in the absence of RNase A, pADPRp was also observed in the residual nucleoli. These observations reveal that the recovery of pADPRp with a nuclease- and salt-resistant nuclear subfraction is dependent on the source of the nuclei and on the conditions used to fractionate those nuclei. In addition, these observations raise the possibility that there might be different functional classes of pADPRp molecules within the nucleus.

Poly(ADP-ribose) metabolism in proliferating versus quiescent cells and its relationship to their radiation responses

In the murine tumour cell lines 66 and 67 growing in vitro, quiescent (Q; unfed plateau-phase) cells are more sensitive to X-ray-induced cell killing than are proliferating (P) cells, while St4 cells (Q cells that have been re-fed and returned to 37 degrees C for 4h) are similar to P cells in radiosensitivity. We have been investigating parameters of poly(ADP-ribose) metabolism in order to determine whether such factors contribute to the variations in radiosensitivity of these growth states. These parameters were cellular NAD content, the activity of poly(ADP-ribose) transferase (ADPRT) in permeabilized cells and the activity of poly(ADP-ribose)-degrading enzymes. The results suggest that in line 66, but not 67, a reduced ability to regenerate NAD following irradiation was associated with the reduced survival of Q cells. However, neither the baseline activity of ADPRT nor the degree of stimulation of ADPRT by X-rays was found to correlate with survival, or with the induction and repair of DNA strand breaks. Stimulation of ADPRT by X-rays was dependent on dose and was greatest for a 2-min incubation with 3H-NAD. For a 2-min incubation the stimulation of ADPRT following a dose of 50 Gy was 7- and 10-fold in 66 and 67 P cells, respectively, versus 3-4-fold in Q cells. Detectable stimulation was observed in 66 P and Q cells for doses as low as 5 Gy. P and Q cells did not differ in the rate of degradation of the poly(ADP-ribose) polymers.