Tumour suppressor protein p53 released by nuclease digestion increases at the onset of rat liver regeneration

Background/Aims: Protein kinase CK2 (CK2) increases when cells are committe d to proliferate, as in liver regeneration, This enzyme phosphorylates the tumour suppressor protein p53, whose expression controls the levels of many other cell cycle proteins. The aim of this study was to determine if CK2 w as affected by p53. Methods: Male Sprague-Dawley rats (200-250 g) were subjected to either part ial hepatectomy or laparotomy and the levels and subcellular distribution o f p53 were studied, following the approach used earlier for CK2. The levels of both proteins were also studied in the human cell lines HL-60 (devoid o f p53) and HepG2 (with normal p53 levels) and in fibroblasts from transgeni c p53-deficient mice (p53-/-) or homozygous for wild-type p53 (p53+/+), Com puter-assisted search was used to detect p53 consensus sequences in genes f or CK2 submits, Binding of p53 protein to some of these sequences was assay ed by electrophoretic mobility shift assay. Results: Rat liver p53 protein was present mainly in the fraction extracted from intact nuclei by nucleases (S1) and showed a transient increase, at 6 h post partial hepatectomy, as observed previously with nuclear CK2, The h uman CK2 alpha gene presents the consensus sequence for trans-activation by p53 and specific binding of p53 protein to some of these sequences was det ected in vitro. Total CR2 alpha was higher in HepG2 than in HL-60 cells but total CK2 and its cytosolic/ nuclear distribution was similar in mice (p53 +/+) fibroblasts and (p53-/-) fibroblasts. Conclusions: p53 is present in the nuclease-extracted S1 fraction from live r cells, as described for CK2, and undergoes similar changes at the beginni ng of rat liver regeneration. However, the data on cultured cells suggest t hat the expression of CK2 and its subcellular localization are p53-independ ent events.