Frozen prostate cancer samples were sectioned onto slides. Cell nuclei were isolated in situ with ice-cold cytoskeleton buffer (CSK: 300 mM sucrose, 100 mM NaCl, 10 mM PIPES, 3 mM MgCL 2 , 1 mM EGTA and 0.5% Triton X-100) (28) . The slides were fixed by dipping in ice-cold methanol for 3 min, followed by ice-cold acetone. After air drying the slides, they were allowed to age for at least 1 week in ethanol.