Immunofluorescence studies of stably-expressed wild-type PML and PML C/C-in U2OS and MCF7 cells. ( A) Endogenous APBs were detected in (i) U2OS PCI Neo STC6 and (ii) PCI Neo STC8 clones. APBs were detected in (iii) U2OS PML STC20 and (iv) PML STC21 clones which stably express wild-type PML. APBs were not formed with the stable expression of PML C/C- in (v) U2OS PML C/C- STC20 and (vi) PML C/C- STC22 clones. (vii) Graph depicting percentage of U2OS cells expressing APBs. (B) Novel detection of APBs in MCF7 cells stably expressing wild-type PML. APBs were not present in (i) MCF7 PCI Neo STC1 and (ii) STC4 clones. No APBs were detected in (iii) MCF7 PML STC7 clone but stably-expressed wild-type PML formed distinct foci that co-localized with TRF2 to form APBs in (iv) PML STC10 clone. PML C/C- did not form APBs when expressed stably in MCF7 cells, (v) PML C/C- STC7 and (vi) PML C/C- STC22. (vii) Graph depicting percentage of MCF7 cells expressing APBs. At least 100 cells were scored and the results were summarized from at least three independent experiments. Values represent the mean ± SD. Wild-type PML is HA-tagged while PML C/C- is FLAG-tagged. APBs are defined by the co-localisation of PML with TRF2 and are indicated by arrows. DAPI was used for visualisation of the nucleus and the indicated antibodies were used. Images were captured with confocal microscopy at 100 X magnification. * indicates p < 0.05.