Repair and misrepair of telomeric DNA in dynamic interactions with PML nuclear bodies and lamin B1 in doxorubicin-treated cancer cells

Telomeres in epithelial tumors are maintained by telomerase; however, in the MDA-MB-231 breast cancer cell line, treated by doxorubicin (DOX), we found a transient suppression of the telomerase (TERT) before cell growth resumed. Accumulation of cells in late-S-G2/M, mitotic slippage, octaploidy, and decrease of lamin B1 (LMNB1) coincided with this response. The telomere clustering and ALT-like process marked by the telomere shelterin (TRF2) colocalised in PML bodies with DNA DSBs (γH2AX) and recombinase RAD51 were observed in 11-12% of cells. They were preset by arrays of PML-bodies juxta-colocalized with the foci of meiotic prophase proteins SPO11 and DMC1. On the 3rd week, the cells de-polyploidised and returned to the normal cycle, telomerase, and mitosis. ALT-like bodies were also found in BRAFV600E-SK-MEL-28 DOX-treated melanoma cells. However, after sublethal doses of DOX, the formation of PML dimeric rods flanked and tandemly joined by misrepaired TRF2/γH2AX foci occured. Such PML tracts, circumventing cell nuclei undergoing MOS-microtubule-driven rotation, interacted with peripheral chromatin and intermitted with LMNB1 fragments. Furthermore, LMNB1 massively left the nuclear periphery, forming intranuclear flows, and/or convoluted into large peri-nucleolar PML bodies. We interpret our observations as the attempts by damaged, senescing cancer cells to use several mechanisms exploiting PML isoforms and meiotic proteins for telomere repair.