RESUMO
Cohesin is a protein complex consisting of four core subunits responsible for sister chromatid cohesion in mitosis and meiosis, and for 3D genome organization and gene expression through the establishment of long distance interactions regulating transcriptional activity in the interphase. Both roles are important for telomere integrity, but the role of cohesin in telomere maintenance mechanisms in highly replicating cancer cells in vivo is poorly studied. Here we used a zebrafish model of brain tumor, which uses alternative lengthening of telomeres (ALT) as primary telomere maintenance mechanism to test whether haploinsufficiency for Rad21, a member of the cohesin ring, affects ALT development. We found that a reduction in Rad21 levels prevents ALT-associated phenotypes in zebrafish brain tumors and triggers an increase in tert expression. Despite the rescue of ALT phenotypes, tumor cells in rad21+/- fish exhibit an increase in DNA damage foci, probably due to a reduction in double-strand breaks repair efficiency.
Assuntos
Neoplasias Encefálicas/genética , Proteínas de Ligação a DNA/genética , Haploinsuficiência/genética , Telômero/genética , Peixe-Zebra/genética , Animais , Proteínas de Ciclo Celular/genética , Linhagem Celular Tumoral , Proteínas Cromossômicas não Histona/genética , Quebras de DNA de Cadeia Dupla , Reparo do DNA/genética , Células HeLa , Humanos , Fenótipo , CoesinasRESUMO
Besides its canonical role in stabilizing telomeres, telomerase reverse transcriptase (TERT) may promote tumor growth/progression through extra-telomeric functions. Our previous in vitro studies demonstrated that short-term TERT inhibition by BIBR1532 (BIBR), an inhibitor of TERT catalytic activity, negatively impacts cell proliferation and viability via telomeres' length-independent mechanism. Here we evaluate the anti-proliferative and pro-apoptotic effects of short-term telomerase inhibition in vivo in wild-type (wt) and tert mutant (terthu3430/hu3430; tert-/-) zebrafish embryos, and in malignant human B cells xenografted in casper zebrafish embryos. Short-term Tert inhibition by BIBR in wt embryos reduced cell proliferation, induced an accumulation of cells in S-phase and ultimately led to apoptosis associated with the activation of DNA damage response; all these effects were unrelated to telomere shortening/dysfunction. BIBR treatment showed no effects in tert-/- embryos. Xenografted untreated malignant B cells proliferated in zebrafish embryos, while BIBR pretreated cells constantly decreased and were significantly less than those in the controls from 24 to up to 72 h after xenotransplantation. Additionally, xenografted tumor cells, treated with BIBR prior- or post-transplantation, displayed a significant higher apoptotic rate compared to untreated control cells. In conclusion, our data demonstrate that short-term telomerase inhibition impairs proliferation and viability in vivo and in human malignant B cells xenografted in zebrafish, thus supporting therapeutic applications of TERT inhibitors in human malignancies.
