POLY-ADP-RIBOSYLATION STUDIES IN DIFFERENT CONTEXTS: CANCER, NEURODEGENERATION, AND INFECTION

Poly-ADP-ribosylation (PARylation) was discovered as a postranslational modification consisting on the addition of lineal or branched ADP-ribose chains called poly-ADP-ribose (PAR). PAR is synthetized by poly-ADP-ribose polymerases (PARPs): PARP-1, PARP-2 and tankyrases (TNKS-1 & TNKS-2). In turn, PAR is degraded mainly by poly-ADP-ribose glycohydrolase (PARG). PARP-1 and PARP-2 have similar structures and partially overlapping functions. The same happens with TNKS-1 and TNKS-2. PARP-1/2 inhibitor Olaparib reached FDA approval to treat BRCA-mutated cancer patients under the paradigm of synthetic lethality. However, not all BRCA-mutated patients benefit from Olaparib. Conversely, Olaparib shows benefits in some BRCA-wt patients. Our studies in cell cultures addressed these issues. Some cells were treated with the radiomimetic agent bleomycin together with combined drugs (including Olaparib) that block all known double strand break (DSB) repair pathways, with neither DSB accumulation nor viability loss; such cells might have an unknown or intertwined mechanism of DSB repair, which could explain why some BRCA-mut patients do not respond to Olaparib. In turn, in NMuMG cells, Olaparib blocked and partially reverted the epithelial to mesenchymal transition (EMT) induced by TGF-β, disclosing a previously unknown mechanism of action of the drug, which could, in theory, prevent or promote metastases depending on the tumor state at the time of Olaparib administration. We are currently studying PAR metabolism changes in alternative EMT models and colon cancer tissue. PAR increase occurs in several neurodegenerative pathologies, but the research focus has usually been on nuclear PAR. Charcot-Marie-Tooth is a neurodegenerative disease triggered by demyelination, modelled by Trembler J mice. Schwann cells that form the peripheric myelin sheet harbor self-adherens junctions (AJ) to fix successive myelin layers. Similar to epithelial cells, AJ bear PAR where microfilaments are anchored. Moreover, like in epithelial cells, actin microfilaments dynamics is accompanied by PAR dynamics. Trembler J mice harbor not only more actin microfilaments but also more cytoplasmic PAR than wt-mice. PAR homeostasis participates in the host cell response to Trypanosome cruzi (Tcruzi) infection. TNKS inhibitors hamper in vitro Tcruzi infection in VERO cells, through interference with β-catenin nuclear translocation and TNF-α (expression and secretion).