87P WIP1 phosphatase promotes etoposide induced autophagy in medulloblastoma and neuroblastoma

Wip1/PPM1D is a serin/threonine phosphatase which is involved in timely termination of DNA damage response. Overexpression of Wip1 is commonly seen in human solid cancers including neuroblastoma and medulloblastoma that displays oncogenic features. Oncogenic Wip1 negatively regulates tumor suppressor responses such as apoptosis or senescence. Autophagy plays a tumor suppressor role by removing damaged organelles/proteins and limiting cell growth and genomic instability in cancer cells. The molecular mechanisms underlying autophagy's tumor-promoting activities are largely unknown Here, we investigated the role of oncogenic Wip1 phospahates in regulation of autophagy in neuroblastoma and medulloblastoma. D283-med and IMR32 cells are grown according to ATTC protocol. Autophagy was stimulated with etoposide and inhibited with chloroquine. GSK2830371 is used to target Wip1. Autophagy markers are tested with WB analysis and with confocal microscopy analysis of LC3 I/II puncta formation. Vacuolazion was measured by quinacrine staining. Wip1-Ulk1 interaction was investigated via co-IP and co-localization analysis. BrDU/PI and Annexin V/7AAD assays were used to examine the cell cycle and apoptosis, respectively. In neuroblastoma and medulloblastoma cells, oncogenic Wip1 promotes etoposid induced autophagy and improves cancer cell survival. Wip1 phosphatase interacts with and dephosphorylates Ulk1 during etoposide induced autophagy which is associated with elevated p53 levels. Suppression of Wip1 and/or autophagy prevents degredation of pro-apoptotic proteins thus results in promotion of apoptosis. Furthermore, inhibition of Wip1 and autophagy reduce cancer cells ability to colonize in vitro. Oncogenic Wip1 play a key role in enhancing etoposide induced autophagy by dephosphorylating ULK1 and contributes to cancer cell survival. Wip1 mediated autophagy may be a promising therapeutic target for improvment of chemotherapy response.