88P - PPM1D/WIP1 phosphatase mediates basal and genotoxic stress-induced autophagy via ULK-1 de-phosphorylation

Background

PPM1D/WIP1 is a Ser/Thr phosphatase activated upon genotoxic stress in a p53 dependent manner and involved in regulation of DNA damage response (DDR) . Wip1 is amplified and over expressed in common human cancers and thus exerts oncogenic functions. Oncogenic Wip1 negatively regulates cellular responses to chemotherpy such as apoptosis and senescence. Here, we aimed to investigate the role of oncogenic Wip1 in induction of basal autophagy and chemotherpy mediated autophagy in breast cancer cells.

Methods

Etoposide was used to induce autophagy and Chloroquin (CQ) for inhibition. GSK2830371 was used to inhibit Wip1. LC3I/II conversion P62 degradation, total and phosphorylated (Ulk1 p-Ser757) levels were by analysed WB. Wip1-Ulk1 interaction was demonstrated by co-IP analysis. LC3 puncta formation was analysed by and immunofluorescence staining. Apoptosis, cell cycle, and senescence were measured by AnnexinV/7AAD, BrdU/PI analysis and SAβ-gal staining, respectively Colony formation assay was used to assess cells ability to colonize.

Results

Utilizing Wip1 over expressing MCF-7 cells, here we showed that oncogenic Wip1 increased basal autophagy and mediated etoposide-induced autophagy as confirmed by accumulation of LC3-II, degradation of p62, and formation of LC3II puncta. Inhibition of Wip1 increased phosphorylation of Ulk1 from Ser757 both in basal and etoposide induced autophagy. Further, endogenous Wip1 co-precipitated with Wip1 during basal and etoposide induced autophagy. Inhibition of autophagy or Wip1 enhanced apoptosis in response to etoposide but not senescence.

Conclusions

In conclusion our data suggest that oncogenic Wip1 may increase basal autophagy to support the survival of cancer cells. In addition Wip1 dependent autophagy in response to chemotherpy agents may cause resistance to chemotherapy. Thus targeting of Wip1-Ulk1 may lead enhancement of the chemotherapy response as a promising therapetic strategy.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

M.K. Kilic Eren.

Funding

This work is supported by TUBITAK Gr.N . 119S135.

Disclosure

All authors have declared no conflicts of interest.