Processing bodies (P-bodies) are cytoplasmic mRNA granules that form a hub to regulate mRNA translation via controlling decapping, degradation, and storage. P-bodies markedly increase as part of a stress response for example during nutrient deprivation and hypoxia. Thus, P-bodies could regulate cell fate by tuning protein levels during the stress, and thereby contribute to tumor initiation, growth, and metastasis. However, it is unclear how P-body formation is regulated by these stress and what biologic pathways P-body controls.

Dysregulation of PIM and AKT kinases has been found in multiple cancers, including prostate and breast cancers. We find that the protein Enhancer of mRNA-decapping Protein 3 (EDC3), a P-body component, binds with the PIM protein kinase and is phosphorylated on serine 161 by the PIM and AKT kinases, suggesting these kinases could regulate P-body formation and function. Thus, we hypothesize that these oncogenic kinases regulate the EDC3 activity and P-body function via the phosphorylation of EDC3. Suppression of EDC3 phosphorylation by inhibiting PIM and AKT activities with drugs leads to an increase in P-body number. A knock-in mutation substituting alanine for serine 161 in PC3-LN4 prostate cancer cell line inhibited growth, migration and invasion in vitro. Prostate cancer tumor growth in these cells containing EDC3 mutation was reduced in mouse xenograft model, suggesting that this single phosphorylation is essential for regulating cell growth. These results suggest that the level of specific RNAs and its translation is being controlled by this mutation. Indeed, integrin family proteins, ITGB1 and ITGA6, are shown to be decreased in these cells consistent with the inability of these cells to attach and invade. High levels of phosphorylated EDC3 were detected in the breast cancer cell lines tested, whereas non-transformed immortalized breast epithelial cell lines showed much lower EDC3 phosphorylation. IHC staining of human breast cancer samples with phospho-specific antibodies demonstrated that EDC3 was highly phosphorylated in contrast to normal breast tissue which demonstrated low level of phosphorylation. These data indicate that in tumors, breast and prostate cancer, with activated PIM and AKT, high phosphorylation of EDC3 would increase the translation of target mRNAs via reducing their storage and destruction and affecting tumor cell growth and motility. Therefore, the phosphorylation of EDC3 by Pim and AKT kinases can be a driver of malignancy by controlling mRNA levels in breast and prostate cancers.

Citation Format: Jeremiah Bearss, Sathish K. Padi, Neha Singh, Marina Cardo-Vila, Andrew S. Kraft, Koichi Okumura. Regulation of P-body dynamics and formation in tumors through EDC3 phosphorylation by PIM and AKT [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2296.