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Loss of ephrin B2 receptor (EPHB2) sets lipid rheostat by regulating proteins DGAT1 and ATGL inducing lipid droplet storage in prostate cancer cells

Abstract

Lipid droplet (LD) accumulation in cancer results from aberrant metabolic reprograming due to increased lipid uptake, diminished lipolysis and/or de novo lipid synthesis. Initially implicated in storage and lipid trafficking in adipocytes, LDs are more recently recognized to fuel key functions associated with carcinogenesis and progression of several cancers, including prostate cancer (PCa). However, the mechanisms controlling LD accumulation in cancer are largely unknown. EPHB2, a tyrosine kinase (TKR) ephrin receptor has been proposed to have tumor suppressor functions in PCa, although the mechanisms responsible for these effects are unclear. Given that dysregulation in TRK signaling can result in glutaminolysis we postulated that EPHB2 might have potential effects on lipid metabolism. Knockdown strategies for EPHB2 were performed in prostate cancer cells to analyze the impact on the net lipid balance, proliferation, triacylglycerol-regulating proteins, effect on LD biogenesis, and intracellular localization of LDs. We found that EPHB2 protein expression in a panel of human-derived prostate cancer cell lines was inversely associated with in vivo cell aggressiveness. EPHB2 silencing increased the proliferation of prostate cancer cells and concurrently induced de novo LD accumulation in both cytoplasmic and nuclear compartments as well as a “shift” on LD size distribution in newly formed lipid-rich organelles. Lipid challenge using oleic acid exacerbated the effects on the LD phenotype. Loss of EPHB2 directly regulated key proteins involved in maintaining lipid homeostasis including, increasing lipogenic DGAT1, DGAT2 and PLIN2 and decreasing lipolytic ATGL and PEDF. A DGAT1-specific inhibitor abrogated LD accumulation and proliferative effects induced by EPHB2 loss. In conclusion, we highlight a new anti-tumor function of EPHB2 in lipid metabolism through regulation of DGAT1 and ATGL in prostate cancer. Blockade of DGAT1 in EPHB2-deficient tumors appears to be effective in restoring the lipid balance and reducing tumor growth.

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Fig. 1: EPHB2 silencing induces prostate cancer cell proliferation.
Fig. 2: Loss of EPHB2 increases lipid storage in prostate cells.
Fig. 3: EPHB2 loss induces lipid droplet accumulation in prostate cancer cells.
Fig. 4: EPHB2 loss favors lipogenesis.
Fig. 5: DGAT1 inhibition reverses EPHB2 loss lipid-induced changes.
Fig. 6: Lipid metabolic alterations induced by EPHB2 deficiency in prostate cancer.

Data availability

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

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Acknowledgements

We want to thank Yana Filipovich for helping us with the culture of cell lines used in this project and Nicholas Mehta for his help with western blot.

Funding

This work was supported by the US National Institutes of Health/National Cancer Institute (RO1 CA24920), Department of Defense (PC190755) and the Rob Brooks Fund for Personalized Cancer Care.

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OF and SC perform study concept and design. AM, FN performed cell culture and western blot experiments, MG provided acquisition and analysis of LD data, VG performed immunofluorescence experiments. OF and AM performed writing and paper preparation, SC and SH performed evaluation of experiments and review of the paper prior submission. All authors read and approved the final paper.

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Correspondence to Omar E. Franco.

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Morales, A., Greenberg, M., Nardi, F. et al. Loss of ephrin B2 receptor (EPHB2) sets lipid rheostat by regulating proteins DGAT1 and ATGL inducing lipid droplet storage in prostate cancer cells. Lab Invest (2021). https://doi.org/10.1038/s41374-021-00583-9

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