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Inhibition of phosphodiesterase 4D suppresses mTORC1 signaling and pancreatic cancer growth
Mi-Hyeon Jeong, … , Zhikai Chi, Jenna L. Jewell
Mi-Hyeon Jeong, … , Zhikai Chi, Jenna L. Jewell
Published July 10, 2023
Citation Information: JCI Insight. 2023;8(13):e158098. https://doi.org/10.1172/jci.insight.158098.
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Research Article Cell biology

Inhibition of phosphodiesterase 4D suppresses mTORC1 signaling and pancreatic cancer growth

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Abstract

The mammalian target of rapamycin complex 1 (mTORC1) senses multiple upstream stimuli to orchestrate anabolic and catabolic events that regulate cell growth and metabolism. Hyperactivation of mTORC1 signaling is observed in multiple human diseases; thus, pathways that suppress mTORC1 signaling may help to identify new therapeutic targets. Here, we report that phosphodiesterase 4D (PDE4D) promotes pancreatic cancer tumor growth by increasing mTORC1 signaling. GPCRs paired to Gαs proteins activate adenylyl cyclase, which in turn elevates levels of 3′,5′-cyclic adenosine monophosphate (cAMP), whereas PDEs catalyze the hydrolysis of cAMP to 5′-AMP. PDE4D forms a complex with mTORC1 and is required for mTORC1 lysosomal localization and activation. Inhibition of PDE4D and the elevation of cAMP levels block mTORC1 signaling via Raptor phosphorylation. Moreover, pancreatic cancer exhibits an upregulation of PDE4D expression, and high PDE4D levels predict the poor overall survival of patients with pancreatic cancer. Importantly, FDA-approved PDE4 inhibitors repress pancreatic cancer cell tumor growth in vivo by suppressing mTORC1 signaling. Our results identify PDE4D as an important activator of mTORC1 and suggest that targeting PDE4 with FDA-approved inhibitors may be beneficial for the treatment of human diseases with hyperactivated mTORC1 signaling.

Authors

Mi-Hyeon Jeong, Greg Urquhart, Cheryl Lewis, Zhikai Chi, Jenna L. Jewell

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Figure 2

PDE4D promotes mTORC1 activity through Raptor Ser791 phosphorylation.

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PDE4D promotes mTORC1 activity through Raptor Ser791 phosphorylation.
(A...
(A and B) PDE4D inhibits Raptor Ser791 phosphorylation. (A) HA-tagged Raptor was coexpressed with FLAG-tagged PDE4D4 in HEK293A cells for 48 hours; cells were then treated with forskolin (10 μM) for 1 hour. Lysates were immunoprecipitated (IP) with anti-HA antibody and immunoblotted with anti-pPKA substrate (RRXS/T) antibody. (B) Same as A but with FLAG-tagged PDE4D6. (C) PDE4D controls Raptor Ser791 phosphorylation. FLAG-tagged PDE4D (WT), FLAG-tagged PDE4D catalytically inactive mutant (D620A), and HA-tagged Raptor were overexpressed. Cells were treated with forskolin (10 μM) for 1 hour. Lysates were immunoprecipitated with anti-HA antibody and immunoblotted with anti-pPKA substrate antibody. (D) PDE4D depletion enhances Raptor Ser791 phosphorylation. Cells with PDE4D shRNA were stimulated with forskolin (10 μM) for 1 hour. Lysates were immunoprecipitated with anti-Raptor antibody and immunoblotted for pPKA substrate. Arrow indicates PDE4D. (E) Chemical inhibition of PDE4D decreases mTORC1 activity. HEK293A cells were stimulated with rolipram, roflumilast, and GEBR-7b for 2 hours and mTORC1 activity was analyzed. (F and G) Raptor Ser791 phosphorylation controls mTORC1 activity. (F) HEK293A cells expressing FLAG-tagged Raptor (WT) or FLAG-tagged Raptor S791A (phospho-defective) were treated with or without GEBR-7b (20 μg/mL) for 2 hours. mTORC1 activity was analyzed. (G) HA-tagged Raptor (WT) or HA-tagged Raptor S791A (phospho-defective) was overexpressed in PDE4D-depleted cells (shPDE4D). mTORC1 activity was analyzed. (H) PDE4D controls mTORC1 activity. Cells were transfected with FLAG-tagged PDE4D4 for 48 hours and stimulated with roflumilast (50 μM) for 2 hours. mTORC1 activity was analyzed. (I and J) Pharmacologic inhibition of PDE4D enhances Raptor Ser791 phosphorylation. HEK293A cells were pretreated with either roflumilast (50 μM) (I) or GEBR-7b (20 μg/m) (J) for 1 hour and then treated with forskolin (10 μM) for 1 hour. Lysates were immunoprecipitated with anti-Raptor antibody and Raptor Ser791 phosphorylation was assessed. Immunoblots probed for Raptor, pCREB, CREB, FLAG, HA, S6K1, and β-actin are controls. WCL, whole-cell lysates.

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