BACKGROUND
Pancreatic cancer has the highest prevalence of cancer-associated cachexia among all cancers. ZIP4 promotes pancreatic cancer progression by regulating oncogenic miR-373, and perturbation of circular RNAs (circRNAs) is associated with cancer aggressiveness. This study aims to identify circRNAs involved in ZIP4/miR-373 driven cancer growth and cachexia and decipher the underlying mechanism.
METHODS
Differentially expressed circRNAs and potential targets of miRNA were identified through in silico analysis. The RNA interactions were determined by biotinylated miRNA pulldown, RNA immunoprecipitation, and luciferase reporter assays. The function of circRNA in ZIP4/miR-373 signaling axis were examined in human pancreatic cancer cells, 3D spheroids and organoids, mouse models, and clinical specimens. Mouse skeletal muscles were analyzed by histology.
RESULTS
We identified circANAPC7 as a sponge for miR-373, which inhibited tumor growth and muscle wasting in vitro and in vivo. Mechanistic studies showed that PHLPP2 is a downstream target of ZIP4/miR-373. CircANAPC7 functions through PHLPP2 mediated dephosphorylation of AKT, thus suppressing cancer cell proliferation by downregulating Cyclin D1 and inhibiting muscle wasting via decreasing the secretion of TGF-β through STAT5. We further demonstrated that PHLPP2 induced dephosphorylation of CREB, a zinc-dependent transcription factor activated by ZIP4, thereby forming a CREB/miR-373/PHLPP2 feed-forward loop to regulate tumor progression and cancer cachexia.
CONCLUSION
This study identified circANAPC7 as a novel tumor suppressor, which functions through the CREB/miR-373/PHLPP2 axis, leading to AKT dephosphorylation, and Cyclin D1 and TGF-β downregulation to suppress tumor growth and muscle wasting in pancreatic cancer.