Astragaloside IV directly targets PPP1R14B to sensitize prostate cancer to anti-PD-1 immunotherapy by remodeling the CX3CL1/CD8+ T cell axis

Abstract

Background: Resistance to immune checkpoint inhibitors (ICIs) in prostate cancer (PCa) is driven by a "cold" tumor immune microenvironment. Astragaloside IV (AS-IV), a major bioactive saponin isolated from Astragalus membranaceus, exhibits immunomodulatory potential, yet its direct molecular targets remain elusive. Concurrently, PPP1R14B is overexpressed in PCa, but its role in mediating immune evasion is unclear.

Purpose: To investigate whether AS-IV targets PPP1R14B to remodel the tumor immune microenvironment (TIME) and sensitize PCa to anti-PD-1 therapy.

Methods: The AS-IV/PPP1R14B interaction was validated using molecular docking, surface plasmon resonance (SPR), and cellular thermal shift assays (CETSA). Mechanisms were dissected via ubiquitination assays, ROS analysis, and T cell co-cultures. Antitumor efficacy was evaluated in syngeneic mouse models alone or with anti-PD-1.

Results: AS-IV bound PPP1R14B (K_D = 4.88 μM), inducing its ubiquitin-proteasomal degradation. This depletion inhibited Wnt/β-catenin signaling via regulation of the AKT/GSK-3β axis and induction of mitochondrial ROS. Consequently, AS-IV relieved CX3CL1 repression, promoting the recruitment and cytotoxic function of CD8⁺ T cells. In vivo, AS-IV synergized with anti-PD-1 to suppress tumor growth, an effect that was largely dependent on PPP1R14B downregulation.

Conclusion: AS-IV reverses immune exclusion by targeting PPP1R14B to suppress Wnt/β-catenin signaling. These findings identify the AS-IV/PPP1R14B/CX3CL1 axis as a mechanistic basis for using AS-IV to overcome ICI resistance in PCa.

Keywords: Astragaloside IV; CX3CL1; Immune exclusion; PPP1R14B; Prostate cancer; Wnt/β-catenin signaling.