Abstract SPRED2 (Sprouty-related, EVH1 domain-containing protein 2) is a negative regulator of Ras-dependent ERK1/2 signaling. Our previous studies revealed that SPRED2 suppresses hepatocellular carcinoma (HCC) progression by limiting cancer stemness through a SPRED2/p53/miR-506-3p/KLF4 signaling axis. Loss of SPRED2 enhanced proliferation, invasion, and chemoresistance in HCC cells, highlighting its tumor-suppressive role.To further elucidate the broader role of SPRED2 in tumor biology, we shifted our focus from intracellular signaling in HCC to intercellular communication within the tumor microenvironment. Using esophageal squamous cell carcinoma (ESCC) as a model, we demonstrated that SPRED2 suppresses exosome secretion by modulating multivesicular body (MVB)-associated proteins VAMP2 and Syntaxin 4 (STX4). Exosomes, nanosized vesicles released upon MVB-plasma membrane fusion, are critical mediators of intercellular signaling in cancer. Loss of SPRED2 markedly increased exosome release, suggesting that SPRED2 negatively regulates exosome biogenesis and secretion. Functionally, ESCC-derived exosomes were found to carry biologically active interleukin-6 (IL-6), which promotes tumor proliferation and metastasis through two major mechanisms: activation of STAT3 signaling in ESCC cells and induction of tumor-associated macrophage (TAM) polarization within the tumor microenvironment. Notably, exosomes derived from SPRED2-deficient ESCC cells enhanced both tumor cell aggressiveness and TAM polarization, whereas exosomes from SPRED2-overexpressing cells exhibited inhibitory effects on M1 and M2 macrophage polarization. The polarized macrophages, in turn, promoted ESCC proliferation and invasion via STAT3 activation, establishing a reciprocal feed-forward loop between tumor cells and immune cells. Furthermore, exosomes from polarized THP-1 cells significantly accelerated tumor progression in vivo, an effect that was effectively attenuated by Tocilizumab, an IL-6 receptor inhibitor.Collectively, our findings identify SPRED2 as a key regulator of exosome biogenesis and secretion through its interaction with VAMP2 and STX4. By controlling IL-6-enriched exosome release, SPRED2 modulates tumor-immune cell communication and suppresses the formation of a pro-tumorigenic microenvironment, extending its role from an intracellular suppressor of cancer stemness to a central coordinator of tumor-immune interactions. Citation Format: Tong Gao, Akihiro Matsukawa. Exosomes, regulated by SPRED2, reshape tumor microenvironment via activating IL6/ STAT3 signaling abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 7927.
Gao et al. (Fri,) studied this question.