Tumor-derived C4BPA promotes macrophage M2-like polarization through C5a -C5aR1-STAT3 axis and drives gastric cancer progression

Background: C4b-binding protein α (C4BPA) is a soluble complement regulator reported to be altered in several malignancies, but its role in gastric Cancer (GC) biology and tumor-immune crosstalk remains unclear.

Methods: We generated C4BPA knockdown and overexpression GC cell lines, assessing proliferation, migration, and invasion in vitro. Furthermore, patient-derived GC organoids were engineered to overexpress C4BPA to assess its impact on Organoid growth and size. In vivo tumor growth was evaluated in a subcutaneous mouse xenograft model. Mechanistic studies measured Janus kinase 2/ Signal transducer and activator of transcription 3 (JAK2/STAT3) phosphorylation and complement expression in tumor cells. We performed co-culture experiments with THP-1-derived macrophages to assess macrophage STAT3 activation and M2 marker expression.

Results: C4BPA knockdown markedly suppressed GC cell proliferation and reduced migration and invasion in vitro, whereas C4BPA overexpression produced the opposite effects. Consistently, C4BPA overexpression in patient-derived GC organoids resulted in faster growth and larger Organoid size. Tumors formed by C4BPA-depleted cells grew substantially slower in mice. Mechanistically, C4BPA loss reduced phosphorylation of JAK2 and STAT3 in tumor cells and decreased production of C3a and C5a. Co-culture of C4BPA-deficient tumor cells with macrophages led to attenuated macrophage STAT3 signaling and downregulation of M2 polarization markers. Recombinant human C5a dose-dependently increased macrophage p-STAT3 through C5a receptor 1 (C5aR1) and restored M2 marker expression in the shC4BPA co-culture condition.

Conclusions: C4BPA promotes gastric tumor cell proliferation and motility and shapes a pro-tumoral M2 macrophage phenotype. These data nominate the C4BPA → C5a → C5aR1 → STAT3 axis as a candidate immunomodulatory pathway in GC and suggest C4BPA as a potential therapeutic target.

C4BPA; C5aR1-STAT3; Gastric cancer; JAK–STAT; Macrophage polarization.