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.