HN1/CEBPB/CCL2 signaling shapes VSIG4⁺ tumor-associated macrophages in anaplastic thyroid carcinoma

V-set and immunoglobulin domain-containing protein 4 (VSIG4) positive tumor-associated macrophage (VSIG4⁺ TAM) is an immunosuppressive subpopulation specifically infiltrates anaplastic thyroid carcinoma (ATC) tissues and drives tumor growth. However, the mechanisms by which ATC cells shape the VSIG4⁺ TAM immunophenotype remain unclear. We screen for the cytokine essential for inducing VSIG4⁺ TAMs using cytokine array screening and coculture validation. This reveals that CC motif chemokine ligand 2 (CCL2) is highly expressed in ATC cells and promotes VSIG4⁺ macrophage differentiation. Both CCL2-neutralizing antibody and CCL2 knockdown significantly inhibits macrophage migration and the proportion of VSIG4⁺ macrophages induced by ATC cells. Notably, the combination of CCL2 and VSIG4 blockade synergistically alleviates the growth of subcutaneously transplanted tumors in mice and reshaped the immunosuppressive microenvironment of ATC tumors. Further study showed that the expression of CCL2 is regulated by hematological and neurological expressed 1 (HN1) in ATC cells, and HN1-CCL2 signaling induces VSIG4⁺ macrophage differentiation via activation of the CCR2/PI3K/AKT pathway. HN1 forms complex with transcription factor CCAAT/enhancer binding protein beta (CEBPB) to prevent CEBPB from ubiquitination and degradation, thereby promoting CCL2 transcription. In summary, our findings demonstrate HN1/CCL2/VSIG4 axis is essential for fostering immunosuppressive microenvironment in ATC, shedding light on potential targets concerning cancer cell-TAMs crosstalk.