SIRT1 induces the accumulation of TAMs at colorectal cancer tumor sites via the CXCR4/CXCL12 axis.

Our previous work suggested that high SIRT1 expression by cancer cells predicted a poor colorectal cancer (CRC) prognosis, but its role in the tumor microenvironment was unclear. Here, we examined tumor-infiltrating lymphocytes (TILs) in CRC expressing different levels of SIRT1. We also established a co-culture system with monocytes, CD8 T cells and patient-derived tumor organoids (PDOs) to study the relationships between immune cells and cancer cells. The percentage of CD8 T cells was decreased and the percentage of macrophages was increased in SIRT1-high (SIRT1-hi) CRC. Co-culture results showed that tumor-associated macrophages (TAMs) from SIRT1-hi CRC inhibited the proliferation and anti-tumor activity of CD8 T cells. Importantly, SIRT1-hi CRC were shown to modulate the migration and the activity of TAMs. RNA sequencing revealed that CD14 monocytes in SIRT1-hi patients expressed higher levels of CXCR4. Mechanistically, SIRT1 expression was shown to promote CXCL12 expression by inhibiting the acetylation of p53. Our findings indicate that SIRT1 in CRC induces TAM migration through the CXCR4/CXCL12 pathway, and inhibits the proliferation and activity of CD8 T cells, resulting in promotion of CRC progression.