Semaphorin-3F suppresses the stemness of colorectal cancer cells by inactivating Rac1

• Low level of SEMA3F in CRC is associated with poor prognosis of patients.
• SEMA3F inhibits the capability of cell self-renewal and clone formation of cancer cells in vitro and tumorigenesis in vivo.
• Rac1 activation plays a crucial role in stemness inhibited by SEMA3F.
• Combination of SEMA3F and GTP-Rac1 is an independent prognosticator of overall survival of patients.

Tumor cell stemness has been recognized as a key contributor to tumor initiation, progression and recurrence. Our previous studies have found that semaphorin-3F (SEMA3F), an axon guidance molecule in the development of central nervous system, inhibited the growth and metastasis of colorectal cancer (CRC). However, a possible role for SEMA3F in regulating cancer cell stemness remains unknown. Here, we report a novel mechanism of the acquirement of stemness of CRC cells regulated by SEMA3F. Knockdown of SEMA3F significantly promoted the self-renewal and tumorigenicity of CRC cells, and increased the expression of stemness-associated genes, while overexpressing SEMA3F reduced the stemness of CRC cells. Mechanistically, GTP-Rac1 was involved in SEMA3F mediated regulation of CRC cell stemness by targeting the Wnt/β-catenin pathway. Clinically, GTP-Rac1 expression was inversely correlated with SEMA3F levels in CRC samples and patients with SEMA3Flow/GTP-Rac1high CRC showed poorer prognosis. Our findings demonstrate the ability of SEMA3F to inhibit the stemness of human CRC cells by suppressing Rac1 activation, which suggests a novel therapeutic approach for CRC.