<i>Fusobacterium nucleatum</i> Promotes Metastasis in Colorectal Cancer by Activating Autophagy Signaling via the Upregulation of CARD3 Expression

Abstract

<b>Aims</b>: We aimed to measure the abundance of <i>Fusobacterium nucleatum</i> (<i>F. nucleatum</i>) in colorectal cancer (CRC) tissues from patients and to uncover the function of this bacterium in colorectal tumor metastasis. <b>Methods</b>: We collected metastatic and non-metastatic CRC tissues to analyze <i>F. nucleatum</i> abundance. Cells were incubated with <i>F. nucleatum</i> or chloroquine (CQ) or were transfected with CARD3-targeting siRNA; the expression of mRNAs and proteins was then measured. CRC cells stably transfected with shRNA-luc were mixed with <i>F. nucleatum</i> and intravenously injected into BALB/cJ mice. APC^Min/+, CARD3^-/-and CARD3^wt C57BL mice were given <i>F. nucleatum</i>; some mice were given azoxymethane (AOM) and dextran sodium sulfate (DSS). <b>Results</b>: <i>F. nucleatum</i> was abundant in CRC tissues from patients with metastasis. <i>F. nucleatum</i> infection increased CRC cell motility and upregulated the expression of CARD3, LC3-II, Beclin1 and Vimentin, and downregulated the expression of E-cadherin and P62 in CRC cells. These effects were attenuated by treatment with CQ, siCARD3 or both. APC^Min/+ mice gavaged with <i>F. nucleatum</i> developed more aggressive tumors than control mice. After AOM/DSS administration, the colorectums of CARD3^-/- mice had fewer tumors than those of control mice. Tumors from CARD3^-/- mice had lower levels of LC3-II and Beclin1 and higher levels of P62 than those from control mice. BALB/cJ mice injected with both CT26-luc cells and <i>F. nucleatum</i> formed more metastases than control mice. CQ treatment, CARD3 knockdown or both reduced the ability of CT26-luc cells to form metastases <i>in vivo</i>. <b>Conclusions</b>: <i>F. nucleatum</i> is enriched in CRC tissues from patients with metastasis. <i>F. nucleatum</i> orchestrates CARD3 and autophagy to control CRC metastasis. Measuring and targeting <i>F. nucleatum</i> and its associated pathways will yield approaches for the prevention and treatment of CRC metastasis.