Hyaluronic acid (HA), a constituent of the extracellular matrix, promotes
colorectal cancer growth. CD44 is a relevant HA receptor in this context. However, HA is also a
ligand for TLR4, a receptor of significance in
colorectal cancer. In this study, we examine the relative contribution of HA interactions with CD44 and TLR4 in colon
tumorigenesis.
Colorectal cancer models included ApcMin/+ mice,
azoxymethane/
dextran sodium sulfate (AOM-DSS), and CT26
tumor isografts. We used knockout mice and CT26
colorectal cancer cells with CRISPR knockdown of CD44 and TLR4. HA activity was modulated by PEP1 (a 12-mer
peptide that blocks HA from binding its receptors),
hyaluronidase (which promotes HA degradation), or 4-MU (HA synthesis inhibitor). Blockade of HA binding via PEP1 decreased growth in all
colorectal cancer models and in cell culture. The effects were significant in WT and with CD44 deletion, but not with TLR4 deletion. In the AOM-DSS model, mice deficient in CD44 or TLR4 had fewer
tumors. CD44- and TLR4-deficient CT26 isografts grew more slowly, exhibiting decreased
tumor cell proliferation and increased apoptosis. In vitro, endogenous HA blocked LPS binding to TLR4 suggesting that HA is a relevant TLR4
ligand in
colon cancer. Finally, PEP1 enhanced
tumor radiation sensitivity in the isograft model. Together, these results indicate that HA binding to TLR4, as well as CD44, plays a key role in colon
tumorigenesis. These findings also raise the possibility that an agent that blocks HA binding, such as PEP1, may be useful as an adjuvant
therapy in
colon cancer.