Abstract
Colorectal cancer (CRC) is prevalent worldwide. Dietary consumption of procyanidins has been linked to a reduced risk of developing CRC. The epidermal growth factor (EGF) receptor (EGFR) signaling pathway is frequently dysregulated in CRC. Our earlier research showed that the procyanidin dimers of epicatechin gallate (ECG) and epigallocatechin gallate (EGCG), through their interaction with lipid rafts, inhibit the EGFR signaling pathway and decrease CRC cell growth. The process of cancer cell invasion and metastasis involves matrix metalloproteinases (MMPs), which are partially EGFR-regulated. This study investigated whether ECG and EGCG dimers can inhibit EGF-induced CRC cell invasion by suppressing the redox-regulated activation of the EGFR/MMPs pathway. Both dimers mitigated EGF-induced cell invasion and the associated increase of MMP-2/9 expression and activity in different CRC cell lines. In Caco-2 cells, both dimers inhibited the activation of the EGFR and downstream of NF-κB, ERK1/2 and Akt, which was associated with decreased MMP-2/9 transcription. EGF induced a rapid NOX1-dependent oxidant increase, which was diminished by both ECG and EGCG dimers and NOX inhibitors (apocynin, Vas-2870, DPI). Both dimers inhibited NOX1 gene expression, as well as NOX1 activity with evidence of direct binding to NOX1. Both dimers, all NOX chemical inhibitors and NOX1 silencing inhibited EGF-mediated activation of the EGFR signaling pathway and the increased MMP-2/9 mRNA levels and activity. Pointing to the relevance of NOX1 on ECG and EGCG dimer effects on CRC invasiveness, silencing of NOX1 also inhibited EGF-stimulated Caco-2 cell invasion. In summary, ECG and EGCG dimers can act inhibiting CRC cell invasion/metastasis both, by downregulating MMP-2 and MMP-9 expression via a NOX1/EGFR-dependent mechanism, and through a direct inhibitory effect on MMPs enzyme activity.