L1, a neuronal cell adhesion receptor of the
immunoglobulin-like
protein family is expressed in invading
colorectal cancer (CRC) cells as a target gene of Wnt/β-
catenin signaling. Overexpression of L1 in CRC cells enhances cell motility and proliferation, and confers liver
metastasis. We recently identified
ezrin and the IκB-NF-κB pathway as essential for the
biological properties conferred by L1 in CRC cells. Here, we studied the underlying molecular mechanisms and found that L1 enhances
ezrin phosphorylation, via Rho-associated
protein kinase (ROCK), and is required for L1-ezrin co-localization at the juxtamembrane domain and for enhancing cell motility. Global transcriptomes from L1-expressing CRC cells were compared with transcriptomes from the same cells expressing
small hairpin RNA (
shRNA) to
ezrin. Among the genes whose expression was elevated by L1 and
ezrin we identified
insulin-like growth factor-binding protein 2 (IGFBP-2) and showed that its increased expression is mediated by an NF-κB-mediated transactivation of the
IGFBP-2 gene promoter. Expression of a constitutively activated mutant
ezrin (Ezrin567D) could also increase
IGFBP-2 levels in CRC cells. Overexpression of
IGFBP-2 in CRC cells lacking L1-enhanced cell proliferation (in the absence of serum), cell motility,
tumorigenesis and induced liver
metastasis, similar to L1 overexpression. Suppression of endogenous
IGFBP-2 in L1-transfected cells inhibited these properties conferred by L1. We detected
IGFBP-2 in a unique organization at the bottom of human colonic crypts in normal mucosa and at increased levels throughout human CRC tissue samples co-localizing with the phosphorylated p65 subunit of NF-κB. Finally, we found that
IGFBP-2 and L1 can form a molecular complex suggesting that L1-mediated signaling by the L1-ezrin-NF-κB pathway, that induces
IGFBP-2 expression, has an important role in CRC progression.