An Unconventional KITENIN/ErbB4-Mediated Downstream Signal of EGF Upregulates c-Jun and the Invasiveness of Colorectal Cancer Cells

Abstract

Purpose: EGF-stimulated signaling via EGF receptor (EGFR) is important in colorectal tumorigenesis and drug targeting. However, anti-EGFR therapy is not effective in a subset of patients with colorectal cancer, suggesting that unidentified EGF-stimulated pathways might play roles in colorectal cancer. Previously, we identified KAI1 C-terminal interacting tetraspanin (KITENIN) as a metastasis-enhancing gene and found it to be highly expressed in sporadic colorectal cancer tissues. We recently found that EGF further increases KITENIN-induced elevated AP-1 activity. Here we attempted to clarify this novel EGF-stimulated molecular pathway and its roles in colorectal cancer.Experimental Design: We analyzed how EGF modulates the downstream signaling pathway of oncogenic KITENIN in colorectal cancer cells. Biological alterations following EGF treatment were identified in KITENIN-overexpressed colorectal cancer cells with or without alteration of EGFR activity.Results: We identified the KITENIN/ErbB4-Dvl2-c-Jun axis as a novel downstream signal of EGF that is switched on under elevated KITENIN conditions in an EGFR-independent manner. This unconventional EGF signal upregulates c-Jun and enhances invasion and anchorage-independent growth of colorectal cancer cells. In addition, tumor tissues from metastatic patients with colorectal cancer who showed initial poor responses to cetuximab/chemotherapy expressed higher levels of KITENIN than did responders to therapy.Conclusions: Our results highlight the role of an EGFR-independent EGF signal in mediating the invasiveness and tumorigenesis of colorectal cancer cells. This unconventional pathway might be related to the limited clinical efficacy of anti-EGFR agents in a subset of patients with colorectal cancer. Clin Cancer Res; 20(15); 4115-28. Ó2014 AACR.

Elevated Coexpression of KITENIN and the ErbB4 CYT-2 Isoform Promotes the Transition from Colon Adenoma to Carcinoma Following APC loss

“…EGFR signaling was previously reported to upregulate its cognate ligands in nontransformed rat intestinal epithelial cells and thereby create autocrine loops that maintain and amplify levels of EGFR activity (28). In addition, it was previously reported that levels of EGF/ EGFR are significantly increased in tumor samples compared with the surrounding mucosa in patients with colorectal cancer (34), and our previous results showed that elevated KITENIN in colorectal cancer cells can act as an oncogenic molecular switch that transduces and amplifies AP-1-activating signals from extracellular growth factors, such as EGF (14,21). In this study, we found that elevated KITENIN promotes the transition of colon adenoma to early-stage adenocarcinoma within an APC loss-associated tumor microenvironment, consisting of predominant overexpression of ErbB4-CYT-2 and increased EGFR expression.…”

“…4A, right). Actually, upregulated cell invasion was also observed following EGF treatment in ErbB4 JM-a/CYT-2-transfected HCT116 cells, compared with empty vector-transfected HCT116 cells (21). Therefore, these in vitro data propose that the oncogenic activity of elevated KITENIN can be manifested under preferential overexpression of ErbB4-CYT-2.…”

“…Previously, we reported on the effects of elevated KITENIN on cell migration and invasion (14,21). We selected untransformed RIE cells for overexpression and transformed Caco2 cells for knockdown.…”

“…Furthermore, elevated KITENIN expression accompanies the phenotype of early stage invading adenocarcinoma in KIT-TG/APC min/þ mice. In human colorectal cancer tissues, expression of ErbB4-CYT-2 is elevated in tissues in which a higher level of endogenous KITENIN is expressed (14,21) and a positive correlation was found between KITENIN and ErbB4-CYT-2 expression in pooled adenoma and adenocarcinoma tissues. These finding reiterate the importance of elevated expression of KITENIN and ErbB4-CYT-2 in the malignant progression of adenoma.…”

“…We also found a higher level of endogenous KITENIN in colorectal cancer tissues from advanced stages of colorectal cancer and elucidated that the interaction of KITENIN with Dvl is important in regulating colorectal cancer cell invasion (14). We recently identified the KITENIN/ErbB4-c-Jun axis as a novel downstream signal of EGF that is switched on under elevated KITENIN in an EGFR-independent manner and that upregulates c-Jun and enhances the invasion and anchorage-independent growth of colorectal cancer cells (21). Until now, however, studies in an in vivo mouse model to demonstrate whether elevated expression of KITENIN/ErbB4 drives the progression of colorectal cancer in the tumor-associated microenvironment have not been undertaken.…”