Heregulin-induced VEGF expression via the ErbB3 signaling pathway in colon cancer.
OBJECTIVE
Heregulin (HRG/NRG) ligation to erbB3/4 promotes their respective heterodimerization with erbB2, and consequent erbB2 tyrosine phosphorylation. Although HRG has been shown to be expressed in a variety of cancer tissues, its expression and role in colon cancer have yet to be clarified. We therefore examined the link between the expression of these erbB receptors, and the relationship between HRG and vascular endothelial growth factor (VEGF) expression in colon cancer.


METHODS
We analyzed the effects of HRG on VEGF secretion in 6 colorectal cancer cell lines by enzyme-linked immunosorbent assay, and HRG-induced p85 subunit of phosphatidylinositol 3-kinase (p85 PI-3K), Akt, extracellular signal-regulated kinase 1/2 (ERK1/2), and p38 mitogen-activated protein kinase (p38 MAPK) activation in Caco-2 colon cancer cell lines by Western blot. We also examined HRG and VEGF mRNA expression in 16 colon cancer biopsy samples by real-time PCR. The localization of HRG and VEGF protein expression in colon cancer tissue was detected by immunohistochemistry.


RESULTS
Exogenous HRG stimulated VEGF secretion in all cell lines examined, and VEGF mRNA expression in Caco-2 cells. HRG also activated p85 PI-3K, Akt, ERK1/2, and p38 MAPK. VEGF secretion was inhibited by both specific p38 MAPK inhibitor and proteasome inhibitor that inhibit nuclear factor kappa B (NF-kappaB) activation. In colon cancer biopsy samples, HRG mRNA expression correlated with VEGF mRNA expression. HRG immunoreactivity was observed both in cancer cells and in mesenchymal cells in colon cancer tissues.


CONCLUSIONS
These data suggest that HRG might affect colon cancer growth by regulating VEGF secretion via the erbB3 signaling pathway through autocrine and paracrine mechanisms.
Yonezawa
Masaoki
M
Division of Gastroenterology, Nippon Medical School, Tokyo, Japan.
Wada
Ken
K
Tatsuguchi
Atsushi
A
Akamatsu
Tomonori
T
Gudis
Katya
K
Seo
Tsuguhiko
T
Mitsui
Keigo
K
Nagata
Kazuhiro
K
Tanaka
Shu
S
Fujimori
Shunji
S
Sakamoto
Choitsu
C
D000230:Adenocarcinoma / Q000378:metabolism*; D018938:Caco-2 Cells; D003110:Colonic Neoplasms / Q000378:metabolism*; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D019073:HT29 Cells; D006801:Humans; D007150:Immunohistochemistry; D007413:Intestinal Mucosa / Q000378:metabolism; D020935:MAP Kinase Signaling System; D020890:Neuregulin-1 / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation; D016133:Polymerase Chain Reaction; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D020893:Receptor, ErbB-3 / Q000378:metabolism*; D042461:Vascular Endothelial Growth Factor A / Q000378:metabolism*
D020890:Neuregulin-1; D012333:RNA, Messenger; D042461:Vascular Endothelial Growth Factor A; D019869:Phosphatidylinositol 3-Kinases; D020893:Receptor, ErbB-3; D051057:Proto-Oncogene Proteins c-akt; D048049:Extracellular Signal-Regulated MAP Kinases