Journal of Hepatology
Volume 41, Issue 5 , Pages 859-861, November 2004

Sustained activation of epidermal growth factor receptor in cholangiocarcinoma: a potent therapeutic target?

Department of Internal Medicine II, Faculty of Medicine, University of Miyazaki, 5200 Kihara, Kiyotake, Miyazaki 889-1601, Japan

published online 13 September 2004.

See Article, pages 808–814

Article Outline

 

Cholangiocarcinoma is a malignant neoplasm originating from epithelium of the biliary tree and is associated with a high rate of mortality [1]. It is the second most common primary malignant tumor of the liver after hepatocellular carcinoma, and comprises approximately 10% of all hepatobiliary malignancies. Specific mechanisms underlying the cellular and molecular pathogenesis of cholangiocarcinoma remain unclear. However, evidence suggesting that alterations in critical growth factor pathways may contribute to the development of this highly lethal cancer is accumulating.

Extrahepatic cholangiocarcinoma, which arises from large bile ducts, is more frequent than intrahepatic cholangiocarcinoma arising from small bile ducts. Both the large and small bile ducts, however, are lined with cholangiocytes [2]. Recently, large cholangiocytes arising from large bile ducts, but not small cholangiocytes from smaller bile ducts, have been shown to transport bile acids [3], and the heterogeneity of cholangiocytes along the biliary tract is now a well-established entity [4]. Therefore, in contrast to small bile duct cholangiocytes, specific characteristics of large bile duct cholangiocytes likely predispose to the development of this cancer.

One known risk factor for ductal cholangiocarcinoma is chronic inflammation, including primary sclerosing cholangitis (PSC), Clonorchis sinensis and opisthorchis viverrini infections (liver flukes), Caroli's disease, congenital choledochal cysts, and chronic intrahepatic lithiasis [5]. Also, in Japan, hepatitis C infection is frequently found in patients with intrahepatic cholangiocarcinoma [6]. Chronic inflammation is associated with cytokine generation from both inflammatory cells and cholangiocytes. A key proinflammatory cytokine is interleukin 6 (IL-6). A marked increase in serum levels of IL-6 has been observed in patients with cholangiocarcinoma. Moreover, IL-6 stimulates growth of cholangiocarcinoma cells by a mitogen-activated protein kinase (MAPK) signaling pathway, suggesting that IL-6 is a potent mitogen for cholangiocytes and cholangiocarcinoma cells [7], [8].

Ductal cholangiocarcinomas often grow within and along the bile duct lumen. These tumor cells can, therefore, survive and proliferate even in the toxic environment of bile. Alpini et al. have demonstrated that bile acids stimulate the proliferation of cholangiocytes and cholangiocarcinoma cells through a phosphatidylinositol 3-kinase (PI-3K)-dependent pathway [9], [10], [11]. PI-3K is stimulated by a number of mitogenic receptor tyrosine kinases. Recently, several investigations have reported that bile acids functionally transactivate the epidermal growth factor receptor (EGFR) in primary cultured hepatocytes or cholangiocarcinoma cells [12], [13]. Also, bile acids increase cellular protein levels of myeloid cell leukemia protein-1, a potent anti-apoptotic protein of the Bcl-2 family, via EGFR activation [14]. Therefore, transactivation of EGFR is thought to be an important mechanism by which bile acids stimulate cholangiocyte proliferation. The mechanism underlying bile acid-mediated EGFR transactivation is potentially both ligand-dependent and -independent [12], [14]. EGFR is usually activated by several ligands including EGF, transforming growth factor (TGF)-α, and heparin-binding EGF-like growth factor. Werneburg et al. have recently reported that bile acids activate EGF receptor via a TGF-α-dependent mechanism in a human cholangiocyte cell line [15]. Additionally, since matrix metalloproteinase (MMP) activity is required for TGF-α release from cellular membranes and ligand function, bile acid-induced EGFR activation and cell growth are inhibited by an MMP inhibitor. Conversely, ligand-independent signaling of EGFR occurs by processes, usually overexpression, which promote receptor oligomerization in the plasma membrane [16]. Indeed, overexpression and aberrant function of EGFR have been observed in several human carcinomas, and hence, the EGFR-tyrosine kinase is a selective therapeutic target for inhibiting tumor growth. Although EGFR signaling plays an important role in the pathogenesis and progression of cholangiocarcinoma, the characteristics of EGFR signaling in cholangiocarcinoma cells have not been fully understood.

Yoon and co-workers report details of the mechanism for overexpression of EGFR and its sustained activation in human cholangiocarcinoma cells in this issue of the Journal [17]. They found that, when cholangiocarcinoma cells were treated with EGF, EGFR activation was sustained resulting in extended MAPK activation and growth stimulation. Also, they demonstrated that, even though EGFR is promptly ubiquitinated following ligand-induced activation, its internalization is either defective or delayed in cholangiocarcinoma cells, leading to prolonged expression of EGFR on the plasma membrane after exposure to EGF, thereby sustaining its activation. A ubiquitin ligase, c-Cbl, is activated by EGFR, and c-Cbl-mediated ubiquitination of active EGFR is essential for receptor degradation [18]. Also, formation of the endocytotic complex at the plasma membrane, comprised of c-Cbl, CIN85 (Cbl-interacting protein of 85K) and endophilins, is critical for receptor internalization [19], [20]. Inhibition of these interactions has recently been shown to block EGFR internalization, delay receptor degradation, and enhance EGFR signaling transduction, without perturbing c-Cbl-direct receptor ubiquitination [21]. Thus, the findings in this issue indicate the possibility that human cholangiocarcinoma cells lack interaction between c-Cbl and CIN85/endophilin.

Cyclooxygenase (COX)-2, a crucial rate-limiting enzyme in prostaglandin metabolism, has been shown to inhibit apoptosis, promote angiogenesis, and facilitate cellular growth in a variety of malignancies [22]. This enzyme can be induced by various proinflammatory cytokines in biliary epithelial cells, and has been implicated in cholangiocarcinogenesis [23]. Recently, bile acid transactivation of EGFR has been reported to induce COX-2 expression through a MAPK cascade [13]. In this issue, Yoon et al. also demonstrate that EGFR kinase inhibitors decreased COX-2 expression in human cholangiocarcinoma cells, and that cell growth was significantly inhibited by treatment with EGFR kinase inhibitors as well as a COX-2 inhibitor [17]. Therefore, either EGFR or COX-2 are promising drug targets for cholangiocarcinoma, and their inhibition has the potential to treat and prevent this cancer. However, expression of c-Met, a specific receptor for hepatocyte growth factor (HGF), is also observed in a significant percentage of human cholangiocarcinomas by immunohistochemistry [24], and the growth of human cholangiocarcinoma cells have been shown to be stimulated by HGF as well as IL-6 [25]. Additionally, treatment with HGF or IL-6 induced the rapid phosphorylation of cytosolic phopholipase A2 (cPLA2), another crucial rate-limiting enzyme in prostaglandin metabolism, and HGF- and IL-6-induced proliferation of cholangiocarcinoma cells was significantly inhibited by either a cPLA2 or COX-2 inhibitor [25]. Therefore, although clinical studies of anti-EGFR therapeutic strategies, including the EGFR tyrosine kinase inhibitor ZD1839 (Iressa; AstraZeneca Pharmaceuticals LP, Wilmington, DE), have shown clinical responses in a variety of solid tumors [16], it is necessary to carefully evaluate whether therapeutic targeting of only EGFR can induce sufficient effect on established cholangiocarcinoma. Conversely, a selective COX-2 inhibitor, celecoxib, being developed as a potential treatment for rheumatoid arthritis and osteoarthritis, can be used as a potent chemopreventive agent in different types of cancer [26]. The role of selective COX-2 inhibitors as chemopreventive agents for cholangiocarcinoma needs to be assessed in patients with PSC, which is one risk factor for cholangiocarcinoma [1]. Also, the mechanisms and the molecular pathology of the chemopreventive effects should be further clarified. However, extensive investigations to understand alterations in tyrosine kinase receptor signaling including EGFR and the role of COX-2 expression in cholangiocarcinoma cells or cholangiocarcinogenesis would provide a potent therapeutic or chemopreventive modality for cholangiocarcinoma, a nefarious neoplasm of the bile duct apparatus.

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References 

  1. Gores GJ. Cholangiocarcinoma: current concepts and insights. Hepatology. 2003;37:961–969
  2. Nakeeb A, Pitt HA, Sohn TA, Coleman J, Abrams RA, Piantadosi S, et al. Cholangiocarcinoma. A spectrum of intrahepatic, perihilar, and distal tumors. Ann Surg. 1996;224:463–473
  3. Alpini G, Glaser SS, Rodgers R, Phinizy JL, Robertson WE, Lasater J, et al. Functional expression of the apical Na+-dependent bile acid transporter in large but not small rat cholangiocytes. Gastroenterology. 1997;113:1734–1740
  4. Kanno N, LeSage G, Glaser S, Alvaro D, Alpini G. Functional heterogeneity of the intrahepatic biliary epithelium. Hepatology. 2000;31:555–561
  5. Kahn SA, Davidson BR, Goldin R, Pereira SP, Rosenberg WM, Taylor-Robinson SD, et al. Guidelines for the diagnosis and treatment of cholangiocarcinoma: consensus document. Gut. 2002;51:V11–V19
  6. Okuda K, Nakamura Y, Miyazaki M. Cholangiocarcinoma: recent progress. Part 1: epidemiology and etiology. J Gastroenterol Hepatol. 2002;17:1049–1055
  7. Goydos JS, Brumfield AM, Frezza E, Booth A, Lotze MT, Carty SE. Marked elevation of serum interleukin-6 in patients with cholangiocarcinoma: validation of utility as a clinical marker. Ann Surg. 1998;227:398–404
  8. Park J, Tadlock L, Gores GJ, Patel T. Inhibition of interleukin 6-mediated mitogen-activated protein kinase activation attenuates growth of a cholangiocarcinoma cell line. Hepatology. 1999;30:1128–1133
  9. Alpini G, Glaser S, Robertson W, Phinizy JL, Rodgers RE, Caligiuri A, et al. Bile acids stimulate proliferative and secretary events in large but not small cholangiocytes. Am J Physiol Gastrointest Liver Physiol. 1997;273:G518–G529
  10. Alpini G, Glaser S, Ueno Y, Rodgers R, Phinizy JL, Francis H, et al. Bile acid feeding induces cholangiocyte proliferation and secretion: evidence for bile acid-regulated ductal secretion. Gastroenterology. 1999;116:179–186
  11. Alpini G, Glaser S, Alvaro D, Ueno Y, Marzioni M, Francis H, et al. Bile acid depletion and repletion regulate cholangiocyte growth and secretion by a phosphatidylinositol 3-kinase-dependent pathway in rats. Gastroenterology. 2002;123:1226–1237
  12. Qiao L, Studer E, Leach K, McKinstry R, Gupta S, Decker R, et al. Deoxycholic acid (DCA) causes ligand-independent activation of epidermal growth factor receptor (EGFR) and FAS receptor in primary hepatocytes: inhibition of EGFR/mitogen-activated protein kinase-signaling module enhances DCA-induced apoptosis. Mol Biol Cell. 2001;12:2629–2645
  13. Yoon JH, Higuchi H, Werneburg NW, Kaufmann SH, Gores GJ. Bile acids induce cyclooxygenase-2 expression via the epidermal growth factor receptor in a human cholangiocarcinoma cell line. Gastroenterology. 2001;122:985–993
  14. Yoon JH, Werneburg NW, Higuchi H, Canbay AE, Kaufmann SH, et al. Bile acids inhibit Mcl-1 protein turnover via an epidermal growth factor receptor/Raf-1-dependent mechanism. Cancer Res. 2002;62:6500–6505
  15. Werneburg NW, Yoon JH, Higuchi H, Gores G. Bile acids activate EGF receptor via a TGF-a-dependent mechanism in human cholangiocyte cell line. Am J Physiol Gastrointest Liver Physiol. 2003;285:G31–G36
  16. Ritter CA, Arteaga CL. The epidermal growth factor receptor-tyrosine kinase: a promising therapeutic target in solid tumors. Semin Oncol. 2003;30:3–11
  17. Yoon J-H, Gwak G-Y, Lee H-S, Bronk SF, Werneburg NW, Gores GJ. Enhanced epidermal growth factor receptor activation in human cholangiocarcinoma cells. J Hepatol. 2004;41:808–814
  18. de Melker AA, van der Horst G, Calafat J, Jansen H, Borst J. c-Cbl ubiquitinates the EGF receptor at the plasma membrane and remains receptor associated throughout the endocytic route. J Cell Sci. 2001;114:1267–2178
  19. Schmidt A, Wolde M, Thiele C, Fest W, Kratzin H, Podtelejnikov AV, et al. Endophilin I mediates synaptic vesicle formation by transfer of arachidonate to lysophosphatidic acid. Nature. 1999;401:133–141
  20. Take H, Watanabe S, Takeda K, Yu ZX, Iwata N, Kajigaya S. Cloning and characterization of a novel adaptor protein, CIN85, that interacts with c-Cbl. Biochem Biophys Res Commun. 2000;268:321–328
  21. Soubeyran P, Kowanetz K, Szymkiewicz I, Langton WY, Dikic I. Cbl-CIN85-endophilin complex mediates ligand-induced downregulation of EGF receptors. Nature. 2002;416:183–187
  22. Gupta RA, Dubois RN. Colorectal cancer prevention and treatment by inhibition of cyclooxygenase-2. Nat Rev Cancer. 2001;1:11–21
  23. Nzeako UC, Guicciardi ME, Yoon JH, Bronk SF, Gores GJ. COX-2 inhibits Fas-mediated apoptosis in cholangiocarcinoma cells. Hepatology. 2002;35:552–559
  24. Terada T, Nakanuma Y, Sirica AE. Immunohistochemical demonstration of MET overexpression in human intrahepatic cholangiocarcinoma and in hepatolithiasis. Hum Pathol. 1998;29:175–180
  25. Wu T, Han C, Lunz JG, Michalopoulos G, Shelhamer JH, Demetris AJ. Involvement of 85-kd cytosolic phospholipase A2 and cyclooxygenase-2 in the proliferation of human cholangiocarcinoma cells. Hepatology. 2002;36:363–373
  26. Kismet K, Akay T, Abbasoglu O, Ercan A. Celecoxib: a potent cyclooxygenase-2 inhibitor in cancer prevention. Cancer Detect Prev. 2004;28:127–142

PII: S0168-8278(04)00396-4

doi:10.1016/j.jhep.2004.09.003

Journal of Hepatology
Volume 41, Issue 5 , Pages 859-861, November 2004

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