CHOLESTEATOMA GROWTH AND PROLIFERATION: EXPRESSION OF HGF (HEPATOCYTE GROWTH FACTOR) AND ITS HIGH-AFFINITY RECEPTOR C-MET
Introduction
Cholesteatoma is epidermally-derived temporal bone lesion that is locally destructive and frequently recurrent. There are no medical therapies for cholesteatoma and currently the only available treatment is surgical resection. Despite many studies, the molecular events governing cholesteatoma formation are not well established.1 It is clear that when squamous epithelium lining the external ear canal (EAC) or the tympanic membrane (TM) becomes trapped into the middle ear (ME)(retraction pockets), a process of hyper-proliferation ensues. Cholesteatoma is actually a hyper-proliferative disease in which keratinocytes (KC) at all levels of the epithelium show both increased proliferation rates and decreased rates of programmed cell death (apoptosis).2,3 The application of molecular biology to clinical investigation of cholesteatoma should bring us to a new understanding of this disease with implied benefits of new therapies.
Materials and methods
Total RNA (tRNA) was extracted from cholesteatoma and control EAC skin for each patient (n = 10). Then cDNAs derived from tRNA were hybridized with GeneChip Human Genome U133 Plus 2.0 Array for both tissues. The data were analyzed with GeneSpring GX, and both up-regulated (three times higher than the control) and down-regulated (1/3 lower than the control) genes expressed in cholesteatoma were determined.
Results
DNA microarray analyses indicated that both HGF and C-MET were up-regulated by five to ten times in all cholesteatomas (n = 10). Real-time PCR analysis confirmed that mRNAs of both HGF and C-MET were up-regulated by five to15 times in all cholesteatomas.
Immunohistochemical studies indicated that HGF was predominantly expressed in infiltrated monocytes and macrophages just beneath the cholesteatoma epithelium, while C-MET was expressed in the entire cho-lesteatoma epithelium (Fig. 1A,B).
Fig. 1. Expressions of HGF & C-MET in cholesteatoma tissue. A: C-MET expression in the epithelium (red arrows) and sub-epithelial layers (black arrow heads); B: HGF expressions in the cholesteatoma epithelium (red arrows) and sub-epithelial layers (black arrow heads); C: negative control.
Discussion
HGF was first identified as a potent mitogen for fully differentiated hapatocyte, and it is currently known to have multiple biological activities on a wide variety of cells via its binding to C-MET receptor.4 HGF has been shown to have critical roles in both KC proliferation and apoptosis. HGF may stimulate phosphatidylinositol 3-kinase (PI3K), leading activation of Akt. HGF may protect KC against apoptosis by maintaining of levels of Bcl-2 and Bcl-XL and by activating Akt. HGF could promote KCs proliferation and prevent KCs apoptosis, resulting in abnormal KCs growth.2 The present study suggests that HGF might induce KC proliferation in cholesteatoma epithelium through up-regulations of both HGF and C-MET in autocrine as well as paracrine manner (Fig. 2A).
The discovery of NK4 as an HGF-antagonist has promoted research in cancer biology, pathology and therapy. Growing evidence indicates that NK4 inhibits tumor growth, invasion and metastasis in animal models of various types of malignant tumors. Several approaches to inhibit HGF-C-MET signaling are now being developed as an anti-cancer agent. In future, the relatively easy access of the ME to intra-tympanic drug delivery makes HGF/C-MET-related RNA/DNA-based topical inhibitors of cholesteatoma an attractive mode of primary or adjunctive medical therapy (Fig. 2B).
Fig. 2. Keratinocytes hyperproliferation and HGF. A: Autocrine and paracrine actions of HGF; B: Development of a HGF/C-MET-related new medical therapy.
References
1.Albino AP, Kimmelman CP et al. Cholesteatoma: a molecular and cellular puzzle. Am J Otol 19:7–19, 1998
2.Raj D, Brash DE, et al. J Invest Dermatol 126: 243–257, 2006
3.Hamajima Y, Komori M et al. The role of inhibitor of DNA-binding (ld1) in hyperproliferation of keratinocytes: the pathological basis for middle ear cholesteatoma derived from chronic otitis media. Cell Prolif 43:457–463, 2010
4.Nakamura T, Mizuno S. The discovery of hepatocyte growth factor (HGF) and its significance for cell biology, life science and clinical medicine. Proc Jpn Acad Ser B 86:588–610, 2010
Address for correspondence: Katsumi Doi, MD/PhD, 377–2, Oono-Higashi, Osaka-Sayama, 589–8511, Osaka, Japan. kdoi@med.kindai.ac.jp
Cholesteatoma and Ear Surgery – An Update, pp. 29–31
Edited by Haruo Takahashi
2013 © Kugler Publications, Amsterdam, The Netherlands