Growth inhibition by keratinocyte growth factor receptor of human salivary adenocarcinoma cells through induction of differentiation and apoptosis

Abstract

We have reported that normal human salivary gland-derived epithelial cells exclusively express keratinocyte growth factor receptor (KGFR). In the process of malignant transformation of human salivary gland tumors, KGFR gene expression disappeared concomitantly with the de novo expression of the fibroblast growth factor receptor 1 (FGFR1) and FGFR4 genes. In the present study, we introduced wild-type KGFR cDNA or chimeric KGFR͞ FGFR1 cDNA, which encoded the extracellular domain of KGFR and the intracellular domain of FGFR1, into the HSY human salivary adenocarcinoma cell line. The KGFR tyrosine kinase suppressed the activity of FGF receptor substrate 2 (FRS2) and inhibited the growth of HSY by inducing differentiation and apoptosis in vitro and in vivo. Our results provided significant insight into the mechanism of KGFR tumor suppression and suggest that KGFR gene therapy might be a viable method of inhibiting human salivary adenocarcinoma growth. K eratinocyte growth factor (KGF͞FGF7) is a member of the fibroblast growth factor (FGF) family (1). Its activity is largely restricted to epithelial cells, which express the KGF receptor (KGFR), a transmembrane tyrosine kinase encoded by the IIIb splice variant of FGFR2 (FGFR2-IIIb) (2, 3). KGFR binds KGF and FGF-1 with high affinity. In contrast, FGFR2-IIIc, another splice variant of FGFR2, binds FGF-1 and FGF-2, but not KGF (3, 4). Analysis of KGF and KGFR expression during embryonic development, including that of mammary glands, has provided evidence that KGF is an important mesenchymal mediator of epithelial growth and differentiation. In normal human skin, KGFR immunostaining localizes to the suprabasal layers (5, 6). The lack of KGFR in basal cell progenitors in skin suggests that KGFR might regulate keratinocyte differentiation (7).Malignant salivary tumors are highly aggressive neoplasms that readily invade adjacent tissues and metastasize to distant organs at early stages of the disease. Malignant salivary tumors exhibit enhanced expression of both FGF-1 and FGF-2 compared with normal salivary gland (8). FGF-1 and FGF-2 can act in an autocrine manner to stimulate the proliferation of salivary adenocarcinoma cells (8,9). Normal salivary gland epithelial cells and benign salivary gland tumors exclusively express the KGFR gene. During the malignant transformation of salivary gland epithelial cells, the expression of the KGFR gene is abolished, whereas the FGFR1-IIIc and FGFR4 genes are activated (10). The exclusive expression of the KGFR gene in both normal and premalignant salivary epithelial cells correlates well with the slow-growing and differentiated phenotype of premalignant tumors. In contrast, the loss of the KGFR gene and the expression of both the FGFR1 gene and its specific ligand FGF-2 in malignant tumor cells are associated with the emergence of the malignant phenotype. Thus, the loss of normal KGFR gene function may promote tumorigenicity, whereas KGFR may function to suppress human salivary adenocarcinomas.The Ras-MAP kinase signaling pathway plays...

Inhibition of human bladder tumour cell growth by fibroblast growth factor receptor 2b is independent of its kinase activity. Involvement of the carboxy-terminal region of the receptor

“…Growth inhibition is probably independent of kinase activity in the mouse prostatic tumour model, as growth inhibition was observed in the absence of receptor activation due to dimerization (Freeman et al, 2003). However, in contrast to what is , in the rat prostate tumour model and in HSY cells, growth inhibition is observed in the absence of ligand but is stronger if exogenous ligand is added (Matsubara et al, 1998, Zhang et al, 2001.…”

“…Thus, depending on the type of cell, FGFR2b exerts various tumour suppressive properties. Indeed, in rat prostatic carcinoma cells, FGFR2b inhibits proliferation and induces differentiation; in salivary carcinoma cells (HSY cells), FGFR2b induces differentiation and apoptosis, and was recently shown to inhibit the growth of mouse prostatic carcinoma cells in vivo but not in vitro (Feng et al, 1997;Matsubara et al, 1998;Zhang et al, 2001;Freeman et al, 2003). It would therefore be interesting to investigate, in these models, whether the various tumour suppressor effects induced by FGFR2b are also due to the downregulation of IGF-II, dependent on the C-terminal part of the receptor, and independent of receptor kinase activity, as in the bladder tumour cell line.…”

“…The expression of FGFR2b is reduced in human salivary adenocarcinoma , in prostate tumour epithelial cells (Feng et al, 1997;Matsubara et al, 1998, Naimi et al, 2002 and in transitional cell bladder carcinoma, in which this loss of FGFR2b expression is associated with a poor prognosis (Diez de Medina et al, 1997). Studies in vitro have confirmed that FGFR2b has tumour suppressor properties as this receptor inhibits the growth of prostate tumour cells (Feng et al, 1997, Matsubara et al, 1998, human urothelial carcinoma cells and human salivary adenocarcinoma cells (Zhang et al, 2001). FGFR2b inhibits the growth of human salivary adenocarcinoma cells by inducing differentiation and apoptosis.…”

Estrogen receptor-associated expression of keratinocyte growth factor and its possible role in the inhibition of apoptosis in human breast cancer

“…26 In human salivary gland tumors, loss of KGFR expression was observed in the process of malignant transformation. 50,51 Similarly, in prostate cancer, loss of KGFR expression was accompanied by the switch from androgen-sensitive, slow-growing tumors to androgen-insensitive, more aggressive tumors. 52 Therefore, KGF may play a pivotal role in the regulation of cell kinetics.…”

Directionally Specific Paracrine Communication Mediated by Epithelial FGF9 to Stromal FGFR3 in Two-Compartment Premalignant Prostate Tumors

“…Whereas isolated cell-free FGFR2IIIb-heparin complexes bind FGF2 significantly, a dependence on stromal FGF7 and FGF10 is set by epithelial cell heparan sulfate that, when complexed to FGFR2IIIb, prevents the binding of FGF2 (5,10,11). Stromal to epithelial cell signaling via FGF7/FGF10 and FGFR2IIIb has a net effect of promoting epithelial cell homeostasis that includes growth but limits population growth overall by feedback inhibition mechanisms and induction of differentiation (7,8,(12)(13)(14)(15)(16)(17). Subversion of the strict directional instruction from stroma to epithelium mediated by the FGF7/FGF10 and FGFR2IIIb system at multiple steps and acquisition of an autocrine signaling loop by ectopic activation of FGF family members in epithelium and stroma that are unrestrained in respect to growth are hallmarks of the progression of premalignant prostate tumor epithelial cells to malignancy (1).…”