Diverse tumorigenesis associated with aberrant development in mice overexpressing hepatocyte growth factor/scatter factor

Abstract

Hepatocyte growth factor/scatter factor (HGF/SF) is a mesenchymally derived, multifunctional paracrine regulator possessing mitogenic, motogenic, and morphogenetic activities in cultured epithelial cells containing its tyrosine kinase receptor, Met. c-met has been implicated in oncogenesis through correlation of expression with malignant phenotype in specific cell lines and tumors. Paradoxically, however, HGF/SF can also inhibit the growth of some tumor cells. To elucidate the oncogenic role of HGF/SF in vivo, transgenic mice were created such that HGF/SF was inappropriately targeted to a variety of tissues. HGF/SF transgenic mice developed a remarkably broad array of histologically distinct tumors of both mesenchymal and epithelial origin. Many neoplasms arose from tissues exhibiting abnormal development, including the mammary gland, skeletal muscle, and melanocytes, suggesting a functional link between mechanisms regulating morphogenesis and those promoting tumorigenesis. Most neoplasms, especially melanomas, demonstrated overexpression of both the HGF/SF transgene and endogenous c-met, and had enhanced Met kinase activity, strongly suggesting that autocrine signaling broadly promotes tumorigenesis. Thus, subversion of normal mesenchymal-epithelial paracrine regulation through the forced misdirection of HGF/SF expression induces aberrant morphogenesis and subsequent malignant transformation of cells of diverse origin.

Figures

Figure 1

Aberrant morphogenesis and oncogenesis in HGF/SF transgenic mice. (A) Primary malignant amelanotic melanoma that metastasized widely. Note whorling pattern and multiple mitotic figures (arrow). (B) Electron micrograph of a melanoma cell with numerous melanosomes (arrowhead indicates a cluster). (C) Rhabdomyosarcoma that arose in the skin; note multiple mitotic figures (arrow). (D) Strong HGF/SF staining in a liver tumor (t) relative to adjacent tissue (a). (E) Characteristic mammary adenosquamous carcinoma composed of both mammary and hair follicle elements. (F) Precocious development in transgenic virgin females of alveolar structures (arrow), which expressed casein and whey acidic protein (G. Smith and G.M., unpublished data). (G) Normal ducts in nontransgenic virgin females. (H) Olfactory adenocarcinoma (t), which obliterated one side of the nasal olfactory mucosa; unaffected but disorganized olfactory mucosa is indicated by the arrow. (I) Higher magnification of the disorganized transgenic olfactory mucosa with degenerated epithelium, marked hypertrophy and hyperplasia of glands, and depleted nerves. Malformation of the nerves was confirmed by immunohistochemical staining using an antibody to S-100 (data not shown). (J) Nontransgenic olfactory mucosa. (A and C, ×400; B, ×39,500; D, F, and G, ×200; E, ×100; H, ×25; I and J, ×630.)

Figure 2

Molecular and biochemical analyses of HGF/SF and c-met in transgenic neoplasms. (A) Northern blot detection of transgenic HGF/SF (Upper) and c-met (Lower) RNA transcripts in tumors and normal tissue. Migration of 28S and 18S rRNAs are shown at left. (B) Quantification of Met protein by anti-Met immunoprecipitation followed by anti-Met immunoblotting (Upper) and Met kinase activity by anti-phosphotyrosine (PY) immunoprecipitation followed by anti-Met immunoblotting (Lower). Location of p140 and p170 forms of Met are shown at left. Note greatly enhanced kinase activity associated with rhabdomyosarcoma 70. Normal tissues: wtMa, wild-type mammary; wtSkM, wild-type skeletal muscle; tgLi, transgenic liver; tgMa, transgenic mammary. Neoplasms: HaFo, hair follicle tumor; Hem, hemangiosarcoma; Mamm, mammary tumors; Melano, melanoma; Fibro, fibrosarcoma; LiAd, liver adenoma; Rhab, rhabdomyosarcoma; SaAc, salivary adenocarcinoma. The 1p, 1r, and 1m labels designate samples from primary, recurrent (following resection), and metastatic melanoma number 1. (C) Amplification of c-met DNA in overexpressing rhabdomyosarcoma 70 (lane b), but not in overexpressing mammary adenocarcinoma 4 (lane c). (Lane a) Unamplified c-met sample. Numbers throughout identify specific tumors (see Table 2).