Tumorigenic conversion of immortal human keratinocytes through stromal cell activation

Abstract

The stromal microenvironment plays a crucial role in tumor development and progression. One of the most potent activators of stromal cells is the platelet-derived growth factor (PDGF). To investigate the role of PDGF in epithelial tumor development we stably transfected immortal nontumorigenic human keratinocytes with the PDGF-B cDNA. Transfected HaCaT cells overexpressed PDGF-B but remained negative for the PDGF receptors ␣ and ␤ (mRNA). Thus, they did not exhibit autocrine growth stimulation in vitro, but proliferation of cocultured fibroblasts was enhanced and this effect was inhibited by a neutralizing antibody to PDGF-BB. After subcutaneous injection into nude mice the transfected cells maintained high PDGF expression and formed progressively enlarging, rapidly proliferating cysts, classified as benign tumors. During early tumor development (up to 2 months), PDGF-B transfectants induced marked mesenchymal cell proliferation and angiogenesis, yet this effect vanished at later stages (2-6 months) concomitantly with increased epithelial cell proliferation and enhanced tumor growth. These results demonstrate that an activated stromal environment can promote tumorigenic conversion of nontumorigenic keratinocytes by inducing sustained epithelial hyperproliferation. This effect is apparently caused by a dual action of PDGF-BB: (i) PDGF-BB can promote tumor growth by inducing angiogenesis and stroma formation, and (ii) PDGF-activated stromal cells maintain elevated keratinocyte proliferation via a paracrine mechanism. Thus, PDGF, a major factor activated in wound healing, may play an important role as an endogenous promoter in epithelial tumor formation.

UVA radiation causes DNA strand breaks, chromosomal aberrations and tumorigenic transformation in HaCaT skin keratinocytes

“…These cells represent an early stage of skin carcinogenesis because they harbor UVB type-specific p53 mutations (Lehman et al, 1993) as well as some chromosomal abnormalities typical for human skin SCCs (Lehman et al, 1993;Boukamp et al, 1997;Popp et al, 2002). While the HaCaT cells remained nontumorigenic through long-term passaging, they became tumorigenic by transduction with the Harvey-ras oncogene, increased temperature or stroma modulating growth factors known to be relevant for tumorigenicity (Boukamp et al, 1990b(Boukamp et al, , 1995(Boukamp et al, , 1997Skobe and Fusenig, 1998;Obermueller et al, 2004). Thus, the intrinsic stable nontumorigenic phenotype, together with the sensitivity for tumorigenic conversion upon distinct changes, make HaCaT cells a highly suitable model to study the role of UVA in skin carcinogenesis.…”

Tumour-derived TGF-β1 modulates myofibroblast differentiation and promotes HGF/SF-dependent invasion of squamous carcinoma cells

“…Several other paracrine interactions between keratinocytes and fibroblasts have been demonstrated previously. For example, it has been suggested that PDGF-activated stromal cells maintain elevated keratinocyte proliferation via a paracrine mechanism (Skobe andFusenig, 1998), andMaas-Szabowski et al (2001) showed that IL-1 produced by epidermal keratinocytes induced the expression of KGF by dermal fibroblasts, which in turn stimulated keratinocyte proliferation. Paracrine interactions have also been demonstrated between squamous carcinoma cells and other cell types.…”

“…Maas-Szabowski et al (2001) showed that IL-1 produced by epidermal keratinocytes induced the expression of keratinocyte growth factor by dermal fibroblasts, which in turn stimulated keratinocyte proliferation. It has also been suggested that PDGF-activated stromal cells may maintain elevated keratinocyte proliferation via a paracrine mechanism (Skobe and Fusenig, 1998). Ramos et al (1997) demonstrated that peritumour fibroblast-conditioned medium promoted SCC migration on tenascin, and that this effect could be partially inhibited by blocking EGF, TGF-b1 or hepatocyte growth factor/scatter factor (HGF/SF).…”

Aging, tumor suppression and cancer: high wire-act!

“…Moreover, senescent fibroblast can stimulate the tumorigenic conversion of premalignant epithelial cells into frankly malignant tumors in vivo (Krtolica et al, 2001). The phenotype of senescent fibroblasts, described above, strongly resembles that of ''activated stroma'' or carcinoma-associated fibroblasts, both which have been shown to strongly stimulate tumor progression in cell culture models and in vivo (Skobe and Fusenig, 1998;Olumi et al, 1999;Shekhar et al, 2001;Martens et al, 2003). Interestingly, irradiated fibroblasts, which were likely senescent albeit not explicitly characterized as such, were also shown to promote epithelial tumor progression in vivo (Barcellos-Hoff and Ravani, 2000).…”

“…In many of these cases, the cancer-promoting activity of the senescent or activated stroma was due at least in part to their secretory phenotype (Skobe and Fusenig, 1998;Olumi et al, 1999;Krtolica et al, 2001;Shekhar et al, 2001;Martens et al, 2003;Parrinello et al, submitted for publication). Thus, the age-dependent accumulation of senescent cells, particularly senescent stromal cells, may synergize with the age-dependent accumulation of mutations, resulting in the rise in epithelial cancers.…”