Kinetics of wound-induced v-Ha-ras transgene expression and papilloma development in transgenic Tg.AC mice

Abstract

The Tg.AC transgenic mouse, which harbors an activated v-Ha-ras coding region that is fused to an embryonic zeta globin transcriptional control region and a 3' simian virus 40 polyadenylation sequence, rapidly develops epidermal papillomas in response to topical application of chemical carcinogens or tumor promoters or to full-thickness wounding of the dorsal skin. In this report, we investigated the localization and temporal induction of v-Ha-ras transgene expression after full-thickness wounding of Tg.AC mouse skin. Surgically inflicted full-thickness incisions 3 cm long yielded four to six papillomas per Tg.AC mouse by 5 wk after wounding. Similar wounding of the FVB/N isogenic host strain did not produce tumors, which implicates a causal role for the v-Ha-ras transgene. Reverse transcription-polymerase chain reaction assays detected the v-Ha-ras transgene transcript in total RNA samples isolated from wound-associated tissue 3 and 4 wk after wounding. Tissues 1-2 wk after wounding and all non-wound-associated tissues were negative for transgene expression. In situ hybridization experiments using transgene-specific 35S-labeled antisense RNA probes localized transgene expression to the basal epidermal cells in wound-induced papillomas. Adjacent normal and hyperplastic skin tissues were negative for transgene expression by this assay. This work supports the hypothesis that the wound repair response leads to the transcriptional activation and continued expression of the v-Ha-ras transgene in specific cells in the skin, which alters normal epithelial differentiation and ultimately results in neoplastic growth.

Biological, cellular, and molecular characteristics of an inducible transgenic skin tumor model: a review

“…In the absence of additional signaling, neoplastic proliferation does not occur. In most cases, using whole skin, the earliest transgene expression detected is 18 days following the first of four TPA treatments (Hansen and Tennant, 1994a) or 16 days after a full-thickness wound (Cannon et al, 1997), concomitant with global hypomethylation . However, using keratinocytes harvested from TPA-treated skin, it has been shown that the transgene can be detected by RT-PCR 14 days after treatment with TPA in older, more responsive mice, and as early as 9 days after TPA treatment using fractionated keratinocytes (Battalora et al, 2001).…”

“…A variety of stimuli have been shown to affect gene expression by altering CpG methylation (reviewed in Cannon et al, 1998). The methylation status of the Tg.AC transgene was examined over the time course of wound-induced papillomagenesis (Cannon et al, 1997). A site-specific hypomethylation of the transgene is detectable by DNA blots 23 days after wounding .…”

“…Topical exposure to tumor promoters (Leder et al, 1990;Spalding et al, 1993), chemical carcinogens , UV light (Trempus et al, 1998a; Chignell et al, 2003a), full-thickness surgical wounding (Cannon et al, 1997), and depilation (Hansen and Tennant, 1994b) all result in epidermal hyperplasia. Within that hyperplasia, expression of the transgene in specific cells drives clonal expansion and tumor formation.…”

IL-1α, Innate Immunity, and Skin Carcinogenesis: The Effect of Constitutive Expression of IL-1α in Epidermis on Chemical Carcinogenesis

“…To investigate further, K14/IL-1␣ mice were cross-bred to the TG.AC Tg strain that constitutively expresses an activated Ha-ras gene (20). These mice develop carcinomas after cutaneous injury or TPA promotion without prior DMBA initiation (20,22,23) and are thus sometimes referred to as preinitiated mice. If the resistance to two-stage carcinogenesis observed for the K14/IL-1␣ mice was due to failed initiation, then expression of the IL-1␣ transgene in TG.AC mice was predicted to reverse this effect.…”

12-O-Tetradecanoylphorbol-13-acetate and UV Radiation-induced Nucleoside Diphosphate Protein Kinase B Mediates Neoplastic Transformation of Epidermal Cells

“…The molecular changes associated with the early stages of skin tumor formation have yet to be determined. Tg⅐AC mice, which carry the coding region of the v-Ha-ras oncogene fused to a fetal -globin gene promoter (3), are considered to be genetically initiated and have a higher sensitivity to promotional stimuli including TPA 1 (3) and full thickness wounding (4), or carcinogens such as UV radiation (UVR) (5) and 7,12-dimethylbenz[a]anthracene (6). These features establish the in vivo Tg⅐AC mouse model as a valuable tool to study the early stages of skin carcinogenesis.…”