Human keratin-1.bcl-2 transgenic mice aberrantly express keratin 6, exhibit reduced sensitivity to keratinocyte cell death induction, and are susceptible to skin tumor formation

Abstract

Nonmelanoma skin cancers (NMSC) are among the most common malignancies in the world. Typically, these neoplasms grow slowly and are comparatively indolent in their clinical behavior. The most frequent molecular alterations implicated in the pathogenesis of these neoplasms involve genes known to be regulators of cell death including p53, Ha-ras and bcl-2. In order to evaluate the signi®cance cell death deregulation during skin carcinogenesis, we generated a transgenic mouse model (HK1.bcl-2) using the human keratin 1 promoter to target the expression of a human bcl-2 minigene to the epidermis. Transgenic HK1.bcl-2 protein was expressed at high levels speci®cally in the epidermis extending from the stratum basale through the stratum granulosum. The epidermis of HK1.bcl-2 mice exhibited multifocal hyperplasia without associated hyperkeratosis and aberrant expression of keratin 6. The rate of proliferation was similar in HK1.bcl-2 and control epidermis although suprabasal BrdUrd incorporating cells were present only in HK1.bcl-2 skin. Keratinocytes from the HK1.bcl-2 mice were signi®cantly more resistant to cell death induction by U.V.-B, DMBA, and TPA, compared to control keratinocytes. Furthermore, papillomas developed at a signi®cantly greater frequency and shorter latency in the HK1.bcl-2 mice compared to control littermates following initiation with DMBA and promotion with TPA. Together these results support a role for bcl-2 in the pathogenesis of NMSC.

Alterations in cell death and cell cycle progression in the UV-irradiated epidermis of bcl-2-deficient mice

“…9,24 Consistently, a decrease in the number of apoptotic keratinocytes (`sunburn cells') by approximately 50% has been reported after UV-B exposure of bcl-2 transgenic mice or bcl-2 overexpressing keratinocyte cultures. 7,14 In our bcl-2 7/7 mice the number of epidermal cells showing DNA fragmentation did not differ from wild-type littermates at 6 h after UV-B, whereas at 24 h the number of TUNEL-positive keratinocytes was much higher in bcl-2-deficient animals. The similar rate of early UV-induced cell death in wild-types and null mutants may be attributed to the higher dose of UV radiation applied in vivo.…”

“…In bcl-2 transgenic mice epidermal cell death under physiological conditions is unaltered as well. 14 On the other hand, the response of epidermal cells to genotoxic stress is influenced by the level of >bcl-2 expression. Following UV-B irradiation expression of bcl-2 in epidermal keratinocytes and melanocytes is rapidly down-regulated, 7,13,23 which according to current concepts lowers the threshold for apoptosis.…”

“…7,13 Targeted expression of human bcl-2 in the epidermis of transgenic mice prevents apoptotic death of keratinocytes after UV-B exposure strongly suggesting a functional role for Bcl-2 in epidermal cell death after genotoxic stress. 14 Additionally, three lines of bcl-2-deficient mice have been reported which develop similar phenotypic abnormalities after birth, including hair hypopigmentation, suggesting that bcl-2 may also be essential for melanocyte function or maintenance under physiological conditions. 15±17 In the present study, we investigated the effects of bcl-2 gene-ablation in mice on UV-induced epidermal cell death in vivo and in vitro.…”

Inhibition of Bcl-xL expression sensitizes normal human keratinocytes and epithelial cells to apoptotic stimuli

“…The role of Bcl-2 and Bcl-x L in skin development, di erentiation and apoptosis has been analysed by generating transgenic mice that overexpress these proteins in the epidermis (RodriguezVillanueva et al, 1998;Pena et al, 1997Pena et al, , 1998. The skin from mice expressing a keratin-1 driven Bcl-2 transgene exhibited increased proliferation and the keratinocytes from these mice were signi®cantly more resistant to cell death induction by UV radiation, DMBA and TPA (Rodriguez-Villanueva et al, 1998). In mice containing a keratin-14 driven Bcl-x L transgene, skin cells also showed a dramatic increase in resistance to UV irradiation (Pena et al, 1997).…”

Bcl-2 expression delays mammary tumor development in dimethylbenz(a)anthracene-treated transgenic mice

“…It is a member of a family of known cell death regulators, and can function to suppress or delay the induction of apoptosis in a number of systems, including prostate (Beham et al, 1997), skin (Rodriguez-Villanueva et al, 1998), lymphoid tissues (Strasser et al, 1994), and mammary gland (JaÈ ger et al, 1997;Lu et al, 1995). This dysregulation of apoptosis may lead to pathological disorders involving cell accumulation, including cancer.…”