Role of ß-TrCP ubiquitin ligase receptor in UVB mediated responses in skin.

Skin cancers are the most common cancers in the United States. Exposure to UVB radiation is a major risk factor for skin cancer induction. SCF(ß-TrCP) E3 ubiquitin ligase has been found to be involved in cell cycle, cell proliferation and transformation. Aberrant up-regulation of beta-transducin repeats-containing proteins (ß-TrCP) is often found in cancer cell lines and primary tumors. We have previously demonstrated that ß-TrCP2 is over-expressed in chemically induced mouse skin tumors. Various cellular stress stimuli, including UVB, induce an increase in ß-TrCP1 mRNA and protein levels in human cells. We have previously shown that inhibition of ß-TrCP function, by induction of dominant negative ß-TrCP2 (ß-TrCP2(ΔF)), in vitro in hTERT immortalized normal keratinocytes, results in increase in UVB induced apoptosis. We have generated transgenic mice with inducible, selective expression of dominant negative ß-TrCP2 in epidermis with the Keratin 5 promoter (K5-rTA x TRE-HA-ß-TrCP(ΔF)). Here we report that inhibition of ß-TrCP function in mouse epidermis results in decrease in UVB-induced edema, hyperplasia, and inflammatory response and increment in UVB-induced apoptosis in skin. Our results suggest that ß-TrCP may be an essential player in UVB induced responses in skin and can be a potential therapeutic target for skin cancer.

Inhibition of beta-TrCP function potentiates UVB-induced apoptosis in hTERT-immortalized normal human keratinocytes.

Chronic skin exposure to UV radiation manifests in a score of biochemical events, DNA damage and mutations which can potentially cause skin cancer. The ubiquitin proteasome pathway controls the degradation of a majority of regulatory eukaryotic proteins including those which play a key role in tumorigenesis. SCFbetaTrCP E3 ubiquitin ligases mediate ubiquitination and proteasomal degradation of phosphorylated substrates that play a key role in signal transduction. Activation of several signaling pathways involved in tumorigenesis was shown to elevate expression and activity of beta-TrCP1/2. In this study, we established and characterized human neonatal foreskin keratinocytes, rendered immortal by retroviral introduction of human telomerase reverse transcriptase (hTERT). These skin hTERT immortalized normal keratinocytes (STINKs) maintain characteristic traits of keratinocytes, such as expression of keratins, cytoplasmic localization of basonuclin and susceptibility to high concentration of calcium. We analyzed the response of STINKs to UVB radiation and its classical markers, such as p53 and nuclear factor (NF)-kappaB. We also demonstrate that inhibition of beta-TrCP2 function, by induction of dominant negative beta-TrCP2 (beta-TrCP2DeltaN), accentuates UVB induced apoptosis, and this phenomenon is independent of NF-kappaB and p53 pathways.