Conditional knockout ARL6ip5 enhances dimethylbenz[a]anthracene induced DNA damage but suppresses phorbol ester triggered skin papillomas in mice

Abstract

ARL6ip5, also called JWA and GTRAP3-8, as an active environmental responsive gene has been extensively studied. Our previous studies indicated that ARL6ip5 via differential signal pathways plays important roles in DNA damage repair, cell migration, and tumor metastasis, respectively. In this study, we designed a two-stage model of skin carcinogenesis to investigate the role of ARL6ip5 in chemical carcinogenesis using conditional knockout mice. Both wild type and knockout mice were used in this DMBA/TPA two-stage papilloma induction assay. The mice dorsal skin was treated topically with 25 μg of DMBA 100 μl acetone once. One week later, each animal received subsequent topical treatments of 2.5 μg of TPA in 100 μl acetone twice a week for 19 weeks. The results indicated that ARL6ip5 knockout mice were resistant to the development of skin papillomas initiated by DMBA followed by promotion with TPA. In ARL6ip5 knockout mice, the induction of papilloma was delayed, and the tumor number and size were reduced. However, DMBA exposure induced more intensive DNA damage in primary keratinocytes from ARL6ip5 knockout mice, while TPA-promoted cell proliferation was reduced. The further mechanistic studies showed that ARL6ip5 deficiency blocked TPA-induced activation of MAPKs and its downstream transcription factor Elk1 both in vitro and in vivo. These results suggest the importance of ARL6ip5 in maintaining skin cellular homeostasis and in the process of skin tumor development.
Key words: ARL6ip5; JWA; DMBA/TPA; skin papillomas; MAPK; Elk1