Abrogation of protein phosphatase 6 promotes skin carcinogenesis induced by DMBA

Abstract

Somatic mutations in the gene encoding the catalytic subunit of protein phosphatase 6 (Ppp6c) have been identified in malignant melanoma and are thought to function as a driver in B-raf- or N-ras-driven tumorigenesis. To assess the role of Ppp6c in carcinogenesis, we generated skin keratinocyte-specific Ppp6c conditional knockout mice and performed two-stage skin carcinogenesis analysis. Ppp6c deficiency induced papilloma formation with 7,12-dimethylbenz (a) anthracene (DMBA) only, and development of those papillomas was significantly accelerated compared with that seen following DMBA/TPA (12-O-tetradecanoylphorbol 13-acetate) treatment of wild-type mice. NF-κB activation either by tumor necrosis factor (TNF)-α or interleukin (IL)-1β was enhanced in Ppp6c-deficient keratinocytes. Overall, we conclude that Ppp6c deficiency predisposes mice to skin carcinogenesis initiated by DMBA. This is the first report showing that such deficiency promotes tumor formation in mice.

Loss of protein phosphatase 6 in mouse keratinocytes increases susceptibility to ultraviolet-B-induced carcinogenesis

“…We found that a single 7,12-dimethylbenz(a)anthracene (DMBA) application was sufficient to produce papillomas in Ppp6c-deficient skin and showed that tumor promotion associated with Ppp6c-deficiency is more robust than that seen after repeated applications of a typical tumor promoter such as TPA. As such, ours was the first report that Ppp6c loss-offunction acts as a tumor promoter in mice [17]. However, it remained unclear whether tumor promotion (1) is specific to DMBA as an initiator or (2) is limited to papilloma or carcinoma formation.…”

“…Mice exhibiting epidermal-specific, inducible Ppp6c deficiency (K14-CreER tam ; Ppp6c flox/flox ) were generated as described [17]. In brief, K14-CreER tam mice were crossed with Ppp6c-floxed (Ppp6c flox/flox ) mice (Accession No.…”

“…Cell lysate preparation and immunoblot analysis were performed as described [17]. Proteins of interest were assessed using anti-p53 (Cell Signaling Technology Inc.), anti-PUMA and anti-BAX (both from Santa Cruz Biotechnology Inc.), anticleaved caspase-3 (Cell Signaling Technology Inc.), and anti-tubulin-HRP (MBL, Nagoya, Japan) antibodies.…”

“…Images were acquired using an Olympus BX53 microscope (Tokyo, Japan). Immunohistochemistry (IHC) was performed as described [17] using anti-γH2AX, antip53 and Ki-67 antibodies (Cell Signaling Technology Inc., Danvers, MA, USA) and anti-p21 antibody (Santa Cruz Biotechnology Inc.).…”

“…Recently, to determine whether PP6 deficiency functions in carcinogenesis in vivo, we employed a mouse skin 2-stage carcinogenesis model [17]. We found that a single 7,12-dimethylbenz(a)anthracene (DMBA) application was sufficient to produce papillomas in Ppp6c-deficient skin and showed…”