Negative Regulation of p53-Induced Senescence by N-WASP Is Crucial for DMBA/TPA-Induced Skin Tumor Formation

Abstract

Mice with a keratinocyte-restricted deletion of the actin polymerization-promoting molecule, N-WASP, display cyclic hair loss and skin inflammation. Here, we showed that these mice were also resistant to 7,12-dimethylbenz(a) anthracene (DMBA)/12-O-tetradecanoylphorbol-13-acetate (TPA)-induced skin tumor formation. This resistance correlated with decreased expression of the senescence regulator, DNMT1, and increased expression of the senescence marker, p16Ink4a, in N-WASP-deficient epidermis. Moreover, primary N-WASP-null keratinocytes displayed a premature senescence phenotype in vitro. Expression and activation of p53, a major inducer of senescence, was not significantly altered in N-WASP-null keratinocytes. However, impairment of p53 function effectively rescued the senescence phenotype, indicating that N-WASP was an inhibitor of p53-induced senescence. Mechanistically, N-WASP regulated senescence by preventing p53-dependent degradation of the H3K9 methyltransferases, G9a/GLP, and the DNA methyltransferase, DNMT1, which both control keratinocyte senescence. This pathway collaborated with other N-WASP-independent, senescence-promoting signaling downstream of p53 and allowed the fine tuning of p53induced senescence by N-WASP. Collectively, these data reveal N-WASP as an inhibitor of p53-induced senescence, which might be of importance for skin tumor formation and cellular aging of keratinocytes.Significance: These findings demonstrate that N-WASP regulates p53-dependent senescence in keratinocytes in vitro and in vivo. Gene expression analysisRNA from skin and keratinocytes culture was prepared using the GeneElute Mammalian Total RNA Miniprep Kit (RNT350, Sigma) according to the instructions of the manufacturer. Skin Li et al.

Loss of Wasl improves pancreatic cancer outcome

“…Loss of Wasl leads to delocalization of N-WASP protein binding partners. Nuclear N-WASP has recently been linked to regulation of senescence (10). However, no nuclear N-WASP staining was observed in CKP and CKP-N het tumors (Figure 2A).…”

“…We further showed that this ADM is dependent on the neural Wiskott-Aldrich syndrome protein (N-WASP, encoded by the Wasl gene). N-WASP is an indicator of poor prognosis in several cancers and has been implicated in the regulation of metastasis via the promotion of cell migration and remodeling of the extracellular matrix (6)(7)(8)(9)(10)(11). At the cellular level, N-WASP interacts with components of the actin cytoskeleton, including the ARP2/3 complex and CDC42, as well as with PIP2 (12,13).…”

Involvement of Actin and Actin-Binding Proteins in Carcinogenesis

“…WASP may also be involved in the regulation of RNA polymerase II activity [ 88 ]. Additionally, the correlation between WASP and the p53/p21 signaling pathway also plays an important role in carcinogenesis [ 89 ], whereas the relationship between N-WASP and oncogenic KRas was observed in pancreatic ductal adenocarcinoma [ 90 ].…”

Senescence regulation by nuclear N-WASP: a role in cancer?

“…We could show now that nuclear N-WASP regulates also senescence in keratinocytes and keratinocyte stem cells and thus influences chemically induced skin tumor formation in mice [6]. Mice with a keratinocyte-restricted deletion of the N-WASP gene show increased senescence marks in skin including increased expression of the cell cycle inhibitor p16Ink4a, decreased expression of the DNA maintenance methyltransferase DNMT1, and increased size and granularity of keratinocytes, particularly of the stem cells.…”

“…Mechanistical analysis revealed further that nuclear N-WASP binds to the histone methyltransferases G9a/GLP and to the DNA methyltransferase DNMT1, which inhibits the proteolytic degradation of these epigenetic regulators, leading to reduced levels of G9a/GLP and DNMT1 in N-WASP ko cells [6,7]. Interestingly, DNMT1 itself can bind to G9a/GLP [8], but also to β-catenin [9], a crucial transcription factor for keratinocyte stem cells which is required for the formation and maintenance of DMBA/TPA induced skin tumor [10].…”