p53 and the pathogenesis of skin cancer

Thymoma associated with malignancies may herald a hereditary cancer syndrome

Two probands with thymoma and other primary malignancies with multiple cancer patients in the family are described. Types of malignancies, pattern of pedigree and age of the patients do not match the known familial cancer syndromes. One proband was a very rare case with five discrete primary malignancies; TP53 sequencing and karyotyping did not reveal any mutations. These cases suggest thymoma associated malignancies may herald a hereditary cancer syndrome.

Absence of p53-dependent apoptosis leads to UV radiation hypersensitivity, enhanced immunosuppression and cellular senescence

Genotoxic stress triggers the p53 tumor suppressor network to activate cellular responses that lead to cell cycle arrest, DNA repair, apoptosis or senescence. This network functions mainly through transactivation of different downstream targets, including cell cycle inhibitor p21, which is required for short-term cell cycle arrest or long-term cellular senescence, or proapoptotic genes such as p53 upregulated modulator of apoptosis (PUMA) and Noxa. However, the mechanism that switches from cell cycle arrest to apoptosis is still unknown. In this study, we found that mice harboring a hypomorphic mutant p53, R172P, a mutation that abrogates p53-mediated apoptosis while keeping cell cycle control mostly intact, are more susceptible to ultraviolet-B (UVB)-induced skin damage, inflammation and immunosuppression than wild-type mice. p53(R172P) embryonic fibroblasts (MEFs) are hypersensitive to UVB and prematurely senesce after UVB exposure, in stark contrast to wild-type MEFs, which undergo apoptosis. However, these mutant cells are able to repair UV-induced DNA lesions, indicating that the UV hypersensitive phenotype results from the subsequent damage response. Mutant MEFs show an induction of p53 and p21 after UVR, while wild-type MEFs additionally induce PUMA and Noxa. Importantly, p53(R172P) MEFs failed to downregulate anti-apoptotic protein Bcl-2, which has been shown to play an important role in p53-dependent apoptosis. Taken together, these data demonstrate that in the absence of p53-mediated apoptosis, cells undergo cellular senescence to prevent genomic instability. Our results also indicate that p53-dependent apoptosis may play an active role in balancing cellular growth.

A p38(MAPK)/HIF-1 pathway initiated by UVB irradiation is required to induce Noxa and apoptosis of human keratinocytes

The signal transduction pathways leading to apoptosis of human keratinocytes responding to UVB irradiation are complex and not completely understood. Previously, we reported that in UVB-irradiated keratinocytes, p38(MAPK) instigates Bcl-2-associated X protein (Bax) activation and mitochondrial apoptosis. However, the molecular mechanism underlying the pro-apoptotic function of p38(MAPK) remained unclear. Here, we show that in UVB-treated human primary keratinocytes the activation of p38(MAPK) is necessary to upregulate Noxa, a BH3-only pro-apoptotic dominantly induced by UVB and required for apoptosis. Whereas p53-silencing was marginally cytoprotective and poorly affected Noxa expression, p38(MAPK) inhibition in p53-silenced keratinocytes or in p53(-/-) cells could still efficiently prevent Noxa induction and intrinsic apoptosis after UVB, indicating that p38(MAPK) signals mainly through p53-independent mechanisms. Furthermore, p38(MAPK) was required for the induction and activation of hypoxia-inducible factor 1 (HIF-1) in response to UVB, and HIF-1 knockdown reduced Noxa expression and apoptosis. In UVB-irradiated keratinocytes, Noxa targeted the anti-apoptotic myeloid cell leukemia sequence 1 (Mcl-1) for degradation, and small-interfering RNA (siRNA)-mediated knockdown of Noxa or p38(MAPK) inhibition restored levels of Mcl-1 and abolished apoptosis. Thus, the pro-apoptotic mechanisms orchestrated by p38(MAPK) in human keratinocytes in response to UVB involve an HIF-1/Noxa axis, which prompts the downregulation of anti-apoptotic Mcl-1, thereby favoring Bax-mediated mitochondrial apoptosis of UVB-damaged keratinocytes.

Sebaceous neoplasia and the Muir-Torre syndrome: important connections with clinical implications

Sebaceous neoplasia comprises a spectrum ranging from benign to malignant. Proper histological identification is important for treatment, prognosis and potential association with the Muir-Torre syndrome (MTS). Our increased understanding of the significance and pathogenesis of these tumours has led to improved risk stratification, screening recommendations, and treatment of patients with an initial presentation of a sebaceous tumour. This review focuses on the diagnostic and histological features of sebaceous lesions, the MTS, and recent insights into the molecular pathogenesis of sebaceous tumours.

Non-melanoma skin cancer

The rising incidence and morbidity of non-melanoma skin cancers has generated great interest in unravelling of their pathogenesis and in the search for new non-invasive treatments. Whereas the role of cumulative sun exposure in pathogenesis of squamous-cell carcinoma seems clear, the relation between sun-exposure patterns and subtypes of basal-cell carcinoma remains undetermined. Several complex genotypic, phenotypic, and environmental factors contribute to pathogenesis of non-melanoma skin cancers. Unlike basal-cell carcinoma, squamous-cell carcinomas can arise from precursor lesions. Diagnosis of non-melanoma skin cancer is made clinically and confirmed by histological testing. Prognosis depends on lesion and host characteristics, which also dictate choice of treatment. Prevention strategies aim at reduction of sun exposure, but are of unproven benefit, especially for basal-cell carcinoma. Surgical excision with predetermined margins is the mainstay of treatment for squamous-cell carcinoma and for most basal-cell carcinomas. Of the new non-invasive treatments, only photodynamic therapy and topical imiquimod have become established treatments for specific subtypes of basal-cell carcinoma, and the search for more effective and tissue-salvaging therapies continues.

Multi-stage chemical carcinogenesis in mouse skin: fundamentals and applications

For more than 60 years, the chemical induction of tumors in mouse skin has been used to study mechanisms of epithelial carcinogenesis and evaluate modifying factors. In the traditional two-stage skin carcinogenesis model, the initiation phase is accomplished by the application of a sub-carcinogenic dose of a carcinogen. Subsequently, tumor development is elicited by repeated treatment with a tumor-promoting agent. The initiation protocol can be completed within 1-3 h depending on the number of mice used; whereas the promotion phase requires twice weekly treatments (1-2 h) and once weekly tumor palpation (1-2 h) for the duration of the study. Using the protocol described here, a highly reproducible papilloma burden is expected within 10-20 weeks with progression of a portion of the tumors to squamous cell carcinomas within 20-50 weeks. In contrast to complete skin carcinogenesis, the two-stage model allows for greater yield of premalignant lesions, as well as separation of the initiation and promotion phases.

Suberythemal ultraviolet B radiation alters the expression of cell cycle-related proteins in the epidermis of human subjects without leading to photoprotection

BACKGROUND

Deregulation of the cell cycle proteins is one of the critical factors leading to cutaneous carcinogenesis.

OBJECTIVES

To monitor the expression of cell cycle proteins in the epidermis of subjects after repeated exposure to ultraviolet (UV) B radiation, and to test for the development of photoprotection by subsequent irradiation with a single erythemal UVB dose.

METHODS

A total of 26 healthy volunteers were divided into four groups: group 1 (n = 9) were given whole-body UVB irradiation for 10 consecutive days with 0.7 minimal erythema dose (MED), group 2 (n = 9) were irradiated as in group 1 followed 24 h later by a single UVB dose of 3 MED on buttock skin, group 3 (n = 4) were irradiated with a UVB dose of 3 MED on buttock skin, and group 4 (n = 4) were not irradiated. Skin biopsies were collected 24 h after the final irradiation and stained for cyclins A, B1, D1, and p16, p18, p21, p27, p53, pRB, Bax and Bcl-2.

RESULTS

The expression of cyclin D1, p18 and p21 was significantly higher in groups 1 and 2 compared with the nonirradiated group 4 controls and, in group 2, the expression of pRB, p53 and Bax was also increased. In group 3, only p53 and Bax proteins were significantly elevated compared with group 4. The expression of cyclin D1, p16, p18, p27, pRB and Bcl-2 was higher in group 2 compared with group 3.

CONCLUSIONS

Suberythemal UVB radiation was sufficient to cause changes in the expression of several epidermal cell cycle proteins. When tested by irradiation with a single erythemal UVB dose following the repeated exposures, no photoprotection against the UV-induced alteration in cell cycle protein expression was apparent.

Implications of endoplasmic reticulum stress, the unfolded protein response and apoptosis for molecular cancer therapy. Part I: targeting p53, Mdm2, GADD153/CHOP, GRP78/BiP and heat shock proteins

BACKGROUND

In eukaryotes, endoplasmic reticulum stress (ERS) and the unfolded protein response (UPR) are coordinately regulated to maintain steady-state levels and activities of various cellular proteins to ensure cell survival.

OBJECTIVE

This review (Part I of II) focuses on specific ERS and UPR signalling regulators, their expression in the cancer phenotype and apoptosis, and proposes how their implication in these processes can be rationalised into proteasome inhibition, apoptosis induction and the development of more efficacious targeted molecular cancer therapies.

METHOD

In this review, we contextualise many ERS and UPR client proteins that are deregulated or mutated in cancers and show links between ERS and the UPR, their implication in oncogenic transformation, tumour progression and escape from immune surveillance, apoptosis inhibition, angiogenesis, metastasis, acquired drug resistance and poor cancer prognosis.

CONCLUSION

Evasion of programmed cell death or apoptosis is a hallmark of cancer that enables tumour cells to proliferate uncontrollably. Successful eradication of cancer cells through targeting ERS- and UPR-associated proteins to induce apoptosis is currently being pursued as a central tenet of anticancer drug discovery.

The p53 tumor suppressor network in cancer and the therapeutic modulation of cell death

The molecular subversion of cell death is acknowledged as a principal contributor to the development and progression of cancer. The p53 tumor suppressor protein is among the most commonly altered proteins in human cancer. The p53 protein mediates critical functions within cells including the response to genotoxic stress, differentiation, senescence, and cell death. Loss of p53 function can result in enhanced rates of cell proliferation, resistance to cell death stimuli, genomic instability, and metastasis. The community of cancer scientists is now in possession of a vast repository of information regarding the frequency, specific mechanisms, and clinical context of cell death deregulation in cancer. This information has enabled the design of therapeutic agents to target proteins, including p53. The feasibility and impact of targeting cell death signaling proteins has been established in preclinical models of human cancer. The appropriate application of these targeted agents is now being established in clinical trials.

Effect of ursolic acid, a triterpenoid antioxidant, on ultraviolet-B radiation-induced cytotoxicity, lipid peroxidation and DNA damage in human lymphocytes

Exposure to ultraviolet B (UVB, 280-320) radiation induces the formation of reactive oxygen species (ROS) in the biological system. In this study, we examined the protective effect of ursolic acid on UVB-induced lipid peroxidation and oxidative DNA damage with reference to alterations in cellular antioxidant status in human lymphocytes. Series of in vitro tests (hydroxyl radical, superoxide, nitric oxide, DPPH and ABTS radical scavenging assays) demonstrates antioxidant property of ursolic acid in our study. Treatment of lymphocytes with ursolic acid alone (at 10 microg/mL) gave no significant change in cell viability, thiobarbituric acid reactive substances (TBARSs), lipid hydroperoxides (LHPs), % tail DNA and tail moment when compared with normal lymphocytes. UVB-exposure significantly increased TBARS, LHP and % tail DNA, tail moment; decreased % cell viability and antioxidant status in irradiated lymphocytes. Treatment with ursolic acid 30 min prior to UVB-exposure resulted in a significant decline of TBARS, LHP, % tail DNA and tail moment and increased % cell viability as ursolic acid concentration increased. Based on our results we conclude that ursolic acid, a dietary antioxidant, mediates its protective effect through modulation of UVB-induced reactive oxygen species.

Increased damage of exon 5 of p53 gene in workers from an arsenic plant

Mutagenesis is a multistage process. Substitution mutations can be induced by base modified through alteration of pairing property. Mutations of exon 5 and 8 of p53 gene have been found in most arsenicosis patients with precarcinomas and carcinomas, but never in arsenicosis individuals without precarcinomas and carcinomas. This study investigates whether base modification exists in exon 5 and 8 of p53 gene, and explores the dose-effect relationship between damage of exon 5 of p53 gene and urinary arsenic. Concentrations of urinary 8-hydroxydeoxyguanine (8-OHdG) are analyzed to identify the occurrence of DNA damage. The real-time PCR developed by Sikorsky et al. is applied to detect base modification in exon 5 and 8 of p53 gene for apparently healthy participants. Our results show that the mean total arsenic concentrations of two exposed groups from an arsenic plant are significantly elevated compared with the control group, and the damage level of exon 5 of the high-exposed group is significantly higher than that of the control group, but which does not happen in exon 8. The closely correlation between the damage index of exon 5 and urinary organic arsenic concentration are found. Concentration of 8-OHdG of the high-exposed group is significantly higher than that of the control group. These results imply that base modification in exon 5 of p53 gene can be induced by arsenic. In addition, our study suggests that the damage level of exon 5 is a useful biomarker to assess adverse health effect levels caused by chronic exposure to arsenic.

Photoexposition discriminates Notch 1 expression in human cutaneous squamous cell carcinoma

The Notch signaling pathway may play opposing roles in cancer. It can be oncosuppressive or protumoral, depending on the cellular and tissue context. In skin cancer, Notch 1 expression is downregulated, thus supporting the hypothesis of an oncosuppressive role in cutaneous carcinomas. However, as members of the Notch family undergo downregulation upon exposure to UV irradiation, we wondered whether Notch 1 expression in skin carcinomas may be governed by additional factors, including UV exposure. We investigated the expression of Notch 1 and its ligands, Jagged 1, Jagged 2 and Delta-like 1, by immunohistochemistry in a series of premalignant and invasive cutaneous carcinomas, including 4 solar keratoses, 5 Bowen's disease, 5 squamous cell carcinomas on sun-exposed skin, 6 squamous cell carcinomas on sun-protected genital skin and 14 basal cell carcinomas of different histotypes (nodular, superficial type, sclerodermiform/infiltrating and baso-squamous). Expression of Notch 1 was decreased in solar keratoses and invasive squamous cell carcinomas localized on sun-exposed skin. In contrast, marked Notch 1 staining was observed in extragenital Bowen's disease as well as in genital (penile) human papilloma virus-related in situ and invasive squamous cell carcinomas. A diffuse Notch 1 staining was detected in nodular and superficial basal cell carcinomas while sclerodermiform/infiltrating and baso-squamous basal cell carcinomas showed a low to absent Notch 1 expression. Jagged 1, Jagged 2 and Delta-like 1 proteins were expressed in all tissues examined. Present findings show divergent expression of Notch 1 in skin cancer, depending on anatomical site and tumor histotype. Thus, whereas in UV-related squamous cell photocarcinogenesis Notch 1 downregulation could mirror a tumor suppressor function of the receptor, in sun-protected squamous cell carcinomas Notch 1 was upregulated. Furthermore, Notch 1 expression was minimal in basal cell carcinoma subtypes correlated with risk of recurrence (sclerodermiform/infiltrating and baso-squamous) in comparison with nodular and superficial types.