Ultraviolet-B-light-induced mutagenesis of C-H-ras codons 11 and 12 in human skin fibroblasts

Resveratrol-mediated downregulation of Rictor attenuates autophagic process and suppresses UV-induced skin carcinogenesis

Macroautophagy is a cellular response to various environmental stresses that ensures lysosomal degradation of long-lived and damaged proteins and cellular organelles. It occurs through the formation of an autophagosome, which then fuses with a lysosome to form an autolysosome. Depending on the cellular context, autophagy may promote cancer cell survival or it may serve as a mechanism of tumor suppression. Herein, we show that resveratrol, a natural phytoalexin, induces premature senescence in human A431 SCC cells, and that resveratrol-induced premature senescence is associated with a blockade of autolysosome formation, as assessed by the absence of colocalization of LC3 and Lamp-2, markers for autophagosomes and lysosomes, respectively. Further, we show that resveratrol downregulates the level of Rictor, a component of mTORC2, leading to decreased RhoA-GTPase and altered actin cytoskeleton organization. Exogenous overexpression of Rictor restores RhoA-GTPase activity and actin cytoskeleton network, and decreases resveratrol-induced senescence-associated β-gal activity, indicating a direct role of Rictor in senescence induction. Rictor is overexpressed in UV-induced murine SCCs, whereas its expression is diminished by oral administration of resveratrol. These data indicate that resveratrol attenuates autophagic process via Rictor, and suggest that downregulation of Rictor may be a mechanism of tumor suppression associated with premature senescence.

Effects of macelignan isolated from Myristica fragrans Houtt. on UVB-induced matrix metalloproteinase-9 and cyclooxygenase-2 in HaCaT cells

BACKGROUND

UVB irradiation (290-320 nm) is the most damaging component of the UV spectrum and causes both direct and indirect damage to the basal cell layer of the epidermis; this results in the activation of a number of signaling pathways involved in pathophysiological processes in the skin, such as photoaging and inflammation. In photoaging UVB irradiation promotes degradation of the extracellular matrix (ECM) by matrix metalloproteinases (MMPs) and, in inflammation, UVB irradiation promotes the expression of inducible cyclooxygenase (COX-2), leading to overproduction of inflammatory mediators.

OBJECTIVE

We first investigated the protective effects of macelignan from Myristica fragrans Houtt. on immortalized human keratinocytes (HaCaT) against UVB damage. We then explored the inhibitory effects of macelignan on UVB-induced MMP-9 and COX-2 and investigated the molecular mechanism underlying those effects.

METHODS

HaCaT cells were treated with macelignan for the indicated times followed by irradiation with UVB. Secretion of MMP-9 was measured by gelatin zymography. Expression of COX-2, mitogen-activated protein kinases (MAPKs), phosphatidylinositol 3-kinase/Akt (PI3K/Akt), c-Fos, c-Jun, and CREB were assayed by western analysis.

RESULTS

Macelignan at a concentration of 0.1-1 microM increased the viability of HaCaT cells following UVB irradiation and inhibited MMP-9 secretion and COX-2 expression in a concentration-dependent manner. An inhibitory effect was also seen in the signal transduction network, where macelignan treatment reduced the activation of UVB-induced MAPKs, PI3K/Akt, and their downstream transcription factors.

CONCLUSION

These results suggest that macelignan protects skin keratinocytes from UVB-induced damage and inhibits MMP-9 and COX-2 expression by attenuating the activation of MAPKs and PI3K/Akt.

Viral DNA detection and RAS mutations in actinic keratosis and nonmelanoma skin cancers

BACKGROUND

Actinic keratosis (AK) is a well-established precancerous skin lesion that has the potential to progress to squamous cell carcinoma (SCC). Basal cell carcinoma (BCC) is a locally aggressive slowly growing tumour that rarely metastasizes. A number of viruses have been proposed to play a role in the development of nonmelanoma skin cancers (NMSC), but the most plausible evidence to date suggests that cutaneous human papillomavirus (HPV) is the key instigating factor.

OBJECTIVES

To evaluate the prevalence of HPV, cytomegalovirus (CMV), herpes simplex virus (HSV) and Epstein-Barr virus (EBV) and investigate their relationship with the presence of RAS gene mutations in cutaneous lesions obtained from nonimmunosuppressed patients.

METHODS

HPV, CMV, HSV and EBV detection was performed using polymerase chain reaction (PCR) in skin biopsies (26 AK, 12 SCC and 15 BCC samples) that were collected from immunocompetent patients. The RAS mutation incidence was also investigated in all cutaneous lesions by use of PCR/restriction fragment length polymorphism and direct DNA sequencing.

RESULTS

Seventeen out of 53 (32%) skin lesions were found to be positive for HPV DNA. The highest incidences of HPV infection were five of 15 (33%) in BCC and four of 12 (33%) in SCC specimens. The HPV incidence was eight of 26 (31%) in AK and eight of 53 (15%) in normal skin tissue. Twelve out of 53 (23%) skin lesions were CMV-positive. The highest incidence of CMV infection was six of 15 (40%), observed in BCC specimens. The CMV incidence was two of 26 (8%) in AK and four of 12 (33%) in SCC. No normal skin biopsy was found to be positive for CMV. All cutaneous samples were negative for HSV and EBV DNA, as assessed by our PCR-based assays. Only three samples, one AK (4%), one BCC (6%) and one SCC (8%), were found to carry a G>T transversion at the second position of HRAS codon 12. Both HRAS mutant SCC and BCC biopsies were HPV- and CMV-positive, as well.

CONCLUSIONS

HPV DNA is detected in NMSC, AK and normal skin biopsies. Our results also indicate that CMV is involved in NMSC at higher levels than in premalignant lesions, whereas the virus was not detected in normal skin biopsies. HSV and EBV do not appear to be involved in the pathogenesis of cutaneous lesions. Moreover, we suggest that the HRAS codon 12 mutation is not a very common event in AK or NMSC. Finally, both viral infection and HRAS activation appear to represent independent factors in the aetiology of NMSC, samples of which were obtained from immunocompetent patients.

Immunochemical quantitation of UV-induced oxidative and dimeric DNA damage to human keratinocytes

There is growing evidence to suggest that solar radiation-induced, oxidative DNA damage may play an important role in skin carcinogenesis. Numerous methods have been developed to sensitively quantitate 8-oxo-2'deoxyguanosine (8-oxodG), a recognised biomarker of oxidative DNA damage. Immunoassays may represent a means by which the limitations of many techniques, principally derived from DNA extraction and sample workup, may be overcome. We report the evaluation of probes to thymine dimers and oxidative damage in UV-irradiated cells and the DNA derived therefrom. Thymine dimers were most readily recognised, irrespective of whether in situ in cells or in extracted DNA. However, using antibody-based detection the more subtle oxidative modifications required extraction and, in the case of 8-oxodG, denaturation of the DNA prior to successful recognition. In contrast, a recently described novel probe for 8-oxodG detection showed strong recognition in cells, although appearing unsuitable for use with extracted DNA. The probes were subsequently applied to examine the relative induction of lesions in cells following UV irradiation. Guanine-glyoxal lesions predominated over thymine dimers subsequent to UVB irradiation, whereas whilst oxidative lesions increased significantly following UVA irradiation, no induction of thymine dimers was seen. These data support the emerging importance of oxidative DNA damage in UV-induced carcinogenesis.

Mutational analyses of candidate genes in human squamous cell carcinomas

OBJECTIVES AND STUDY DESIGN

Squamous cell carcinomas are common malignancies and a major cause of mortality. The molecular mechanisms involved in tumorigenesis remain largely unknown, but sequence alterations have been identified in coding regions of several genes. Primary squamous cell carcinomas of various tissues (skin, head and neck, esophagus, lung, penis, uterus, and vagina) from 52 patients were analyzed for the presence of mutations within several candidate genes presumably involved in tumorigenesis: Gsalpha, Gi2alpha, GTPase activating protein (GAP), and patched (PTCH) genes.

METHODS

Mutational analysis scheme included polymerase chain reaction (PCR), denaturing gradient gel electrophoresis (DGGE), single stranded conformational polymorphism (SSCP), and selected sequence analysis.

RESULTS AND CONCLUSION

No tumor had any evidence of mutations in any of these analyzed genes. Mutations within these genes do not occur frequently in an unselected population of patients with squamous cell carcinomas.

Genotypic selection methods for the direct analysis of point mutations

Genotypic selection enriches a particular DNA sequence relative to another closely-related DNA sequence based only on a change of one or a few bases. This review is a survey of the genotypic selection methods that have the sensitivity to detect rare point mutations. These methods are primarily being used to study mutations caused by environmental mutagens; however, the ability to detect and measure very minor DNA sequence populations is likely to further research efforts in many fields. The approaches for allele-selection have intrinsic strengths and weaknesses, and vary greatly in sensitivity. The most sensitive method is Restriction Fragment Length Polymorphism/Polymerase Chain Reaction (RFLP/PCR) by which mutant fractions as low as 1 mutant allele in 10(8) wild-type alleles can be detected. The RFLP/PCR approach is presented as a prototype genotypic selection method. Genotypic selection methods are categorized in terms of those that (1) selectively destroy the abundant or wild-type allele, (2) selectively amplify the rare or mutant allele, or (3) spatially separate the alleles. Issues relevant to the further development of genotypic selection methods include initial DNA pool size, strategies to eliminate the bulk of extraneous DNA, the use of an internal copy number standard in quantitative PCR, the fidelity of thermostable DNA polymerases, and the effective use of PCR in linking two or more genotypic selection techniques. We conclude that proficient genotypic selection requires more than one allele-enrichment technique with at least one of these preceding a high-fidelity PCR amplification step.