The epigenetic DNA modification 5-carboxylcytosine promotes high levels of cyclobutane pyrimidine dimer formation upon UVB irradiation

Comparison of the mechanisms of DNA damage following photoexcitation and chemiexcitation

In this review, we compare the mechanisms and consequences of electronic excitation of DNA via photon absorption or photosensitization, as well as by chemically induced generation of excited states. The absorption of UV radiation by DNA is known to produce cyclobutane pyrimidine dimers (CPDs) and thymine pyrimidone photoproducts. Photosensitizers are known to enable such transformations using UV-A and visible light by generating triplet species able to transfer energy to DNA. Conversely, chemiexcitation of DNA is a process related to the formation of high energy peroxides whose decomposition leads to triplet excited species. In practice, both photoexcitation and chemiexcitation produce reactive excited species able to promote some DNA nucleobases to their excited state. We discuss the effect of epigenetic methylation modifications of DNA and the role of endogenous and exogenous photosensitizers on the formation of DNA photoproducts via triplet-triplet energy transfer as well as oxidative DNA damages. The mechanisms of pathogenic pathway involving the generation of CPDs via chemiexcitation (namely dark CPDs, dCPDs) are discussed and compared with photoexcitation considering their spatiotemporal characteristics. Recognition of the multifaceted noxious effects of UV radiation opens new horizons for the development of effective electronically excited quenchers, thereby providing a crucial step toward mitigating DNA photodamage.

Ultraviolet (UV) radiation: a double-edged sword in cancer development and therapy

It has long been widely acknowledged that ultraviolet (UV) light is an environment risk factor that can lead to cancer, particularly skin cancer. However, it is worth noting that UV radiation holds potential for cancer treatment as a relatively high-energy electromagnetic wave. With the help of nanomaterials, the role of UV radiation has caught increasing attention in cancer treatment. In this review, we briefly summarized types of UV-induced cancers, including malignant melanoma, squamous cell carcinoma, basal cell carcinoma, Merkel cell carcinoma. Importantly, we discussed the primary mechanisms underlying UV carcinogenesis, including mutations by DNA damage, immunosuppression, inflammation and epigenetic alterations. Historically limited by its shallow penetration depth, the introduction of nanomaterials has dramatically transformed the utilization of UV light in cancer treatment. The direct effect of UV light itself generally leads to the suppression of cancer cell growth and the initiation of apoptosis and ferroptosis. It can also be utilized to activate photosensitizers for reactive oxygen species (ROS) production, sensitize radiotherapy and achieve controlled drug release. Finally, we comprehensively weigh the significant risks and limitations associated with the therapeutic use of UV radiation. And the contradictory effect of UV exposure in promoting and inhibiting tumor has been discussed. This review provides clues for potential clinical therapy as well as future study directions in the UV radiation field. The precise delivery and control of UV light or nanomaterials and the wavelength as well as dose effects of UV light are needed for a thorough understanding of UV radiation.

Ultrafast Formation of a Delocalized Triplet-Excited State in an Epigenetically Modified DNA Duplex under Direct UV Excitation

Epigenetic modifications impart important functionality to nucleic acids during gene expression but may increase the risk of photoinduced gene mutations. Thus, it is crucial to understand how these modifications affect the photostability of duplex DNA. In this work, the ultrafast formation (<20 ps) of a delocalized triplet charge transfer (CT) state spreading over two stacked neighboring nucleobases after direct UV excitation is demonstrated in a DNA duplex, d(G5fC)9•d(G5fC)9, made of alternating guanine (G) and 5-formylcytosine (5fC) nucleobases. The triplet yield is estimated to be 8 ± 3%, and the lifetime of the triplet CT state is 256 ± 22 ns, indicating that epigenetic modifications dramatically alter the excited state dynamics of duplex DNA and may enhance triplet state-induced photochemistry.

Endogenous Photosensitizers in Human Skin

Endogenous photosensitizers play a critical role in both beneficial and harmful light-induced transformations in biological systems. Understanding their mode of action is essential for advancing fields such as photomedicine, photoredox catalysis, environmental science, and the development of sun care products. This review offers a comprehensive analysis of endogenous photosensitizers in human skin, investigating the connections between their electronic excitation and the subsequent activation or damage of organic biomolecules. We gather the physicochemical and photochemical properties of key endogenous photosensitizers and examine the relationships between their chemical reactivity, location within the skin, and the primary biochemical events following solar radiation exposure, along with their influence on skin physiology and pathology. An important take-home message of this review is that photosensitization allows visible light and UV-A radiation to have large effects on skin. The analysis presented here unveils potential causes for the continuous increase in global skin cancer cases and emphasizes the limitations of current sun protection approaches.

Post-Translational Modifications by Lipid Metabolites during the DNA Damage Response and Their Role in Cancer

Genomic DNA damage occurs as an inevitable consequence of exposure to harmful exogenous and endogenous agents. Therefore, the effective sensing and repair of DNA damage are essential for maintaining genomic stability and cellular homeostasis. Inappropriate responses to DNA damage can lead to genomic instability and, ultimately, cancer. Protein post-translational modifications (PTMs) are a key regulator of the DNA damage response (DDR), and recent progress in mass spectrometry analysis methods has revealed that a wide range of metabolites can serve as donors for PTMs. In this review, we will summarize how the DDR is regulated by lipid metabolite-associated PTMs, including acetylation, S-succinylation, N-myristoylation, palmitoylation, and crotonylation, and the implications for tumorigenesis. We will also discuss potential novel targets for anti-cancer drug development.

The ups and downs of DNA methylation: an interview with Gerd Pfeifer

In this interview, Professor Gerd Pfeifer speaks with Storm Johnson, Commissioning Editor for Epigenomics, on his work to date in the field of DNA methylation. Dr Pfeifer received a PhD degree from the University of Frankfurt, Germany. After postdoctoral work, he became a faculty member at the Beckman Research Institute of the City of Hope (Duarte, CA) in 1991. He is currently a full professor at the Van Andel Institute in Grand Rapids, MI. Dr. Pfeifer has served on several NIH advisory committees and has published over 300 research papers. Dr Pfeifer's research interests are cancer etiology, molecular carcinogenesis and epigenetics. His expertise is in cellular and molecular biology. His lab currently works on epigenetic mechanisms of gene regulation in cancer and other diseases.

The Impact of Hyaluronan on Tumor Progression in Cutaneous Melanoma

The incidence of cutaneous melanoma is rapidly increasing worldwide. Cutaneous melanoma is an aggressive type of skin cancer, which originates from malignant transformation of pigment producing melanocytes. The main risk factor for melanoma is ultraviolet (UV) radiation, and thus it often arises from highly sun-exposed skin areas and is characterized by a high mutational burden. In addition to melanoma-associated mutations such as BRAF, NRAS, PTEN and cell cycle regulators, the expansion of melanoma is affected by the extracellular matrix surrounding the tumor together with immune cells. In the early phases of the disease, hyaluronan is the major matrix component in cutaneous melanoma microenvironment. It is a high-molecular weight polysaccharide involved in several physiological and pathological processes. Hyaluronan is involved in the inflammatory reactions associated with UV radiation but its role in melanomagenesis is still unclear. Although abundant hyaluronan surrounds epidermal and dermal cells in normal skin and benign nevi, its content is further elevated in dysplastic lesions and local tumors. At this stage hyaluronan matrix may act as a protective barrier against melanoma progression, or alternatively against immune cell attack. While in advanced melanoma, the content of hyaluronan decreases due to altered synthesis and degradation, and this correlates with poor prognosis. This review focuses on hyaluronan matrix in cutaneous melanoma and how the changes in hyaluronan metabolism affect the progression of melanoma.

Programmed gene expression change in mouse skin after ultraviolet radiation damage

Ultraviolet (UV) radiation is a major cause of skin damage and carcinogenesis. Here, we systematically analyse the acute gene expression change in skin in vivo after UV exposure, aiming to establish the common C57BL/6 mouse strain as a convenient model for future pathological research and drug discovery. The back fur of C57BL/6 mice was depilated, and a mixed UV light source was used to irradiate the skin. Full-thickness skin samples were collected at 0, 0.5, 2, 6, 12 and 24 h. Total RNAs were extracted and subjected to RNA sequencing analysis. We found that the gene expression change in mouse skin is highly similar to previous reports in human skin. These include down-regulation of differentiation-related genes and extracellular matrix genes, and up-regulation of cytokine/chemokine genes. An early wave of activator protein 1 (AP-1) expression is induced, whereas activation of the p53 pathway is not significant. The impact of the AP-1 transcription factors and the antioxidant tea polyphenols is discussed. The analysis of acute gene expression change in skin after UV irradiation provides a starting point to investigate how the skin responds to genotoxic stress.