Effect of Topical Sunscreens on the UV-Radiation–Induced Suppression of the Alloactivating Capacity in Human Skin In Vivo

Levels of the tumor suppressor protein p53 are normally quite low due in part to its short half-life. p53 levels increase in cells exposed to DNA-damaging agents, such as radiation, and this increase is thought to be responsible for the radiation-induced G1 cell cycle arrest or delay. The mechanisms by which radiation causes an increase in p53 are currently unknown. The purpose of this study was to compare the effects of gamma and UV radiation on the stability and ubiquitination of p53 in vivo. Ubiquitin-p53 conjugates could be detected in nonirradiated and gamma-irradiated cells but not in cells which were UV treated, despite the fact that both treatments resulted in the stabilization of the p53 protein. These results demonstrate that UV and gamma radiation have different effects on ubiquitinated p53 and suggest that the UV-induced stabilization of p53 results from a loss of p53 ubiquitination. Ubiquitinated forms of p21, an inhibitor of cyclin-dependent kinases, were detected in vivo, demonstrating that p21 is also a target for degradation by the ubiquitin-dependent proteolytic pathway. However, UV and gamma radiation had no effect on the stability or in vivo ubiquitination of p21, indicating that the radiation effects on p53 are specific.

Download Full-text

Pheomelanin Effect on UVB Radiation-Induced Oxidation/Nitration of L-Tyrosine

International Journal of Molecular Sciences ◽

10.3390/ijms23010267 ◽

2021 ◽

Vol 23 (1) ◽

pp. 267

Author(s):

Alessia Mariano ◽

Irene Bigioni ◽

Anna Scotto d’Abusco ◽

Alessia Baseggio Conrado ◽

Simonetta Maina ◽

...

Keyword(s):

Uv Radiation ◽

Photochemical Reactions ◽

Uvb Radiation ◽

Natural Pigment ◽

Experimental Conditions ◽

Tyrosine Oxidation ◽

Radiation Induced ◽

Cellular Components ◽

Catalyzed Oxidation

Pheomelanin is a natural yellow-reddish sulfur-containing pigment derived from tyrosinase-catalyzed oxidation of tyrosine in presence of cysteine. Generally, the formation of melanin pigments is a protective response against the damaging effects of UV radiation in skin. However, pheomelanin, like other photosensitizing substances, can trigger, following exposure to UV radiation, photochemical reactions capable of modifying and damaging cellular components. The photoproperties of this natural pigment have been studied by analyzing pheomelanin effect on oxidation/nitration of tyrosine induced by UVB radiation at different pH values and in presence of iron ions. Photoproperties of pheomelanin can be modulated by various experimental conditions, ranging from the photoprotection to the triggering of potentially damaging photochemical reactions. The study of the photomodification of l-Tyrosine in the presence of the natural pigment pheomelanin has a special relevance, since this tyrosine oxidation/nitration pathway can potentially occur in vivo in tissues exposed to sunlight and play a role in the mechanisms of tissue damage induced by UV radiation.

Download Full-text