Background: Multiple studies have compared the performance of artificial intelligence (AI)ebased models for automated skin cancer classification to human experts, thus setting the cornerstone for a successful translation of AI-based tools into clinicopathological practice.

Hyaluronidases are enzymes that degrade hyaluronan, an important component of the extracellular matrix. The mammalian hyaluronidases are considered to be involved in many (patho)physiological processes like fertilization, tumor growth, and metastasis. Bacterial hyaluronidases, also termed hyaluronate lyases, contribute to the spreading of microorganisms in tissues. Such roles for hyaluronidases suggest that inhibitors could be useful pharmacological tools. Potent and selective inhibitors are not known to date, although L-ascorbic acid has been reported to be a weak inhibitor of Streptococcus pneumoniae hyaluronate lyase (SpnHL). The x-ray structure of SpnHL complexed with L-ascorbic acid has been elucidated suggesting that additional hydrophobic interactions might increase inhibitory activity. Here we show that L-ascorbic acid 6-hexadecanoate (Vcpal) is a potent inhibitor of both streptococcal and bovine testicular hyaluronidase (BTH). Vcpal showed strong inhibition of Streptococcus agalactiae hyaluronate lyase with an IC 50 of 4 M and weaker inhibition of SpnHL and BTH with IC 50 values of 100 and 56 M, respectively. To date, Vcpal has proved to be one of the most potent inhibitors of hyaluronidase. We also determined the x-ray structure of the SpnHL-Vcpal complex and confirmed the hypothesis that additional hydrophobic interactions with Phe-343, His-399, and Thr-400 in the active site led to increased inhibition. A homology structural model of BTH was also generated to suggest binding modes of Vcpal to this hyaluronidase. The long alkyl chain seemed to interact with an extended, hydrophobic channel formed by mostly conserved amino acids Ala-84, Leu-91, Tyr-93, Tyr-220, and Leu-344 in BTH.

Post-translational modification of nuclear proteins with poly(ADP-ribose) modulates chromatin structure and may be required for DNA processing events such as replication, repair and transcription. The polymer-catabolizing enzyme, poly(ADP-ribose) glycohydrolase, is crucial for the regulation of polymer metabolism and the reversibility of the protein modification. Previous reports have shown that glycohydrolase digests poly(ADP-ribose) via an exoglycosidic mechanism progressing from the protein-distal end of the polymer. Using two independent approaches, we investigated the possibility that poly(ADP-ribose) glycohydrolase also engages in endoglycosidic cleavage of polymers. First, partial glycohydrolase digestion of protein-bound poly(ADP-ribose) led to the production of protein-free oligomers of ADP-ribose. Second, partial glycohydrolase digestion of a fixed number of protein-free poly(ADP-ribose) polymers resulted in a transient increase in the absolute number of polymers while polymer size continuously decreased. Furthermore, endoglycosidic activity produced linear polymers from branched polymers although branch points themselves were not a preferential target of cleavage. From these data, we propose a mechanism whereby poly(ADPribose) glycohydrolase degrades polymers in three distinct phases ; (a) endoglycosidic cleavage, (b) endoglycosidic cleavage plus exoglycosidic, processive degradation, (c) exoglycosidic, distributive degradation.Poly(ADP-ribose) glycohydrolase is the only nuclear enzyme known to hydrolyze a-( 1"-2') glycosidic linkages. The natural substrate for this enzyme is poly(ADP-ribose), which is formed by the nuclear enzyme poly(ADP-ribose) polymerase and can contain branches. The polymers are covalently bound to various acceptor proteins, all of which bind to nucleic acids. Synthesis and degradation of these polymers is thought to regulate protein-DNA interactions during DNA processes involving single-strand and double-strand breaks (reviewed in [l -31). Polymer catabolism by poly(ADP-ribose) glycohydrolase is stimulated in mammalian cells exposed to increasing doses of DNA-damaging agents [4] and is reduced in a murine lymphoma cell line deficient in a specific repair function [5].The molecular mechanism by which poly(ADP-ribose) glycohydrolase degrades polymers has been investigated by several groups in the past. Most of these studies indicated that the glycohydrolase hydrolyzes ribose-ribose linkages from the protein-distal end of the polymer, i.e. exoglycosidically [6-lo]. The results from Ikejima and Gill, however, suggested the possibility of endoglycosidic attack [ 111. We present an in-depth study in which purified poly(ADP-ribose) glycohydrolase was incubated with protein-bound or protein-free ADP-ribose polymers, and the reaction products were directly analyzed on high-resolution DNA sequencing gels and by high-performance liquid chromatography. The results show that poly(ADP-ribose) glycohydrolase produces endoglycosidic reaction products in that (a) glycohydrolase activity releases...

Ultraviolet B (UVB) radiation induces mutagenic DNA photoproducts, in particular cyclobutane pyrimidine dimers (CPDs), in epidermal keratinocytes (KC). To prevent skin carcinogenesis, these DNA photoproducts must be removed by nucleotide excision repair (NER) or apoptosis. Here we report that the UVB-sensitive transcription factor aryl hydrocarbon receptor (AHR) attenuates the clearance of UVB-induced CPDs in human HaCaT KC and skin from SKH-1 hairless mice. Subsequent RNA interference and inhibitor studies in KC revealed that AHR specifically suppresses global genome but not transcription-coupled NER. In further experiments, we found that the accelerated repair of CPDs in AHR-compromised KC depended on a modulation of the p27 tumor suppressor protein. Accordingly, p27 protein levels were increased in AHR-silenced KC and skin biopsies from AHR−/− mice, and critical for the improvement of NER. Besides increasing NER activity, AHR inhibition was accompanied by an enhanced occurrence of DNA double-strand breaks triggering KC apoptosis at later time points after irradiation. The UVB-activated AHR thus acts as a negative regulator of both early defense systems against carcinogenesis, NER and apoptosis, implying that it exhibits tumorigenic functions in UVB-exposed skin. In fact, AHR−/− mice developed 50% less UVB-induced cutaneous squamous cell carcinomas in a chronic photocarcinogenesis study than their AHR+/+ littermates. Taken together, our data reveal that AHR influences DNA damage-dependent responses in UVB-irradiated KC and critically contributes to skin photocarcinogenesis in mice.