Circadian control of XPA and excision repair of cisplatin-DNA damage by cryptochrome and HERC2 ubiquitin ligase

Abstract

Cisplatin is one of the most commonly used anticancer drugs. It kills cancer cells by damaging their DNA, and hence cellular DNA repair capacity is an important determinant of its efficacy. Here, we investigated the repair of cisplatin-induced DNA damage in mouse liver and testis tissue extracts prepared at regular intervals over the course of a day. We find that the XPA protein, which plays an essential role in repair of cisplatin damage by nucleotide excision repair, exhibits circadian oscillation in the liver but not in testis. Consequently, removal of cisplatin adducts in liver extracts, but not in testis extracts, exhibits a circadian pattern with zenith at ∼5 pm and nadir at ∼5 am. Furthermore, we find that the circadian oscillation of XPA is achieved both by regulation of transcription by the core circadian clock proteins including cryptochrome and by regulation at the posttranslational level by the HERC2 ubiquitin ligase. These findings may be used as a guide for timing of cisplatin chemotherapy.C hronochemotherapy is the administration of chemotherapeutic drugs at specific times of the day so as to optimize efficacy and minimize side effects of the drug (1, 2). Cisplatin is one of the three most commonly used chemotherapeutic drugs (3) for which chronotherapy is thought to have some beneficial effects. Factors that modulate the efficacy of cisplatin therapy include drug uptake and efflux, DNA adduct formation, DNA repair, and cellular proliferation (4, 5). Cisplatin produces DNA intra-and interstrand diadducts and DNA-protein crosslinks (4), and it is well established that the intrastrand diadducts Pt-(GpG), Pt-(ApG), and Pt-(GpXpG), that constitute up to 90% of the total DNA lesions, are the main cause of its cytotoxicity and hence its therapeutic effects. These lesions are removed exclusively by nucleotide excision repair (excision repair) in mammalian cells and hence the status of excision repair is an important factor in the success of chemotheraphy with cisplatin (4, 6).In humans and mice, excision repair is carried out by the coordinated action of six core repair factors, RPA, XPA, XPC, TFIIH, XPG, and XPF-ERCC1, which remove the damage in the form of 24-32 nt-long oligomers; the resulting gap is filled by DNA polymerases and ligated (7-9).Recently, we found that the rate of excision repair of a UV photoproduct in the mouse brain exhibits a daily rhythm (10). Furthermore, it appears that this rhythmic pattern is due to the circadian (circa ¼ about, dies ¼ day) oscillation of the XPA (xeroderma pigmentosum A) protein that is one of the ratelimiting factors in excision repair. Even though in that study the damaged-DNA substrate was a UV photoproduct, we suggested that the findings were relevant to the repair of cisplatin because nucleotide excision repair is the only repair system capable of removing bulky DNA lesions produced by UV or by UVmimetic agents such as cisplatin (11). Although cisplatin is used for treating certain brain cancers, the blood-brain barrier is a serious impediment for its gen...

Control of skin cancer by the circadian rhythm

“…Previously, we reported that the transcription of the xpa gene and the level of XPA protein exhibited circadian rhythmicity in some mouse tissues such as the brain and the liver but not in others such as testis (11,12). This rhythmicity or the lack thereof (in clock mutant mice) was associated with an oscillatory or a constant rate of repair activity as a function of time of day, respectively.…”

“…The dual incision is carried out by six excision repair factors: RPA, xeroderma pigmentosum group A (XPA), XPC, TFIIH, XPG, and XPF-ERCC1 (10). Recently, in a study that analyzed liver and brain tissues from mice, it was found that XPA, a critical protein involved in damage recognition and a rate-limiting factor in excision repair, is controlled by the core molecular circadian clock (11,12). As a consequence, excision repair activity exhibited circadian rhythmicity in these organs, increasing during the day to reach a maximum at 4-6:00 PM and decreasing during the night to a minimum at 4-6:00 AM.…”

Does evening sun increase the risk of skin cancer?

“…CRY 1and 2 proteins have short half-lives, which is necessary for reactivating the next cycle of transcription, and are degraded via polyubiquitylation (12,13). XPA also has a short life as expected, and is degraded via polyubiquitylation mediated by HERC2 ubiquitin ligase (14).…”

Electric light, particularly at night, disrupts human circadian rhythmicity: is that a problem?

“…As transcriptional regulators, circadian genes mediate the expression of many cancer-related genes and play various roles in cancer-relevant pathways such as DNA repair [84,85]. As such, the epigenetic impact of shift work on the activity and function of core circadian regulators may provide a missing link in the relationship between breast cancer and night shift work.…”