Calcineurin/NFATc1 pathway represses cellular cytotoxicity by modulating histone H3 expression.

Excess amounts of histones in the cell induce mitotic chromosome loss and genomic instability, and are therefore detrimental to cell survival. In yeast, excess histones are degraded by the proteasome mediated via the DNA damage response factor Rad53. Histone expression, therefore, is tightly regulated at the protein level. Our understanding of the transcriptional regulation of histone genes is far from complete. In this study, we found that calcineurin inhibitor treatment increased histone protein levels, and that the transcription factor NFATc1 (nuclear factor of activated T cells 1) repressed histone transcription and acts downstream of the calcineurin. We further revealed that NFATc1 binds to the promoter regions of many histone genes and that histone transcription is downregulated in a manner dependent on intracellular calcium levels. Indeed, overexpression of histone H3 markedly inhibited cell proliferation. Taken together, these findings suggest that NFATc1 prevents the detrimental effects of histone H3 accumulation by inhibiting expression of histone at the transcriptional level.

NFAT activation by FKBP52 promotes cancer cell proliferation by suppressing p53.

FK506-binding protein 52 (FKBP52) is a member of the FKBP family of proline isomerases. FKBP52 is up-regulated in various cancers and functions as a positive regulator of steroid hormone receptors. Depletion of FKBP52 is known to inhibit cell proliferation; however, the detailed mechanism remains poorly understood. In this study, we found that FKBP52 depletion decreased MDM2 transcription, leading to stabilization of p53, and suppressed cell proliferation. We identified NFATc1 and NFATc3 as transcription factors that regulate MDM2 We also found that FKBP52 associated with NFATc3 and facilitated its nuclear translocation. In addition, calcineurin, a well-known Ca2+ phosphatase essential for activation of NFAT, plays a role in MDM2 transcription. Supporting this notion, MDM2 expression was found to be regulated by intracellular Ca2+ Taken together, these findings reveal a new role of FKBP52 in promoting cell proliferation via the NFAT-MDM2-p53 axis, and indicate that inhibition of FKBP52 could be a new therapeutic tool to activate p53 and inhibit cell proliferation.

FOXO1 promotes cancer cell growth through MDM2-mediated p53 degradation.

FOXO1 is a transcription factor and potential tumor suppressor that is negatively regulated downstream of PI3K-PKB/AKT signaling. Paradoxically, FOXO also promotes tumor growth, but the detailed mechanisms behind this role of FOXO are not fully understood. In this study, we revealed a molecular cascade by which the Thr24 residue of FOXO1 is phosphorylated by AKT and is dephosphorylated by calcineurin, which is a Ca2+-dependent protein phosphatase. Curiously, single nucleotide somatic mutations of FOXO1 in cancer occur frequently at and near Thr24. Using a calcineurin inhibitor and shRNA directed against calcineurin, we revealed that calcineurin-mediated dephosphorylation of Thr24 regulates FOXO1 protein stability. We also found that FOXO1 binds to the promoter region of MDM2 and activates transcription, which in turn promotes MDM2-mediated ubiquitination and degradation of p53. FOXO3a and FOXO4 are shown to control p53 activity; however, the significance of FOXO1 in p53 regulation remains largely unknown. Supporting this notion, FOXO1 depletion increased p53 and p21 protein levels in association with the inhibition of cell proliferation. Taken together, these results indicate that FOXO1 is stabilized by calcineurin-mediated dephosphorylation and that FOXO1 supports cancer cell proliferation by promoting MDM2 transcription and subsequent p53 degradation.

Dephosphorylation of NFAT by Calcineurin inhibits Skp2-mediated degradation.

The transcription factor NFAT plays key roles in multiple biological activities, such as immune responses, tissue development and malignant transformation. NFAT is dephosphorylated by calcineurin, which is activated by intracellular calcium levels, and translocated into the nucleus, resulting in transcriptional activation. Calcineurin dephosphorylates various target proteins and regulates their functions. However, the regulation of NFAT degradation is largely unknown, and it is unclear whether calcineurin contributes to the stability of NFAT. We investigated the effect of calcineurin inhibition on NFAT protein stability and found that the dephosphorylation of NFAT by calcineurin promotes the NFAT stabilization, whereas calcineurin mutant that is defective in phosphatase activity was unable to stabilize NFAT. Increased intracellular calcium ion concentration, which is essential for calcineurin activation, also induced NFAT stability. In addition, we identified S-phase kinase associated protein 2 (Skp2), an F-box protein of the SCF ubiquitin ligase complex, as a factor mediating degradation of NFAT when calcineurin was depleted. In summary, these findings revealed that the dephosphorylation of NFAT by calcineurin protects NFAT from degradation by Skp2 and promotes its protein stability.

Phase II study of IRInotecan treatment after COmbined chemo-immunotherapy for extensive-stage small cell lung cancer: Protocol of IRICO study.

INTRODUCTION: Combined treatment using anti-programmed death-ligand 1 antibody (anti-PD-L1) and platinum-etoposide is the current standard first-line treatment for patients with extensive-stage (ES) small cell lung cancer (SCLC). However, the best treatment for relapsed ES-SCLC after the first-line treatment remains unclear. There are some approved chemotherapeutic agents that can be used against ES-SCLC, and treatment with irinotecan is well established as both a monotherapy and a combined therapy, in combination with platinum. Therefore, we conduct a phase II study with irinotecan in the second- or later-line setting for patients with ES-SCLC who have been previously treated with combined treatment. METHODS: Our study will enroll total 30 patients who are diagnosed with ES-SCLC and have experienced disease progression after the combined treatment. Patients will receive irinotecan on days 1, 8, and 15, which will be repeated every 4 weeks. Doses of irinotecan (100/80/60 mg/m2 ) will be determined according to the type of UGT1A1 gene polymorphism, and the treatment will be discontinued following disease progression, intolerance, withdrawal of patient consent, and based on the investigator's decision. The primary endpoint of the study is the response rate, and the secondary endpoints are overall survival, progression-free survival, and safety. DISCUSSION: Since the present first-line treatment has been changed to the combined treatment, the second- or later-line treatment should be re-evaluated for patients with relapsed SCLC. Irinotecan is a major chemotherapeutic agent used for SCLC. This study demonstrates and re-evaluates the clinical benefits of irinotecan after combined treatment with anti-PD-L1 and platinum-etoposide for patients with ES-SCLC. REGISTRATION DETAILS: This study was registered in the Japan Registry of Clinical Trials (no. jRCT s071210090) on November 4, 2021.

Calcineurin-mediated dephosphorylation enhances the stability and transactivation of c-Myc.

c-Myc, a transcription factor, induces cell proliferation and is often aberrantly or highly expressed in cancers. However, molecular mechanisms underlying this aberrantly high expression remain unclear. Here, we found that intracellular Ca2+ concentration regulates c-Myc oncoprotein stability. We identified that calcineurin, a Ca2+-dependent protein phosphatase, is a positive regulator of c-Myc expression. Calcineurin depletion suppresses c-Myc targeted gene expression and c-Myc degradation. Calcineurin directly dephosphorylates Thr58 and Ser62 in c-Myc, which inhibit binding to the ubiquitin ligase Fbxw7. Mutations within the autoinhibitory domain of calcineurin, most frequently observed in cancer, may increase phosphatase activity, increasing c-Myc transcriptional activity in turn. Notably, calcineurin inhibition with FK506 decreased c-Myc expression with enhanced Thr58 and Ser62 phosphorylation in a mouse xenograft model. Thus, calcineurin can stabilize c-Myc, promoting tumor progression. Therefore, we propose that Ca2+ signaling dysfunction affects cancer-cell proliferation via increased c-Myc stability and that calcineurin inhibition could be a new therapeutic target of c-Myc-overexpressing cancers.

Genetic profile of thymic epithelial tumors in the Japanese population: an exploratory study examining potential therapeutic targets.

Background: Thymic epithelial tumors (TETs) are prone to developing in East Asian populations. However, little is known about the genomic profile of TETs in East Asian populations, and the genomic aberrations in TETs have not yet been fully clarified. Thus, molecular targeted therapies for patients with TETs have not been established. This prospective study was conducted to explore the genetic abnormalities of surgically resected TETs in a Japanese cohort and to identify clues for carcinogenesis and potential therapeutic targets in TETs. Methods: Genetic profiles of TETs were investigated using fresh-frozen specimens resected from operable cases with TETs. DNA sequencing was performed using a next-generation sequencing (NGS) gene panel test with Ion Reporter™ and CLC Genomics Workbench 11.0. The mutation sites were further confirmed by Sanger sequencing, digital droplet polymerase chain reaction (ddPCR), and TA cloning for validation. Results: Among 43 patients diagnosed with anterior mediastinal tumors between January 2013 and March 2019, NGS and validation analyses were performed in 31 patients [29 thymomas and two thymic cancers (TCs)] who met the study criteria. Of these, 12 cases of thymoma types A, AB, B1, and B2 harbored the general transcription factor 2-I (GTF2I) mutation (L424H). Conversely, the mutation was not detected in type B3 thymoma or TC, suggesting that the GTF2I mutation existed in indolent types of TETs. Rat sarcoma viral oncogene (RAS) mutations were detected in three cases [Harvey RAS (HRAS) in two cases of type AB thymoma and neuroblastoma RAS (NRAS)] in one case of type B1 thymoma), and additional sex combs like 1 (ASXL1) mutation was present in one case of TC. All RAS mutations were observed in GTF2I-mutated cases. Conclusions: The GTF2I mutation (L424H) is the most frequently occurring mutation in the limited histology of thymoma, consistent with those in the non-Asian population. HRAS and NRAS mutations co-occurred in cases harboring the GTF2I mutation. These findings suggest that the existence of the GTF2I mutation might be related to indolent types of TETs, and RAS mutations could be candidates as therapeutic targets in TETs.

Impact of FKBP52 on cell proliferation and hormone-dependent cancers.

FK506 binding protein 52 (FKBP52) (gene name FKBP4) is a 52 kDa protein that belongs to the FKBP family; it binds to the immunosuppressant FK506 and has proline isomerase activity. In addition to its FK domain-containing peptidylprolyl isomerase activity, FKBP52 also acts as a cochaperone through the tetratricopeptide repeat domain that mediates binding to heat shock protein 90. Previous studies have reported that FKBP52 is associated with hormone-dependent, stress-related, and neurodegenerative diseases, revealing its diverse functions. In particular, the effects of FKBP52 on cancer have attracted considerable attention. FKBP52 promotes the growth of hormone-dependent cancers by activating steroid hormone receptors. Recent studies have shown that the expression of FKBP52 is increased not only in steroid hormone-dependent cancer cells but also in colorectal, lung, and liver cancers, revealing its diverse functions that contribute to cancer growth. This review summarizes reports related to hormone-dependent cancer and cell proliferation in terms of the structure of FKBP52 and its function on interacting molecules.

Dephosphorylation of the EGFR protein by calcineurin at serine 1046/1047 enhances its stability.

The epidermal growth factor receptor (EGFR) is highly expressed or abnormally activated in several types of cancers, such as lung and colorectal cancers. Inhibitors that suppress the tyrosine kinase activity of EGFR have been used in the treatment of lung cancer. However, resistance to these inhibitors has become an issue in cancer treatment, and the development of new therapies that inhibit EGFR is desired. We found that calcineurin, a Ca2+/calmodulin-activated serine/threonine phosphatase, is a novel regulator of EGFR. Inhibition of calcineurin by FK506 treatment or calcineurin depletion promoted EGFR degradation in cancer cells. In addition, we found that calcineurin dephosphorylates EGFR at serine (S)1046/1047, which in turn stabilizes EGFR. Furthermore, in human colon cancer cells transplanted into mice, the inhibition of calcineurin by FK506 decreased EGFR expression. These results indicate that calcineurin stabilizes EGFR by dephosphorylating S1046/1047 and promotes tumor growth. These findings suggest that calcineurin may be a new therapeutic target for cancers with high EGFR expression or activation.

Estrogen receptor α revised: Expression, structure, function, and stability.

Estrogen receptor α (ERα) is a ligand-dependent transcription factor that regulates the expression of estrogen-responsive genes. Approximately 70% of patients with breast cancer are ERα positive. Estrogen stimulates cancer cell proliferation and contributes to tumor progression. Endocrine therapies, which suppress the ERα signaling pathway, significantly improve the prognosis of patients with breast cancer. However, the development of de novo or acquired endocrine therapy resistance remains a barrier to breast cancer treatment. Therefore, understanding the regulatory mechanisms of ERα is essential to overcome the resistance to treatment. This review focuses on the regulation of ERα expression, including copy number variation, epigenetic regulation, transcriptional regulation, and stability, as well as functions from the point of view post-translational modifications.

Immunosuppressive tumor microenvironment in extraskeletal myxoid chondrosarcoma: A case of pleural metastases.

Extraskeletal myxoid chondrosarcoma (EMCS) is an undifferentiated mesenchymal malignancy; however, its immune microenvironment remains to be elucidated. The case of a 34-year-old woman who developed EMCS metastasizing to the pleura is presented here. The pleural EMCS showed hypervascularity, absent PD-L1 expression, and a lack of tumor mutational burden and pathogenic variants. Immunohistological examination of the pleural lesions showed predominant M2 macrophages and sparse CD8+ T cells. EMCS and the tumor stroma were positive for transforming growth factor-ß1 (TGF-ß1) and vascular endothelial growth factor (VEGF). In contrast, a small number of the stromal vessels were positive for hypoxia inducible factor-1α (HIF-1α). TGF-ß1 and VEGF in the tumor stroma and low antigenicity of the tumor cells may help explain how EMCS induced the immunosuppressive microenvironment. These findings may encourage investigators to explore novel combined immunotherapy for EMCS, such as TGF-ß1 and VEGF inhibitors, and specific therapy for enhancing tumor antigens.

Phase I study of amrubicin plus cisplatin and concurrent accelerated hyperfractionated thoracic radiotherapy for limited-disease small cell lung cancer: protocol of ACIST study.

BACKGROUND: Etoposide plus cisplatin (EP) combined with concurrent accelerated hyperfractionated thoracic radiotherapy (AHTRT) is the standard treatment strategy for unresectable limited-disease (LD) small cell lung cancer (SCLC), which has remained unchanged for over two decades. Based on a previous study that confirmed the non-inferiority of amrubicin (AMR) plus cisplatin (AP) when compared with EP for extensive-disease (ED) SCLC, we have previously conducted a phase I study assessing AP with concurrent TRT (2 Gy/time, once daily, 50 Gy in total) for LD-SCLC therapy. Our findings revealed that AP with concurrent TRT could prolong overall survival to 39.5 months with manageable toxicities. Therefore, we plan to conduct a phase I study to investigate and determine the effect of AP combined with AHTRT, recommended dose (RD), maximum tolerated dose (MTD), and dose-limiting toxicity (DLT) of AP in patients with LD-SCLC. METHODS: Treatment-naive patients with LD-SCLC, age between 20 and 75 years, who had a performance status of 0 or 1 and adequate organ functions will be enrolled. For chemotherapy, cisplatin 60 mg/m2 /day (day 1) and AMR (day 1 to 3) will be administered with AHTRT (1.5 Gy/time, twice daily, 45 Gy in total). The initial AMR dose is set to 25 mg/m2 /day. RD and MTD will be determined by evaluating toxicities. DISCUSSION: Based on our previous study, the initial dose of AMR 25 mg/m2 is expected to be tolerated and acceptable. Here, we aim to determine whether treatment with AP and concurrent AHTRT would be an optimal choice with manageable toxicities for LD-SCLC.

FKBP52 and FKBP51 differentially regulate the stability of estrogen receptor in breast cancer.

Estrogen receptor α (ERα) is a transcription factor that induces cell proliferation and exhibits increased expression in a large subset of breast cancers. The molecular mechanisms underlying the up-regulation of ERα activity, however, remain poorly understood. We identified FK506-binding protein 52 (FKBP52) as a factor associated with poor prognosis of individuals with ERα-positive breast cancer. We found that FKBP52 interacts with breast cancer susceptibility gene 1 and stabilizes ERα, and is essential for breast cancer cell proliferation. FKBP52 depletion resulted in decreased ERα expression and proliferation in breast cancer cell lines, including MCF7-derived fulvestrant resistance (MFR) cells, suggesting that inhibiting FKBP52 may provide a therapeutic effect for endocrine therapy­resistant breast cancer. In contrast, FKBP51, a closely related molecule to FKBP52, reduced the stability of ERα. Consistent with these findings, FKBP51 was more abundantly expressed in normal tissues than in cancer cells, suggesting that these FKBPs may function in the opposite direction. Collectively, our study shows that FKBP52 and FKBP51 regulate ERα stability in a reciprocal manner and reveals a regulatory mechanism by which the expression of ERα is controlled.

Decoding the Phosphatase Code: Regulation of Cell Proliferation by Calcineurin.

Calcineurin, a calcium-dependent serine/threonine phosphatase, integrates the alterations in intracellular calcium levels into downstream signaling pathways by regulating the phosphorylation states of several targets. Intracellular Ca2+ is essential for normal cellular physiology and cell cycle progression at certain critical stages of the cell cycle. Recently, it was reported that calcineurin is activated in a variety of cancers. Given that abnormalities in calcineurin signaling can lead to malignant growth and cancer, the calcineurin signaling pathway could be a potential target for cancer treatment. For example, NFAT, a typical substrate of calcineurin, activates the genes that promote cell proliferation. Furthermore, cyclin D1 and estrogen receptors are dephosphorylated and stabilized by calcineurin, leading to cell proliferation. In this review, we focus on the cell proliferative functions and regulatory mechanisms of calcineurin and summarize the various substrates of calcineurin. We also describe recent advances regarding dysregulation of the calcineurin activity in cancer cells. We hope that this review will provide new insights into the potential role of calcineurin in cancer development.

FKBP51 and FKBP52 regulate androgen receptor dimerization and proliferation in prostate cancer cells.

The growth of prostate cancer is dependent on the androgen receptor (AR), which serves as a ligand-specific transcription factor. Although two immunophilins, FKBP51 and FKBP52, are known to regulate AR activity, the precise mechanism remains unclear. We found that depletion of either FKBP51 or FKBP52 reduced AR dimer formation, chromatin binding, and phosphorylation, suggesting defective AR signaling. Furthermore, the peptidyl-prolyl cis/trans isomerase activity of FKBP51 was found to be required for AR dimer formation and cancer cell growth. Treatment of prostate cancer cells with FK506, which binds to the FK1 domain of FKBPs, or with MJC13, an inhibitor of FKBP52-AR signaling, also inhibited AR dimer formation. Finally, elevated expression of FKBP52 was associated with a higher rate of prostate-specific antigen recurrence in patients with prostate cancer. Collectively, these results suggest that FKBP51 and FKBP52 might be promising targets for prostate cancer treatment through the inhibition of AR dimer formation.

Onset of pulmonary Epstein-Barr virus-positive diffuse large B-cell lymphoma in a patient with silicosis.

How Epstein-Barr virus (EBV)-positive diffuse large B-cell lymphoma (DLBCL) occasionally occurs following chronic inflammation remains to be elucidated. The case of a 57-year-old man who developed pulmonary EBV-positive DLBCL from underlying silicosis lesions is presented. Immunohistochemical examination of the resected silicosis lesions showed predominant helper T cells and M1/M2 macrophages, with a lack of B cells, regulatory T cells, and resident memory T cells. Two years later, EBV-positive DLBCL emerged unexpectedly from the silicosis. The imbalance of the immune cells in the microenvironment, at least in part, may help explain how chronic inflammation contributes to EBV-positive DLBCL.

Calcineurin regulates the stability and activity of estrogen receptor α.

Estrogen receptor α (ER-α) mediates estrogen-dependent cancer progression and is expressed in most breast cancer cells. However, the molecular mechanisms underlying the regulation of the cellular abundance and activity of ER-α remain unclear. We here show that the protein phosphatase calcineurin regulates both ER-α stability and activity in human breast cancer cells. Calcineurin depletion or inhibition down-regulated the abundance of ER-α by promoting its polyubiquitination and degradation. Calcineurin inhibition also promoted the binding of ER-α to the E3 ubiquitin ligase E6AP, and calcineurin mediated the dephosphorylation of ER-α at Ser294 in vitro. Moreover, the ER-α (S294A) mutant was more stable and activated the expression of ER-α target genes to a greater extent compared with the wild-type protein, whereas the extents of its interaction with E6AP and polyubiquitination were attenuated. These results suggest that the phosphorylation of ER-α at Ser294 promotes its binding to E6AP and consequent degradation. Calcineurin was also found to be required for the phosphorylation of ER-α at Ser118 by mechanistic target of rapamycin complex 1 and the consequent activation of ER-α in response to ß-estradiol treatment. Our study thus indicates that calcineurin controls both the stability and activity of ER-α by regulating its phosphorylation at Ser294 and Ser118 Finally, the expression of the calcineurin A-α gene (PPP3CA) was associated with poor prognosis in ER-α-positive breast cancer patients treated with tamoxifen or other endocrine therapeutic agents. Calcineurin is thus a promising target for the development of therapies for ER-α-positive breast cancer.

Real-World Incidence of Febrile Neutropenia among Patients Treated with Single-Agent Amrubicin: Necessity of the Primary Prophylactic Administration of Granulocyte Colony-Stimulating Factor.

BACKGROUND: Single-agent amrubicin chemotherapy is a key regimen, especially for small cell lung cancer (SCLC); however, it can cause severe myelosuppression. PURPOSE: The purpose of this study was to determine the real-world incidence of febrile neutropenia (FN) among patients treated with single-agent amrubicin chemotherapy for thoracic malignancies. PATIENTS AND METHODS: The medical records of consecutive patients with thoracic malignancies, including SCLC and non-small cell lung cancer (NSCLC), who were treated with single-agent amrubicin chemotherapy in cycle 1 between January 2010 and March 2020, were retrospectively analyzed. RESULTS: One hundred and fifty-six patients from four institutions were enrolled. Their characteristics were as follows: median age (range): 68 (32-86); male/female: 126/30; performance status (0/1/2): 9/108/39; SCLC/NSCLC/others: 111/30/15; and prior treatment (0/1/2/3-): 1/96/31/28. One hundred and thirty-four (86%) and 97 (62%) patients experienced grade 3/4 and grade 4 neutropenia, respectively. One hundred and twelve patients (72%) required therapeutic G-CSF treatment, and 47 (30%) developed FN. Prophylactic PEG-G-CSF was not used in cycle 1 in any case. The median overall survival of the patients with FN was significantly shorter than that of the patients without FN (7.2 vs. 10.0 months, p = 0.025). CONCLUSIONS: The real-world incidence rate of FN among patients with thoracic malignancies that were treated with single-agent amrubicin chemotherapy was 30%. It is suggested that prophylactic G-CSF should be administered during the practical use of single-agent amrubicin chemotherapy for patients who have already received chemotherapy.

PP1 regulatory subunit NIPP1 regulates transcription of E2F1 target genes following DNA damage.

DNA damage induces transcriptional repression of E2F1 target genes and a reduction in histone H3-Thr11 phosphorylation (H3-pThr11 ) at E2F1 target gene promoters. Dephosphorylation of H3-pThr11 is partly mediated by Chk1 kinase and protein phosphatase 1γ (PP1γ) phosphatase. Here, we isolated NIPP1 as a regulator of PP1γ-mediated H3-pThr11 by surveying nearly 200 PP1 interactor proteins. We found that NIPP1 inhibits PP1γ-mediated dephosphorylation of H3-pThr11 both in vivo and in vitro. By generating NIPP1-depleted cells, we showed that NIPP1 is required for cell proliferation and the expression of E2F1 target genes. Upon DNA damage, activated protein kinase A (PKA) phosphorylated the NIPP1-Ser199 residue, adjacent to the PP1 binding motif (RVxF), and triggered the dissociation of NIPP1 from PP1γ, leading to the activation of PP1γ. Furthermore, the inhibition of PKA activity led to the activation of E2F target genes. Statistical analysis confirmed that the expression of NIPP1 was positively correlated with E2F target genes. Taken together, these findings demonstrate that the PP1 regulatory subunit NIPP1 modulates E2F1 target genes by linking PKA and PP1γ during DNA damage.

UV-induced activation of ATR is mediated by UHRF2.

UHRF1 (Ubiquitin-like with PHD and ring finger domains 1) regulates DNA methylation and histone modifications and plays a key role in cell proliferation and the DNA damage response. However, the function of UHRF2, a paralog of UHRF1, in the DNA damage response remains largely unknown. Here, we show that UHRF2 is essential for maintaining cell viability after UV irradiation, as well as for the proliferation of cancer cells. UHRF2 was found to physically interact with ATR in a DNA damage-dependent manner through UHRF2's TTD domain. In addition, phosphorylation of threonine at position 1989, which is required for UV-induced activation of ATR, was impaired in cells depleted of UHRF2, suggesting that UHRF2 is essential in ATR activation. In conclusion, these results suggest a new regulatory mechanism of ATR activation mediated by UHRF2.