BRIT1 protein (also known as MCPH1) contains 3 BRCT domains which are conserved in BRCA1, BRCA2, and other important molecules involved in DNA damage signaling, DNA repair, and tumor suppression. BRIT1 mutations or aberrant expression are found in primary microcephaly patients as well as in cancer patients. Recent in vitro studies suggest that BRIT1/MCPH1 functions as a novel key regulator in the DNA damage response pathways. To investigate its physiological role and dissect the underlying mechanisms, we generated BRIT1 −/− mice and identified its essential roles in mitotic and meiotic recombination DNA repair and in maintaining genomic stability. Both BRIT1 −/− mice and mouse embryonic fibroblasts (MEFs) were hypersensitive to γ-irradiation. BRIT1 −/− MEFs and T lymphocytes exhibited severe chromatid breaks and reduced RAD51 foci formation after irradiation. Notably, BRIT1 −/− mice were infertile and meiotic homologous recombination was impaired. BRIT1-deficient spermatocytes exhibited a failure of chromosomal synapsis, and meiosis was arrested at late zygotene of prophase I accompanied by apoptosis. In mutant spermatocytes, DNA double-strand breaks (DSBs) were formed, but localization of RAD51 or BRCA2 to meiotic chromosomes was severely impaired. In addition, we found that BRIT1 could bind to RAD51/BRCA2 complexes and that, in the absence of BRIT1, recruitment of RAD51 and BRCA2 to chromatin was reduced while their protein levels were not altered, indicating that BRIT1 is involved in mediating recruitment of RAD51/BRCA2 to the damage site. Collectively, our BRIT1-null mouse model demonstrates that BRIT1 is essential for maintaining genomic stability in vivo to protect the hosts from both programmed and irradiation-induced DNA damages, and its depletion causes a failure in both mitotic and meiotic recombination DNA repair via impairing RAD51/BRCA2's function and as a result leads to infertility and genomic instability in mice.

Double strand breaks (DSBs) are the most deleterious of the DNA lesions that initiate genomic instability and promote tumorigenesis. Cells have evolved a complex protein network to detect, signal, and repair DSBs. In mammalian cells, a key component in this network is H2AX, which becomes rapidly phosphorylated at Ser 139 (␥-H2AX) at DSBs. Here we show that monoubiquitination of H2AX mediated by the RNF2-BMI1 complex is critical for the efficient formation of ␥-H2AX and functions as a proximal regulator in DDR (DNA damage response). RNF2-BMI1 interacts with H2AX in a DNA damagedependent manner and is required for monoubiquitination of H2AX at Lys 119 /Lys 120 . As a functional consequence, we show that the H2AX K120R mutant abolishes H2AX monoubiquitination, impairs the recruitment of p-ATM (Ser 1981 ) to DSBs, and thereby reduces the formation of ␥-H2AX and the recruitment of MDC1 to DNA damage sites. These data suggest that monoubiquitination of H2AX plays a critical role in initiating DNA damage signaling. Consistent with these observations, impairment of RNF2-BMI1 function by siRNA knockdown or overexpression of the ligase-dead RNF2 mutant all leads to significant defects both in accumulation of ␥-H2AX, p-ATM, and MDC1 at DSBs and in activation of NBS1 and CHK2. Additionally, the regulatory effect of RNF2-BMI1 on ␥-H2AX formation is dependent on ATM. Lacking their ability to properly activate the DNA damage signaling pathway, RNF2-BMI1 complex-depleted cells exhibit impaired DNA repair and increased sensitivity to ionizing radiation. Together, our findings demonstrate a distinct monoubiquitination-dependent mechanism that is required for H2AX phosphorylation and the initiation of DDR. Double strand break (DSB)3 formation in cells immediately triggers the recruitment of DNA damage signaling and repair proteins to the damaged loci, where these proteins form discrete nuclear foci (ionizing radiation (IR)-induced foci). The order and timing of the recruitment of DDR proteins is critical for detection, signaling, and repair of DSBs, which is necessary to maintain genomic stability (1, 2).One of the initial events occurring at DNA damage loci is phosphorylation of H2AX, a histone H2A variant, at Ser 139 of its carboxyl-terminal tail (␥-H2AX) by one or more members of the PI3K-like kinase group, including ATM, ATR, and DNA-PK (3-5). ␥-H2AX decorates the chromatin flanking DSBs and recruits many early DDR proteins, such as MDC1 and BRIT1 (also known as MCPH1), to generate IR-induced foci (6 -10).In addition to phosphorylation of H2AX, ubiquitination of H2AX is an important epigenetic marker for DNA lesions in DDR (11-13). Recent studies have highlighted the function of RING-finger ubiquitin ligases RNF8 and RNF168 in promoting accumulation of repair proteins at DSBs in an MDC1-dependent manner (14 -19). As expected, accumulating in vitro and in vivo studies have demonstrated that modifications of H2AX play a central role in regulating various cellular responses to DSBs, including DNA repair, cell cycle checkpoints, ...

Tumor microenvironment (TME) is a specialized ecosystem of host components, designed by tumor cells for successful development and metastasis of tumor. With the advent of 3D culture and advanced bioinformatic methodologies, it is now possible to study TME’s individual components and their interplay at higher resolution. Deeper understanding of the immune cell’s diversity, stromal constituents, repertoire profiling, neoantigen prediction of TMEs has provided the opportunity to explore the spatial and temporal regulation of immune therapeutic interventions. The variation of TME composition among patients plays an important role in determining responders and non-responders towards cancer immunotherapy. Therefore, there could be a possibility of reprogramming of TME components to overcome the widely prevailing issue of immunotherapeutic resistance. The focus of the present review is to understand the complexity of TME and comprehending future perspective of its components as potential therapeutic targets. The later part of the review describes the sophisticated 3D models emerging as valuable means to study TME components and an extensive account of advanced bioinformatic tools to profile TME components and predict neoantigens. Overall, this review provides a comprehensive account of the current knowledge available to target TME.

Jun activation domain-binding protein 1 (JAB1) is a multifunctional protein that participates in the control cell proliferation and the stability of multiple proteins. JAB1 overexpression has been implicated in the pathogenesis of human cancer. JAB1 regulates several key proteins and thereby produces varied effects on cell cycle progression, genome stability, and cell survival. However, the biological significance of JAB1 activity in these cellular signaling pathways is unclear. Therefore, we developed mice that were deficient in Jab1 and analyzed the null embryos and heterozygous cells. This disruption of Jab1 in mice resulted in early embryonic lethality due to accelerated apoptosis. Loss of Jab1 expression sensitized both mouse primary embryonic fibroblasts and osteosarcoma cells to gamma radiation–induced apoptosis, with an increase in spontaneous DNA damage and homologous recombination (HR) defects, both of which correlated with reduced levels of the DNA repair protein Rad51 and elevated levels of p53. Furthermore, the accumulated p53 directly binds to Rad51 promoter, inhibited its activity, and represent a major mechanism underlying the HR repair defect in Jab1-deficient cells. These results indicate that Jab1 is essential for efficient DNA repair and mechanistically link Jab1 to the maintenance of genome integrity and to cell survival.

Cancer is intimately related to the accumulation of DNA damage, and repair failures (including mutation prone repair and hyperactive repair systems). This article relates current clinical categories for breast cancer and their common DNA damage repair defects. Information is included on the potential for accumulation of DNA damage in the breast tissue of a woman during her lifetime and the role of DNA damage in breast cancer development. We then cover endogenous and exogenous sources of DNA damage, types of DNA damage repair and basic signal transduction pathways for three gene products involved in the DNA damage response system; namely BRCA1, BRIT1 and PARP-1. These genes are often considered tumor suppressors because of their roles in DNA damage response and some are under clinical investigation as likely sources for effective new drugs to treat breast cancers. Finally we discuss some of the problems of DNA damage repair systems in cancer and the conundrum of hyper-active repair systems which can introduce mutations and confer a survival advantage to certain types of cancer cells.

MCPH1, also known as BRIT1, has recently been identified as a novel key regulatory gene of the DNA damage response pathway. MCPH1 is located on human chromosome 8p23.1, where human cancers frequently show loss of heterozygosity. As such, MCPH1 is aberrantly expressed in many malignancies, including breast and ovarian cancers, and the function of MCPH1 has been implicated in tumor suppression. However, it remains poorly understood whether MCPH1 deficiency leads to tumorigenesis. Here, we generated and studied both Mcph1−/− and Mcph1−/−p53−/− mice; we showed that Mcph1−/− mice developed tumors with long latency, and that primary lymphoma developed significantly earlier in Mcph1−/−p53−/− mice than in Mcph11+/+p53−/− and Mcph1+/−p53−/− mice. The Mcph1−/−p53−/− lymphomas and derived murine embryonic fibroblasts (MEFs) were both more sensitive to irradiation. Mcph1 deficiency resulted in remarkably increased chromosome and chromatid breaks in Mcph1−/− p53−/− lymphomas and MEFs, as determined by metaphase spread assay and spectral karyotyping analysis. Additionally, Mcph1 deficiency significantly enhanced aneuploidy as well as abnormal centrosome multiplication in Mcph1−/−p53−/− cells. Meanwhile, Mcph1 deficiency impaired double strand break (DSB) repair in Mcph1−/−p53−/− MEFs as demonstrated by neutral Comet assay. Compared with Mcph1+/+p53−/− MEFs, homologous recombination and non-homologous end joining activities were significantly decreased in Mcph1−/−p53−/− MEFs. Notably, reconstituted MCPH1 rescued the defects of DSB repair and alleviated chromosomal aberrations in Mcph1−/−p53−/− MEFs. Taken together, our data demonstrate MCPH1 deficiency promotes genomic instability and increases cancer susceptibility. Our study using knockout mouse models provides convincing genetic evidence that MCPH1 is a bona fide tumor suppressor gene. Its deficiency leading to defective DNA repair in tumors can be utilized to develop novel targeted cancer therapies in the future.

Vaccination against COVID-19 is critical for immuno-compromised individuals, including patients with cancer. Systemic reactogenicity, a manifestation of the innate immune response to vaccines, occurs in up to 69% of patients following vaccination with RNA-based COVID-19 vaccines. Tumor regression can occur following an intense immune-inflammatory response and novel strategies to treat cancer rely on manipulating the host immune system. Here, we report spontaneous regression of metastatic salivary gland myoepithelial carcinoma in a patient who experienced grade 3 systemic reactogenicity, following vaccination with the mRNA-1273 COVID-19 vaccine. Histological and immunophenotypic inspection of the postvaccination lung biopsy specimens showed a massive inflammatory infiltrate with scant embedded tumor clusters (<5%). Highly multiplexed imaging mass cytometry showed that the postvaccination lung metastasis samples had remarkable immune cell infiltration, including CD4+ T cells, CD8+ T cells, natural killer cells, B cells, and dendritic cells, which contrasted with very low levels of these cells in the prevaccination primary tumor and lung metastasis samples. CT scans obtained 3, 6, and 9 months after the second vaccine dose demonstrated persistent tumor shrinkage (50%, 67%, and 73% reduction, respectively), suggesting that vaccination stimulated anticancer immunity. Insight: This case suggests that the mRNA-1273 COVID-19 vaccine stimulated anticancer immunity and tumor regression.

In past decades, cancer patient survival has been improved with earlier detection and advancements in therapy. However, many patients who exhibit no clinical symptoms after frontline therapy subsequently suffer, often many years later, aggressive tumor recurrence. Cancer recurrence represents a critical clinical challenge in effectively treating malignancies and for patients’ quality of life. Tumor cell dormancy may help to explain treatment resistance and recurrence or metastatic reactivation. Understanding the dormant stage of tumor cells may help in discovering ways to maintain the dormant state or permanently eliminate dormant residual disseminated tumor cells. Over the past decade, numerous studies indicate that various mechanisms of tumor dormancy exist, including cellular dormancy (quiescence), angiogenic dormancy, and immunologic dormancy. In this short review, we summarize recent experimental and clinical evidence for these three mechanisms and other possible tumor microenvironment mechanisms that may influence tumor dormancy.