SETD4-mediated KU70 methylation suppresses apoptosis

The Mammalian KU70 C-terminus SAP Domain Is Required to Repair Exogenous DNA Damage

The mammalian non-homologous end joining (NHEJ) is required for V(D)J recombination as well as coping with exogenously induced DNA double strand breaks (DSBs). Initiated by the binding of KU70/KU80 (KU) dimer to DNA ends and the subsequent recruitment of the DNA- dependent protein kinase catalytic subunit (DNA-PKcs), NHEJ plays a key role in DNA repair. While there has been significant structural understandings of how KU70 participates in NHEJ, the specific function of its highly conserved C-terminal SAP domain remains elusive. In this study, we developed a novel mouse model by deleting the SAP domain but preserving the KU70 nuclear localization and its dimerization ability with KU80. We found that the KU70 SAP deletion did not affect the V(D)J recombination or animal development but significantly impaired the animals and cells in repairing exogenously induced DSBs. We further showed an inability of KU70-ΔSAP cells to retain the DNA Ligase IV (LIG4) and other NHEJ co-factors on chromatin, and a spreading pattern of DSB marker γH2AX in KU70-ΔSAP cells after DNA damage. Our findings suggest that a specific inhibition of the SAP function may offer an opportunity to modulate cell sensitivity to therapeutic DSB-inducing agents without interfering with the developmental function of KU70.

KeyPoints

Generation of a novel transgenic mouse line lacking the C-terminal conserved KU70-SAP domainKU70-SAP defends against exogenous DSBs, but unessential for development and V(D)J recombinationKU70-SAP aids in recruiting and retaining NHEJ components, such as LIG4, to DSB sites.

Molecular cloning, subcellular localization, and rapid recruitment to DNA damage sites of chicken Ku70

Ku70 is a multifunctional protein with pivotal roles in DNA repair via non-homologous end-joining, V(D)J recombination, telomere maintenance, and neuronal apoptosis control. Nonetheless, its regulatory mechanisms remain elusive. Chicken Ku70 (GdKu70) cDNA has been previously cloned, and DT40 cells expressing it have significantly contributed to critical biological discoveries. GdKu70 features an additional 18 amino acids at its N-terminus compared to mammalian Ku70, the biological significance of which remains uncertain. Here, we show that the 5' flanking sequence of GdKu70 cDNA is not nearly encoded in the chicken genome. Notably, these 18 amino acids result from fusion events involving the NFE2L1 gene on chromosome 27 and the Ku70 gene on chromosome 1. Through experiments using newly cloned chicken Ku70 cDNA and specific antibodies, we demonstrated that Ku70 localizes within the cell nucleus as a heterodimer with Ku80 and promptly accumulates at DNA damage sites following injury. This suggests that the functions and spatiotemporal regulatory mechanisms of Ku70 in chickens closely resemble those in mammals. The insights and resources acquired will contribute to elucidate the various mechanisms by which Ku functions. Meanwhile, caution is advised when interpreting the previous numerous key studies that relied on GdKu70 cDNA and its expressing cells.

SETD4 inhibits prostate cancer development by promoting H3K27me3-mediated NUPR1 transcriptional repression and cell cycle arrest

The suppressor of variegation enhancer of zeste-trithorax (SET) domain methyltransferases have been reported to function as key regulators in multiple tumor types by catalyzing histone lysine methylation. Nevertheless, our understanding on the role of these lysine methyltransferases, including SETD4, in prostate cancer (PCa) remains limited. Hence, the specific role of SETD4 in PCa was investigated in this study. The expression of SETD4 in PCa cells and tissue samples was downregulated in PCa cells and tissue specimens, and decreased SETD4 expression led to inferior clinicopathological characteristics in patients with PCa. knockdown of SETD4 facilitated the proliferation of PCa cells and accelerated cell cycle progression. Mechanistically, SETD4 repressed NUPR1 transcription by methylating H3K27 to generate H3K27me3, subsequently inactivated Akt pathway and impeded the tumorigenesis of PCa. Our results highlight that SETD4 prevents the development of PCa by catalyzing the methylation of H3K27 and suppressing NUPR1 transcription, subsequently inactivating the Akt signaling pathway. The findings suggest the potential application of SETD4 in PCa prognosis and therapeutics.

From ecology to oncology: To understand cancer stem cell dormancy, ask a Brine shrimp (Artemia)

The brine shrimp (Artemia), releases embryos that can remain dormant for up to a decade. Molecular and cellular level controlling factors of dormancy in Artemia are now being recognized or applied as active controllers of dormancy (quiescence) in cancers. Most notably, the epigenetic regulation by SET domain-containing protein 4 (SETD4), is revealed as highly conserved and the primary control factor governing the maintenance of cellular dormancy from Artemia embryonic cells to cancer stem cells (CSCs). Conversely, DEK, has recently emerged as the primary factor in the control of dormancy exit/reactivation, in both cases. The latter has been now successfully applied to the reactivation of quiescent CSCs, negating their resistance to therapy and leading to their subsequent destruction in mouse models of breast cancer, without recurrence or metastasis potential. In this review, we introduce the many mechanisms of dormancy from Artemia ecology that have been translated into cancer biology, and herald Artemia's arrival on the model organism stage. We show how Artemia studies have unlocked the mechanisms of the maintenance and termination of cellular dormancy. We then discuss how the antagonistic balance of SETD4 and DEK fundamentally controls chromatin structure and consequently governs CSCs function, chemo/radiotherapy resistance, and dormancy in cancers. Many key stages from transcription factors to small RNAs, tRNA trafficking, molecular chaperones, ion channels, and links with various pathways and aspects of signaling are also noted, all of which link studies in Artemia to those of cancer on a molecular and/or cellular level. We particularly emphasize that the application of such emerging factors as SETD4 and DEK may open new and clear avenues for the treatment for various human cancers.

Unmasking the mammalian SET domain-containing protein 4

SET domain-containing protein 4 (SETD4) is a member of a unique class of protein lysine methyltransferases. Here, we introduce the basic features of SETD4 and summarize the key findings from recent studies with emphases on its roles in tissue development and tumorigenesis, and its methylation substrates. SETD4 is expressed in stem/progenitor cells. Ablation of Setd4⁺ cells impedes the repopulation of acinar cells after pancreatic injury. Setd4 deletion in mice promotes the recovery of radiation-induced bone marrow (BM) failure by boosting the function of BM niche, facilitates the generation of endothelial cells and neovascularization of capillary vessels in the heart, enhances the proliferation of BM mesenchymal stem cells and disrupts the TLR4 signaling in BM-derived macrophages. SETD4 expression is also associated with the maintenance of quiescent breast cancer stem cells. While mouse Setd4 knockout delays radiation-induced T-lymphoma formation, elevated SETD4 expression has been observed in some proliferative cancer cells and is associated with a pro-survival potential. Oncogenic fusions of SETD4 have also been identified in cancer, albeit rare. In addition, SETD4 methylates lysine-570 in the C-terminal globular domain of KU70, which enables KU70 translocation to cytoplasm to suppress apoptosis.