Prospect of reprogramming replication licensing for cancer drug development

An essential Noc3p dimerization cycle mediates ORC double-hexamer formation in replication licensing

Replication licensing, a prerequisite of DNA replication, helps to ensure once-per-cell-cycle genome duplication. Some DNA replication-initiation proteins are sequentially loaded onto replication origins to form pre-replicative complexes (pre-RCs). ORC and Noc3p bind replication origins throughout the cell cycle, providing a platform for pre-RC assembly. We previously reported that cell cycle-dependent ORC dimerization is essential for the chromatin loading of the symmetric MCM double-hexamers. Here, we used Saccharomyces cerevisiae separation-of-function NOC3 mutants to confirm the separable roles of Noc3p in DNA replication and ribosome biogenesis. We also show that an essential and cell cycle-dependent Noc3p dimerization cycle regulates the ORC dimerization cycle. Noc3p dimerizes at the M-to-G1 transition and de-dimerizes in S-phase. The Noc3p dimerization cycle coupled with the ORC dimerization cycle enables replication licensing, protects nascent sister replication origins after replication initiation, and prevents re-replication. This study has revealed a new mechanism of replication licensing and elucidated the molecular mechanism of Noc3p as a mediator of ORC dimerization in pre-RC formation.

MCM2 in human cancer: functions, mechanisms, and clinical significance

Background

Aberrant DNA replication is the main source of genomic instability that leads to tumorigenesis and progression. MCM2, a core subunit of eukaryotic helicase, plays a vital role in DNA replication. The dysfunction of MCM2 results in the occurrence and progression of multiple cancers through impairing DNA replication and cell proliferation.

Conclusions

MCM2 is a vital regulator in DNA replication. The overexpression of MCM2 was detected in multiple types of cancers, and the dysfunction of MCM2 was correlated with the progression and poor prognoses of malignant tumors. According to the altered expression of MCM2 and its correlation with clinicopathological features of cancer patients, MCM2 was thought to be a sensitive biomarker for cancer diagnosis, prognosis, and chemotherapy response. The anti-tumor effect induced by MCM2 inhibition implies the potential of MCM2 to be a novel therapeutic target for cancer treatment. Since DNA replication stress, which may stimulate anti-tumor immunity, frequently occurs in MCM2 deficient cells, it also proposes the possibility that MCM2 targeting improves the effect of tumor immunotherapy.

LCAT1 is an oncogenic LncRNA by stabilizing the IGF2BP2-CDC6 axis

Long non-coding RNAs (lncRNAs) is known to play vital roles in modulating tumorigenesis. We previously reported that LCAT1, a novel lncRNA, promotes the growth and metastasis of lung cancer cells both in vitro and in vivo. However, the underlying mechanism(s) of LCAT1 as an oncogenic regulator remains elusive. Here, we showed that LCAT1 physically interacts with and stabilizes IGF2BP2, an m⁶A reader protein, by preventing its degradation via autolysosomes. IGF2BP2 is overexpressed in lung cancer tissues, which is associated with poor survival of non-small cell lung cancer patients, suggesting its oncogenic role. Biologically, IGF2BP2 depletion inhibits growth and survival as well as the migration of lung cancer cells. Mechanistically, the LCAT1/IGF2BP2 complex increased the levels of CDC6, a key cell cycle regulator, by stabilizing its mRNA in an m⁶A-dependent manner. Like IGF2BP2, CDC6 is also overexpressed in lung cancer tissues with poor patient survival, and CDC6 knockdown has oncogenic inhibitory activity. Taken together, the LCAT1-IGF2BP2-CDC6 axis appears to play a vital role in promoting the growth and migration of lung cancer cells, and is a potential therapeutic target for lung cancer. Importantly, our finding also highlights a previously unknown critical role of LCAT1 in m⁶A-dependent gene regulation by preventing autolytic degradation of IGF2BP2.

Cryo-EM structure of human hexameric MCM2-7 complex

The central step in the initiation of eukaryotic DNA replication is the loading of the minichromosome maintenance 2–7 (MCM2-7) complex, the core of the replicative DNA helicase, onto chromatin at replication origin. Here, we reported the cryo-EM structure of endogenous human single hexameric MCM2-7 complex with a resolution at 4.4 Å, typically an open-ring hexamer with a gap between Mcm2 and Mcm5. Strikingly, further analysis revealed that human MCM2-7 can self-associate to form a loose double hexamer which potentially implies a novel mechanism underlying the MCM2-7 loading in eukaryote. The high-resolution cryo-EM structure of human MCM2-7 is critical for understanding the molecular mechanisms governing human DNA replication, especially the MCM2-7 chromatin loading and pre-replicative complex assembly.

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A Twin-Strep-Tag II tag was fused to Mcm4 by using CRISPR-Cas9 technique

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The endogenous human MCM2-7 complex was successfully purified

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The high-resolution cryo-EM structure of human hexameric MCM2-7 complex

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The human single MCM2-7 hexamer can self-associate to form a double hexamer

GREB1L as a candidate gene of Mayer-Rokitansky-Küster-Hauser Syndrome

Mayer-Rokitansky-Küster-Hauser (MRKH) Syndrome is a sex development disorder that affects 1 in every 4500 46, XX live births. At least a subset of MRKH syndrome is genetically related to which various candidate genes have been identified. The growth regulation by estrogen in breast cancer 1-like gene (GREB1L) is an androgen-regulated gene reported to be a co-activator of the retinoic acid receptor gene (RAR). Thus expression levels of GREB1L have implications on renal system cellular differentiation, morphogenesis, and homeostasis in vertebrates. Variants of GREB1L have been reported in familial and sporadic MRKH Syndrome and more importantly, in a three-generation family ofMRKH syndrome propositae. Much the same way, Mutants of GREB1L have also been identified in isolated bilateral renal agenesis and deafness both of which are extra-genital tract anomalies in MRKH type 2. Again, renal agenesis transgenic mice have been produced from an E13.5 CRISPR/cas9 GREB1L mutagenesis. Though no GREB1L mutation has been reported in cardiac malformation, there is evidence that GREB1L is involved in ventricular development. Here, we intorigate evidence that projects GREB1L as a candidate gene of Mayer-Rokitansky-Küster-Hauser Syndrome and propose that functional validation analysis to that effect is imparative.