Microcephalin guards against small brains, genetic instability, and cancer

Silencing BRIT1 Facilitates the Abilities of Invasiveness and Migration in Trophoblast Cells

Background

The improper invasion of trophoblast cells (TC) can cause various diseases. BRCT-repeat inhibitor of hTERT expression (BRIT1) is involved in the invasion of tumors. Here, we analyzed the effects of BRIT1 on the invasion of TC.

Material/Methods

The expression of BRIT1 in JEG-3, B6Tert, and HTR8/SVneo cells was evaluated by transcription-quantitative polymerase chain reaction (RT-qPCR) and Western blotting. The viability, invasion, and migration of HTR8/SVneo cells were measured using cell counting kit-8 (CCK-8) and Transwell assays. The activities of pro-matrix metalloproteinase-2 (pro-MMP-2) and pro-MMP-9 were tested by gelatin zymography assay. The levels of invasion- and Wnt/β-catenin pathway-related factors were assessed by RT-qPCR and Western blotting.

Results

Levels of BRIT1 in HTR8/SVneo cells were higher than that of JEG-3 and B6Tert cells. The transfection efficiency of BRIT1 siRNA-2 was better than BRIT1 siRNA-1 in HTR8/SVneo cells. BRIT1 siRNA-2 did not change cell viability, whereas it promoted cell invasion and migration. BRIT1 siRNA-2 enhanced the activities of pro-MMP-2 and pro-MMP-9, as well MMP-2 and MMP-9 levels, and reduced tissue inhibitor of metalloproteinases-1 (TIMP-1) and TIMP-2 expression. Moreover, BRIT1 siRNA-2 significantly increased the levels of Wnt2, Wnt3, and β-catenin.

Conclusions

BRIT1 silencing accelerated the invasion and migration of TC and activated the Wnt/β-catenin pathway. Our results may provide new insights for finding new molecular targets to cure disease caused by insufficient invasion of TC.

Dual recognition of phosphoserine and phosphotyrosine in histone variant H2A.X by DNA damage response protein MCPH1

Tyr142, the C-terminal amino acid of histone variant H2A.X is phosphorylated by WSTF (Williams-Beuren syndrome transcription factor), a component of the WICH complex (WSTF-ISWI chromatin-remodeling complex), under basal conditions in the cell. In response to DNA double-strand breaks (DSBs), H2A.X is instantaneously phosphorylated at Ser139 by the kinases ATM and ATR and is progressively dephosphorylated at Tyr142 by the Eya1 and Eya3 tyrosine phosphatases, resulting in a temporal switch from a postulated diphosphorylated (pSer139, pTyr142) to monophosphorylated (pSer139) H2A.X state. How mediator proteins interpret these two signals remains a question of fundamental interest. We provide structural, biochemical, and cellular evidence that Microcephalin (MCPH1), an early DNA damage response protein, can read both modifications via its tandem BRCA1 C-terminal (BRCT) domains, thereby emerging as a versatile sensor of H2A.X phosphorylation marks. We show that MCPH1 recruitment to sites of DNA damage is linked to both states of H2A.X.

ASPM and microcephalin expression in epithelial ovarian cancer correlates with tumour grade and survival

BACKGROUND

The clinico-pathological and molecular heterogeneity of epithelial ovarian cancer (EOC) complicates its early diagnosis and successful treatment. Highly aneuploid tumours and the presence of ascitic fluids are hallmarks of EOC. Two microcephaly-associated proteins, abnormal spindle-like microcephaly-associated protein (ASPM) and microcephalin, are involved in mitosis and DNA damage repair. Their expression is deregulated at the RNA level in EOC. Here, ASPM and microcephalin protein expression in primary cultures established from the ascites of patients with EOC was determined and correlated with clinical data to assess their suitability as biomarkers.

METHODS

Five established ovarian cancer cell lines, cells derived from two benign ovarian ascites samples and 40 primary cultures of EOC derived from ovarian ascites samples were analysed by protein slot blotting and/or immunofluorescence to determine ASPM and microcephalin protein levels and their cellular localisation. Results were correlated with clinico-pathological data.

RESULTS

A statistically significant correlation was identified for ASPM localisation and tumour grade, with high levels of cytoplasmic ASPM correlating with grade 1 tumours. Conversely, cytoplasmic microcephalin was only identified in high-grade tumours. Furthermore, low levels of nuclear microcephalin correlated with reduced patient survival.

CONCLUSION

Our results suggest that ASPM and microcephalin have the potential to be biomarkers in ovarian cancer.

Cell cycle control of mammalian neural stem cells: putting a speed limit on G1

The potential to increase unlimitedly in number and to generate differentiated cell types is a key feature of somatic stem cells. Within the nervous system, cellular and environmental determinants tightly control the expansion and differentiation of neural stem cells. Importantly, a number of studies have indicated that changes in cell cycle length can influence development and physiopathology of the nervous system, and might have played a role during evolution of the mammalian brain. Specifically, it has been suggested that the length of G1 can directly influence the differentiation of neural precursors. This has prompted the proposal of a model to explain how manipulation of G1 length can be used to expand neural stem cells. If validated in non-neural systems, this model might provide the means to control the proliferation vs. differentiation of somatic stem cells, which will represent a significant advance in the field.

Loss of ATRX leads to chromosome cohesion and congression defects

Alpha thalassemia/mental retardation X linked (ATRX) is a switch/sucrose nonfermenting-type ATPase localized at pericentromeric heterochromatin in mouse and human cells. Human ATRX mutations give rise to mental retardation syndromes characterized by developmental delay, facial dysmorphisms, cognitive deficits, and microcephaly and the loss of ATRX in the mouse brain leads to reduced cortical size. We find that ATRX is required for normal mitotic progression in human cultured cells and in neuroprogenitors. Using live cell imaging, we show that the transition from prometaphase to metaphase is prolonged in ATRX-depleted cells and is accompanied by defective sister chromatid cohesion and congression at the metaphase plate. We also demonstrate that loss of ATRX in the embryonic mouse brain induces mitotic defects in neuroprogenitors in vivo with evidence of abnormal chromosome congression and segregation. These findings reveal that ATRX contributes to chromosome dynamics during mitosis and provide a possible cellular explanation for reduced cortical size and abnormal brain development associated with ATRX deficiency.

Viral regulation of aquaporin 4, connexin 43, microcephalin and nucleolin

The current study investigated whether human influenza viral infection in midpregnancy leads to alterations in proteins involved in brain development. Human influenza viral infection was administered to E9 pregnant Balb/c mice. Brains of control and virally-exposed littermates were subjected to microarray analysis, SDS-PAGE and western blotting at three postnatal stages. Microarray analysis of virally-exposed mouse brains showed significant, two-fold change in expression of multiple genes in both neocortex and cerebellum when compared to sham-infected controls. Levels of mRNA and protein levels of four selected genes were examined in brains of exposed mice. Nucleolin mRNA was significantly decreased in day 0 and day 35 neocortex and significantly increased in day 35 cerebellum. Protein levels were significantly upregulated at days 35 and 56 in neocortex and at day 56 in cerebellum. Connexin 43 protein levels were significantly decreased at day 56 in neocortex. Aquaporin 4 mRNA was significantly decreased in day 0 neocortex. Aquaporin 4 protein levels decreased in neocortex significantly at day 35. Finally, microcephalin mRNA was significantly decreased in day 56 neocortex and protein levels were significantly decreased at 56 cerebellum. These data suggest that influenza viral infection in midpregnancy in mice leads to long-term changes in brain markers for enhanced ribosome genesis (nucleolin), increased production of immature neurons (microcephalin), and abnormal glial-neuronal communication and neuron migration (connexin 43 and aquaporin 4).

TheDrosophilahomolog ofMCPH1,a human microcephaly gene, is required for genomic stability in the early embryo

Mutation of human microcephalin (MCPH1) causes autosomal recessive primary microcephaly, a developmental disorder characterized by reduced brain size. We identified mcph1, the Drosophila homolog of MCPH1, in a genetic screen for regulators of S-M cycles in the early embryo. Embryos of null mcph1 female flies undergo mitotic arrest with barrel-shaped spindles lacking centrosomes. Mutation of Chk2 suppresses these defects, indicating that they occur secondary to a previously described Chk2-mediated response to mitotic entry with unreplicated or damaged DNA. mcph1 embryos exhibit genomic instability as evidenced by frequent chromatin bridging in anaphase. In contrast to studies of human MCPH1, the ATR/Chk1-mediated DNA checkpoint is intact in Drosophila mcph1 mutants. Components of this checkpoint, however, appear to cooperate with MCPH1 to regulate embryonic cell cycles in a manner independent of Cdk1 phosphorylation. We propose a model in which MCPH1 coordinates the S-M transition in fly embryos: in the absence of mcph1, premature chromosome condensation results in mitotic entry with unreplicated DNA, genomic instability, and Chk2-mediated mitotic arrest. Finally, brains of mcph1 adult male flies have defects in mushroom body structure, suggesting an evolutionarily conserved role for MCPH1 in brain development.