Biology subjects

van Mierlo, G.

Publications and source records attributed to van Mierlo, G..

3 recordsLinked to original sources

bioRxiv2020

Unravelling the effect of a potentiating anti-Factor H antibody on atypical hemolytic uremic syndrome associated factor H variants

The complement system plays an important role in our innate immune system. Complement activation results in clearance of pathogens, immune complex and apoptotic cells. The host is protected from complement-mediated damage by several complement regulators. Factor H (FH) is the most important fluid-phase regulator of the alternative pathway of the complement system. Heterozygous mutations in FH are associated with complement-related diseases such as atypical hemolytic uremic syndrome (aHUS) and age-related macular degeneration. We recently described an agonistic anti-FH monoclonal antibody that can potentiate the regulatory function of FH. This antibody could serve as a potential new drug for aHUS patients and alternative to C5 blockade by Eculizumab. However, it is unclear whether this antibody can potentiate FH mutant variants in addition to wild type FH. Here, the functionality and potential of the agonistic antibody in the context of pathogenic aHUS-related FH mutant proteins was investigated. The binding affinity of recombinant WT FH, and the FH variants, W1183L, V1197A, R1210C, and G1194D to C3b was increased upon addition of the potentiating antibody and similarly, the decay accelerating activity of all mutants is increased. The potentiating anti-FH antibody is able to restore the surface regulatory function of most of the tested FH mutants to WT FH levels. In conclusion, our potentiating anti-FH is broadly active and able to enhance both WT FH function as well as most aHUS-associated FH variants tested in this study.

immunology↗

bioRxiv2019

Critical role for P53 in regulating the cell cycle of ground state embryonic stem cells

Mouse Embryonic Stem Cells (ESCs) grown in serum-supplemented conditions are characterized by an extremely short G1-phase due to the lack of G1-phase control. Concordantly, the G1-phase-specific P53-P21 pathway is compromised in serum ESCs. Here we provide evidence that P53 is activated upon transition of serum ESCs to their pluripotent ground state using serum-free 2i conditions and modulates G1-phase progression. Our data shows that the elongated G1-phase characteristic of ground state ESCs is dependent on P53. RNA-seq and ChIP-seq analyses reveal that P53 directly regulates the expression of the Retinoblastoma (RB) protein and that the hypo-phosphorylated, active RB protein plays a key role in G1-phase control. Our findings suggest that the P53-P21 pathway is active in ground state 2i ESCs and that its role in the G1-checkpoint is abolished in serum ESCs. Taken together, the data reveals a mechanism by which inactivation of P53 can lead to loss of RB and uncontrolled cell proliferation.

molecular biology↗

bioRxiv2019

Two distinct functional axes of positive feedback-enforced PRC2 recruitment in mouse embryonic stem cells

Polycomb Repressive Complex 2 (PRC2) plays an essential role in development by catalysing trimethylation of histone H3 lysine 27 (H3K27me3), resulting in gene repression. PRC2 consists of two sub-complexes, PRC2.1 and PRC2.2, in which the PRC2 core associates with distinct ancillary subunits such as MTF2 and JARID2, respectively. Both MTF2, present in PRC2.1, and JARID2, present in PRC2.2, play a role in core PRC2 recruitment to target genes in mouse embryonic stem cells (mESCs). However, it remains unclear how these distinct sub-complexes cooperate to establish Polycomb domains. Here, we combine a range of Polycomb mutant mESCs with chemical inhibition of PRC2 catalytic activity, to systematically dissect their relative contributions to PRC2 binding to target loci. We find that PRC2.1 and PRC2.2 mediate two distinct paths for recruitment, with mutually reinforced binding. Part of the cross-talk between PRC2.1 and PRC2.2 occurs via their catalytic product H3K27me3, which is bound by the PRC2 core-subunit EED, thereby mediating a positive feedback. Strikingly, removal of either JARID2 or H3K27me3 only has a minor effect on PRC2 recruitment, whereas their combined ablation largely attenuates PRC2 recruitment. This strongly suggests an unexpected redundancy between JARID2 and EED-H3K27me3-mediated recruitment of PRC2. Furthermore, we demonstrate that all core PRC2 recruitment occurs through the combined action of MTF2-mediated recruitment of PRC2.1 to DNA and PRC1-mediated recruitment of JARID2-containing PRC2.2. Both axes of binding are supported by EED-H3K27me3 positive feedback, but to a different degree. Finally, we provide evidence that PRC1 and PRC2 mutually reinforce reciprocal binding. Together, these data disentangle the interdependent and cooperative interactions between Polycomb complexes that are important to establish Polycomb repression at target sites.\n\nHighlightsO_LISystematic analysis of Polycomb complex binding to target loci in mESCs using null mutations and chemical inhibition.\nC_LIO_LIPRC1, PRC2.1 and PRC2.2 are all mutually dependent for binding to chromatin, mediated in part by H3K27me3.\nC_LIO_LIPRC2.1 recruitment is dependent on MTF2\nC_LIO_LIPRC2.2 recruitment by JARID2 is dependent on PRC1 and largely redundant with recruitment by H3K27me3\nC_LI

molecular biology↗