Publications by authors named "Lama AlAbdi"

6 Publications

  • Page 1 of 1

Exploiting the Autozygome to Support Previously Published Mendelian Gene-Disease Associations: An Update.

Front Genet 2020 31;11:580484. Epub 2020 Dec 31.

Department of Genetics, King Faisal Specialist Hospital and Research Center, Riyadh, Saudi Arabia.

There is a growing interest in standardizing gene-disease associations for the purpose of facilitating the proper classification of variants in the context of Mendelian diseases. One key line of evidence is the independent observation of pathogenic variants in unrelated individuals with similar phenotypes. Here, we expand on our previous effort to exploit the power of autozygosity to produce homozygous pathogenic variants that are otherwise very difficult to encounter in the homozygous state due to their rarity. The identification of such variants in genes with only tentative associations to Mendelian diseases can add to the existing evidence when observed in the context of compatible phenotypes. In this study, we report 20 homozygous variants in 18 genes (, and ) that satisfy the ACMG classification for pathogenic/likely pathogenic if the involved genes had confirmed rather than tentative links to diseases. These variants were selected because they were truncating, founder with compelling segregation or supported by robust functional assays as with the variant that we present its validation using yeast model. Our findings support the previously reported disease associations for these genes and represent a step toward their confirmation.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3389/fgene.2020.580484DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7806527PMC
December 2020

The acute myeloid leukemia variant DNMT3A Arg882His is a DNMT3B-like enzyme.

Nucleic Acids Res 2020 04;48(7):3761-3775

Department of Biochemistry, Purdue University, West Lafayette, IN 47907, USA.

We have previously shown that the highly prevalent acute myeloid leukemia (AML) mutation, Arg882His, in DNMT3A disrupts its cooperative mechanism and leads to reduced enzymatic activity, thus explaining the genomic hypomethylation in AML cells. However, the underlying cause of the oncogenic effect of Arg882His in DNMT3A is not fully understood. Here, we discovered that DNMT3A WT enzyme under conditions that favor non-cooperative kinetic mechanism as well as DNMT3A Arg882His variant acquire CpG flanking sequence preference akin to that of DNMT3B, which is non-cooperative. We tested if DNMT3A Arg882His could preferably methylate DNMT3B-specific target sites in vivo. Rescue experiments in Dnmt3a/3b double knockout mouse embryonic stem cells show that the corresponding Arg878His mutation in mouse DNMT3A severely impairs its ability to methylate major satellite DNA, a DNMT3A-preferred target, but has no overt effect on the ability to methylate minor satellite DNA, a DNMT3B-preferred target. We also observed a previously unappreciated CpG flanking sequence bias in major and minor satellite repeats that is consistent with DNMT3A and DNMT3B specificity suggesting that DNA methylation patterns are guided by the sequence preference of these enzymes. We speculate that aberrant methylation of DNMT3B target sites could contribute to the oncogenic potential of DNMT3A AML variant.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1093/nar/gkaa139DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7144950PMC
April 2020

Oct4-Mediated Inhibition of Lsd1 Activity Promotes the Active and Primed State of Pluripotency Enhancers.

Cell Rep 2020 02;30(5):1478-1490.e6

Department of Biochemistry, Purdue University, West Lafayette, IN 47907, USA; Purdue University Center for Cancer Research, Purdue University, West Lafayette, IN 47907, USA. Electronic address:

An aberrant increase in pluripotency gene (PpG) expression due to enhancer reactivation could induce stemness and enhance the tumorigenicity of cancer stem cells. Silencing of PpG enhancers (PpGe) during embryonic stem cell differentiation involves Lsd1-mediated H3K4me1 demethylation and DNA methylation. Here, we observed retention of H3K4me1 and DNA hypomethylation at PpGe associated with a partial repression of PpGs in F9 embryonal carcinoma cells (ECCs) post-differentiation. H3K4me1 demethylation in F9 ECCs could not be rescued by Lsd1 overexpression. Given our observation that H3K4me1 demethylation is accompanied by strong Oct4 repression in P19 ECCs, we tested if Oct4 interaction with Lsd1 affects its catalytic activity. Our data show a dose-dependent inhibition of Lsd1 activity by Oct4 and retention of H3K4me1 at PpGe in Oct4-overexpressing P19 ECCs. These data suggest that Lsd1-Oct4 interaction in cancer stem cells could establish a "primed" enhancer state that is susceptible to reactivation, leading to aberrant PpG expression.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.celrep.2019.11.040DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7316367PMC
February 2020

The transcription factor Vezf1 represses the expression of the antiangiogenic factor Cited2 in endothelial cells.

J Biol Chem 2018 07 24;293(28):11109-11118. Epub 2018 May 24.

From the Department of Biochemistry and

Formation of the vasculature by angiogenesis is critical for proper development, but angiogenesis also contributes to the pathogenesis of various disorders, including cancer and cardiovascular diseases. Vascular endothelial zinc finger 1 (Vezf1), is a Krüppel-like zinc finger protein that plays a vital role in vascular development. However, the mechanism by which Vezf1 regulates this process is not fully understood. Here, we show that mouse embryonic stem cells (ESC) have significantly increased expression of a stem cell factor, Cbp/p300-interacting transactivator 2 (Cited2). Compared with WT ESCs, ESCs inefficiently differentiated into endothelial cells (ECs), which exhibited defects in the tube-formation assay. These defects were due to reduced activation of EC-specific genes concomitant with lower enrichment of histone 3 acetylation at Lys (H3K27) at their promoters. We hypothesized that overexpression of Cited2 in cells sequesters P300/CBP away from the promoters of proangiogenic genes and thereby contributes to defective angiogenesis in these cells. This idea was supported by the observation that shRNA-mediated depletion of Cited2 significantly reduces the angiogenic defects in the ECs. In contrast to previous studies that have focused on the role of Vezf1 as a transcriptional activator of proangiogenic genes, our findings have revealed a role for Vezf1 in modulating the expression of the antiangiogenic factor Cited2. Vezf1 previously has been characterized as an insulator protein, and our results now provide insights into the mechanism, indicating that Vezf1 can block inappropriate, nonspecific interactions of promoters with -located enhancers, preventing aberrant promoter activation.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1074/jbc.RA118.002911DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6052231PMC
July 2018

Dnmt3b Methylates DNA by a Noncooperative Mechanism, and Its Activity Is Unaffected by Manipulations at the Predicted Dimer Interface.

Biochemistry 2018 07 4;57(29):4312-4324. Epub 2016 Nov 4.

Department of Biochemistry, Purdue University Center for Cancer Research , Purdue University , West Lafayette , Indiana 47907 , United States.

The catalytic domains of the de novo DNA methyltransferases Dnmt3a-C and Dnmt3b-C are highly homologous. However, their unique biochemical properties could potentially contribute to differences in the substrate preferences or biological functions of these enzymes. Dnmt3a-C forms tetramers through interactions at the dimer interface, which also promote multimerization on DNA and cooperativity. Similar to the case for processive enzymes, cooperativity allows Dnmt3a-C to methylate multiple sites on the same DNA molecule; however, it is unclear whether Dnmt3b-C methylates DNA by a cooperative or processive mechanism. The importance of the tetramer structure and cooperative mechanism is emphasized by the observation that the R882H mutation in the dimer interface of DNMT3A is highly prevalent in acute myeloid leukemia and leads to a substantial loss of its activity. Under conditions that distinguish between cooperativity and processivity, we show that in contrast to that of Dnmt3a-C, the activity of Dnmt3b-C is not cooperative and confirm the processivity of Dnmt3b-C and the full length Dnmt3b enzyme. Whereas the R878H mutation (mouse homologue of R882H) led to the loss of cooperativity of Dnmt3a-C, the activity and processivity of the analogous Dnmt3b-C R829H variant were comparable to those of the wild-type enzyme. Additionally, buffer acidification that attenuates the dimer interface interactions of Dnmt3a-C had no effect on Dnmt3b-C activity. Taken together, these results demonstrate an important mechanistic difference between Dnmt3b and Dnmt3a and suggest that interactions at the dimer interface may play a limited role in regulating Dnmt3b-C activity. These new insights have potential implications for the distinct biological roles of Dnmt3a and Dnmt3b.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acs.biochem.6b00964DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5992102PMC
July 2018

An epigenetic switch regulates de novo DNA methylation at a subset of pluripotency gene enhancers during embryonic stem cell differentiation.

Nucleic Acids Res 2016 09 13;44(16):7605-17. Epub 2016 May 13.

Department of Biochemistry, Purdue University, West Lafayette, IN 47907, USA Purdue University Center for Cancer Research, Purdue University, West Lafayette, IN 47907, USA

Coordinated regulation of gene expression that involves activation of lineage specific genes and repression of pluripotency genes drives differentiation of embryonic stem cells (ESC). For complete repression of pluripotency genes during ESC differentiation, chromatin at their enhancers is silenced by the activity of the Lsd1-Mi2/NuRD complex. The mechanism/s that regulate DNA methylation at these enhancers are largely unknown. Here, we investigated the affect of the Lsd1-Mi2/NuRD complex on the dynamic regulatory switch that induces the local interaction of histone tails with the Dnmt3 ATRX-DNMT3-DNMT3L (ADD) domain, thus promoting DNA methylation at the enhancers of a subset of pluripotency genes. This is supported by previous structural studies showing a specific interaction between Dnmt3-ADD domain with H3K4 unmethylated histone tails that is disrupted by histone H3K4 methylation and histone acetylation. Our data suggest that Dnmt3a activity is triggered by Lsd1-Mi2/NuRD-mediated histone deacetylation and demethylation at these pluripotency gene enhancers when they are inactivated during mouse ESC differentiation. Using Dnmt3 knockout ESCs and the inhibitors of Lsd1 and p300 histone modifying enzymes during differentiation of E14Tg2A and ZHBTc4 ESCs, our study systematically reveals this mechanism and establishes that Dnmt3a is both reader and effector of the epigenetic state at these target sites.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1093/nar/gkw426DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5027477PMC
September 2016