Biology subjects

Mahmoud, S. A.

Publications and source records attributed to Mahmoud, S. A..

3 recordsLinked to original sources

bioRxiv2024

Runx3 Acts as Homodimeric Chromatin Binding Factor Regulating Heterochromatin-Mediated Cancerous Phenotype

The recent paradoxical dual citizenships of Runt-related transcription factor 3 (Runx3) in tumorigenesis remains poorly characterized. Here, we report the oncogenic capacity of Runx3 as chromatin modulator in metastatic gastric cancer model. Runx3 exists as homodimer and binds cooperatively to modified nucleosomes. Additionally, we detected a synergistic functional enhancement of octamer transfer, nucleosome sliding and stochiometric integrity of SWI/SNF by Runx3. We found that Runx3 depletion increased nucleosomes occupancy and promoted chromatin silencing by heterochromatin condensation and HP1 oligomerization. ATAC-seq analysis revealed differential accessibility per chromosome due to Runx3 null expression with dysregulation of multiple inflammatory response and DNA repair pathways. Mechanistically, these modulations resulted in aberrant DNA damage repair response, which is rescued by RUNX3 overexpression. These findings reveal a new paradigm in Runx3 biology as dynamic chromatin regulatory element vital for the maintenances of cancerous phenotype. SignificanceTo the best of our knowledge, the present study is the first to explore the role of Runx3 as homodimeic chromatin binding factor and establishes its oncogenic-function as modulator of heterochromatin de-condensation and SWI/SNF chromatin remodeling activities. These emerging features of Runx3 at the epigenetic level imply a promising direction to screen for anti-Runx3 epigenetic drugs "Epi-drugs" in search of novel gastric cancer treatment.

cancer biology↗

bioRxiv2021

Plasticity in AAA+ proteases reveals ATP-dependent substrate specificity principles

In bacteria, AAA+ proteases such as Lon and ClpXP degrade substrates with exquisite specificity. These machines capture the energy of ATP hydrolysis to power unfolding and degradation of target substrates. Here, we show that a mutation in the ATP binding site of ClpX shifts protease specificity to promote degradation of normally Lon-restricted substrates. However, this ClpX mutant is worse at degrading ClpXP targets, suggesting an optimal balance in substrate preference for a given protease that is surprisingly easy to alter. In vitro, wildtype ClpXP also degrades Lon-restricted substrates more readily when ATP levels are reduced, similar to the shifted specificity of mutant ClpXP, which has altered ATP hydrolysis kinetics. Based on these results, we suggest that rates of ATP hydrolysis not only power substrate unfolding and degradation, but also tune protease specificity. We consider various models for this effect based on emerging structures of AAA+ machines showing conformationally distinct states. O_FIG O_LINKSMALLFIG WIDTH=197 HEIGHT=200 SRC="FIGDIR/small/456811v2_ufig1.gif" ALT="Figure 1"> View larger version (67K): org.highwire.dtl.DTLVardef@1b72081org.highwire.dtl.DTLVardef@1b713c7org.highwire.dtl.DTLVardef@73a92aorg.highwire.dtl.DTLVardef@167422d_HPS_FORMAT_FIGEXP M_FIG Graphical Abstract C_FIG eTOCAAA+ proteases, such as Lon and ClpXP, select distinct targets for degradation to maintain proteostasis. Mahmoud et al. show that ATP hydrolysis can tune substrate specificity of ClpX, allowing ClpX to degrade Lon-restricted substrates under limiting ATP conditions or in the presence of a ClpX mutant. HighlightsO_LIA Walker B mutation of the AAA+ protease ClpX alters substrate specificity C_LIO_LIClpX mutant degrades new substrates but degrades canonical substrates less well C_LIO_LIDecreasing ATP levels enhances ClpXP mediated degradation of some classes of substrates C_LIO_LIATP-induced changes in conformational states accompany alterations in ClpX specificity C_LI

molecular biology↗

bioRxiv2020

Degradation of Lon in Caulobacter crescentus

Protein degradation is an essential process in all organisms. This process is irreversible and energetically costly; therefore, protein destruction must be tightly controlled. While environmental stresses often lead to upregulation of proteases at the transcriptional level, little is known about post-translational control of these critical machines. In this study we show that in Caulobacter crescentus levels of the Lon protease are controlled through proteolysis. Lon turnover requires active Lon and ClpAP proteases. We show that specific determinants dictate Lon stability with a key carboxy-terminal histidine residue driving recognition. Expression of stabilized Lon variants results in toxic levels of protease that deplete normal Lon substrates such as the replication initiator DnaA to lethally low levels. Taken together, this work demonstrates a feedback mechanism in which ClpAP and Lon collaborate to tune Lon proteolytic capacity for the cell. ImportanceProteases are essential, but unrestrained activity can also kill cells by degrading essential proteins. The quality control protease Lon must degrade many misfolded and native substrates. We show that Lon is itself controlled through proteolysis and that bypassing this control results in toxic consequences for the cell.

microbiology↗