6 research outputs found
Mechanistic insights into p53âregulated cytotoxicity of combined entinostat and irinotecan against colorectal cancer cells
Lateâstage colorectal cancer (CRC) is still a clinically challenging problem. The activity of the tumor suppressor p53 is regulated via postâtranslational modifications (PTMs). While the relevance of p53 Câterminal acetylation for transcriptional regulation is well defined, it is unknown whether this PTM controls mitochondrially mediated apoptosis directly. We used wildâtype p53 or p53ânegative human CRC cells, cells with acetylationâdefective p53, transformation assays, CRC organoids, and xenograft mouse models to assess how p53 acetylation determines cellular stress responses. The topoisomeraseâ1 inhibitor irinotecan induces acetylation of several lysine residues within p53. Inhibition of histone deacetylases (HDACs) with the class I HDAC inhibitor entinostat synergistically triggers mitochondrial damage and apoptosis in irinotecanâtreated p53âpositive CRC cells. This specifically relies on the Câterminal acetylation of p53 by CREBâbinding protein/p300 and the presence of Câterminally acetylated p53 in complex with the proapoptotic BCL2 antagonist/killer protein. This control of Câterminal acetylation by HDACs can mechanistically explain why combinations of irinotecan and entinostat represent clinically tractable agents for the therapy of p53âproficient CRC
Kinetics of poly(ADP-ribosyl)ation, but not PARP1 itself, determines the cell fate in response to DNA damage in vitro and in vivo
One of the fastest cellular responses to genotoxic stress is the formation of poly(ADP-ribose) polymers (PAR) by poly(ADP-ribose)polymerase 1 (PARP1, or ARTD1). PARP1 and its enzymatic product PAR regulate diverse biological processes, such as DNA repair, chromatin remodeling, transcription and cell death. However, the inter-dependent function of the PARP1 protein and its enzymatic activity clouds the mechanism underlying the biological response. We generated a PARP1 knock-in mouse model carrying a point mutation in the catalytic domain of PARP1 (D993A), which impairs the kinetics of the PARP1 activity and the PAR chain complexity in vitro and in vivo, designated as hypo-PARylation. PARP1D993A/D993A mice and cells are viable and show no obvious abnormalities. Despite a mild defect in base excision repair (BER), this hypo-PARylation compromises the DNA damage response during DNA replication, leading to cell death or senescence. Strikingly, PARP1D993A/D993A mice are hypersensitive to alkylation in vivo, phenocopying the phenotype of PARP1 knockout mice. Our study thus unravels a novel regulatory mechanism, which could not be revealed by classical loss-of-function studies, on how PAR homeostasis, but not the PARP1 protein, protects cells and organisms from acute DNA damage.publishe
Evolutionary epidemiology of Neisseria meningitidis strains in Belarus compared to other European countries
Meningococcal infections are major causes of death in children
globally. In Belarus, the incidence of cases and fatality rate of meningococcal infec-
tions are low and comparable to the levels in other European countries.
Aim.
In the
present study, the molecular and epidemiological traits of
Neisseria meningitidis
strains circulating in Belarus were characterized and compared to isolates from other
European countries.
Materials and Methods.
Twenty
N. meningitidis
strains isolated
from patients (n = 13) and healthy contacts (n = 7) during 2006â2012 in Belarus were
selected for multilocus sequence typing (MLST), genosubtyping and FetA typing. The
STs of the Belarusian strains were phylogenetically compared to the STs of 110 se
-
lected strains from 22 other European countries.
Results.
Overall, eleven different
genosubtypes were observed, there were seven variants of variable region of the
fetA
gene detected. The majority of the STs (95%) found in Belarus were novel and all
those were submitted to the Neisseria MLST database for assignment. Several newly
discovered alleles of
fumC
(allele 451) and
gdh
(allele 560 and 621) appeared to be de
-
scendants of alleles which are widespread in Europe, and single
aroE
alleles (602 and
603) occurred as a result of separate evolution.
Conclusions. N. meningitidis
strains
circulating in Belarus are heterogeneous and include sequence types, possibly, locally
evolved in Belarus as well as representatives of widespread European hyperinvasive
clonal complexes
Kinetics of poly(ADP-ribosyl)ation, but not PARP1 itself, determines the cell fate in response to DNA damage in vitro and in vivo
One of the fastest cellular responses to genotoxic stress is the formation of poly(ADP-ribose) polymers (PAR) by poly(ADP-ribose)polymerase 1 (PARP1, or ARTD1). PARP1 and its enzymatic product PAR regulate diverse biological processes, such as DNA repair, chromatin remodeling, transcription and cell death. However, the inter-dependent function of the PARP1 protein and its enzymatic activity clouds the mechanism underlying the biological response. We generated a PARP1 knock-in mouse model carrying a point mutation in the catalytic domain of PARP1 (D993A), which impairs the kinetics of the PARP1 activity and the PAR chain complexity in vitro and in vivo, designated as hypo-PARylation. PARP1D993A/D993A mice and cells are viable and show no obvious abnormalities. Despite a mild defect in base excision repair (BER), this hypo-PARylation compromises the DNA damage response during DNA replication, leading to cell death or senescence. Strikingly, PARP1D993A/D993A mice are hypersensitive to alkylation in vivo, phenocopying the phenotype of PARP1 knockout mice. Our study thus unravels a novel regulatory mechanism, which could not be revealed by classical loss-of-function studies, on how PAR homeostasis, but not the PARP1 protein, protects cells and organisms from acute DNA damage