Inactive Parp2 causes Tp53-dependent lethal anemia by blocking replication-associated nick ligation in erythroblasts.

PARP1&2 enzymatic inhibitors (PARPi) are promising cancer treatments. But recently, their use has been hindered by unexplained severe anemia and treatment-related leukemia. In addition to enzymatic inhibition, PARPi also trap PARP1&2 at DNA lesions. Here, we report that unlike Parp2 -/- mice, which develop normally, mice expressing catalytically-inactive Parp2 (E534A, Parp2 EA/EA ) succumb to Tp53- and Chk2 -dependent erythropoietic failure in utero , mirroring Lig1 -/- mice. While DNA damage mainly activates PARP1, we demonstrate that DNA replication activates PARP2 robustly. PARP2 is selectively recruited and activated by 5'-phosphorylated nicks (5'p-nicks) between Okazaki fragments, typically resolved by Lig1. Inactive PARP2, but not its active form or absence, impedes Lig1- and Lig3-mediated ligation, causing dose-dependent replication fork collapse, particularly harmful to erythroblasts with ultra-fast forks. This PARylation-dependent structural function of PARP2 at 5'p-nicks explains the detrimental effects of PARP2 inhibition on erythropoiesis, revealing the mechanism behind the PARPi-induced anemia and leukemia, especially those with TP53/CHK2 loss. Significance: This work shows that the hematological toxicities associated with PARP inhibitors stem not from impaired PARP1 or PARP2 enzymatic activity but rather from the presence of inactive PARP2 protein. Mechanistically, these toxicities reflect a unique role of PARP2 at 5'-phosphorylated DNA nicks during DNA replication in erythroblasts.

Mammalian DNA ligases; roles in maintaining genome integrity.

The joining of breaks in the DNA phosphodiester backbone is essential for genome integrity. Breaks are generated during normal processes such as DNA replication, cytosine demethylation during differentiation, gene rearrangement in the immune system and germ cell development. In addition, they are generated either directly by a DNA damaging agent or indirectly due to damage excision during repair. Breaks are joined by a DNA ligase that catalyzes phosphodiester bond formation at DNA nicks with 3' hydroxyl and 5' phosphate termini. Three human genes encode ATP-dependent DNA ligases. These enzymes have a conserved catalytic core consisting of three subdomains that encircle nicked duplex DNA during ligation. The DNA ligases are targeted to different nuclear DNA transactions by specific protein-protein interactions. Both DNA ligase IIIα and DNA ligase IV form stable complexes with DNA repair proteins, XRCC1 and XRCC4, respectively. There is functional redundancy between DNA ligase I and DNA ligase IIIα in DNA replication, excision repair and single-strand break repair. Although DNA ligase IV is a core component of the major double-strand break repair pathway, non-homologous end joining, the other enzymes participate in minor, alternative double-strand break repair pathways. In contrast to the nucleus, only DNA ligase IIIα is present in mitochondria and is essential for maintaining the mitochondrial genome. Human immunodeficiency syndromes caused by mutations in either LIG1 or LIG4 have been described. Preclinical studies with DNA ligase inhibitors have identified potentially targetable abnormalities in cancer cells and evidence that DNA ligases are potential targets for cancer therapy.

Unchanged PCNA and DNMT1 dynamics during replication in DNA ligase I-deficient cells but abnormal chromatin levels of non-replicative histone H1.

DNA ligase I (LigI), the predominant enzyme that joins Okazaki fragments, interacts with PCNA and Pol δ. LigI also interacts with UHRF1, linking Okazaki fragment joining with DNA maintenance methylation. Okazaki fragments can also be joined by a relatively poorly characterized DNA ligase IIIα (LigIIIα)-dependent backup pathway. Here we examined the effect of LigI-deficiency on proteins at the replication fork. Notably, LigI-deficiency did not alter the kinetics of association of the PCNA clamp, the leading strand polymerase Pol ε, DNA maintenance methylation proteins and core histones with newly synthesized DNA. While the absence of major changes in replication and methylation proteins is consistent with the similar proliferation rate and DNA methylation levels of the LIG1 null cells compared with the parental cells, the increased levels of LigIIIα/XRCC1 and Pol δ at the replication fork and in bulk chromatin indicate that there are subtle replication defects in the absence of LigI. Interestingly, the non-replicative histone H1 variant, H1.0, is enriched in the chromatin of LigI-deficient mouse CH12F3 and human 46BR.1G1 cells. This alteration was not corrected by expression of wild type LigI, suggesting that it is a relatively stable epigenetic change that may contribute to the immunodeficiencies linked with inherited LigI-deficiency syndrome.

Non-traumatic splenic rupture and pancreatic pseudocyst as a complication of pancreatitis: A case report.

Nontraumatic splenic rupture is a rare pancreatitis complication. We present a 61-year-old chronic alcoholic male with acute on chronic pancreatitis, which progressed to pseudocyst, splenic vein thrombosis, splenic rupture, and eventually hemoperitoneum. Later, the patient required an emergency laparotomy and splenectomy. Early detection and treatment of pancreatitis and pseudocyst can help prevent a rare but potentially fatal complication like an acute rupture.

Multiple intracranial hydatid cysts in posterior fossa in an adult-A case report.

Hydatid cyst is an uncommon parasitic disease caused by larval stages of Echinococcus granulosus. The liver is the most frequently affected organ followed by the lungs and the spleen. Intracranial hydatid cysts are uncommon and occur mostly in supratentorial region. It can present with nonspecific symptoms and can be difficult to diagnose, thus regardless of unusual clinical presentation and unusual location of cystic lesion in brain, it is crucial to keep hydatid cyst as one of the differentials. We describe a case of a 28-year-old male who presented with headache, vomiting and cerebellar signs. MRI showed multiple cystic lesions in posterior fossa with asymmetrically dilated posterior horn of left lateral ventricle. Biopsy from one of the cystic lesions from posterior fossa was performed which confirmed the diagnosis of hydatid cyst. Patient was started on Albendazole and subsequently planned for surgery.

Dyke-Davidoff-Masson syndrome: A rare case of hemiatrophy of brain-Case report from Nepal.

Dyke-Davidoff-Masson syndrome (DDMS) is a rare neurological disorder that results from brain injury during intrauterine or early years of life. Prominent cortical sulci, dilated lateral ventricles, cerebral hemiatrophy, hyperpneumatization of the sinus, and compensatory hypertrophy of the skull are the characteristic findings. We describe a female patient who presented with a history of seizure, right-sided body weakness, and neuroimaging features of left cerebral hemiatrophy, dilatation of left lateral ventricle, left frontal sinus hyperpneumatization, asymmetric calvarial thickening, and elevation of the petrous ridge.

Role of diagnostic imaging in Rasmussen's encephalitis - A case report from Nepal.

Rasmussen's encephalitis (RE) is a relatively rare chronic inflammatory neurological disease that usually only affects one hemisphere of the brain. It primarily affects children under the age of 10, although it can also affect teens and adults, causing drug-resistant seizures, progressive hemiparesis, and dementia. RE presents as a challenging diagnosis with MRI as the cornerstone of the evaluation and nuclear imaging as a complementary tool. We'd like to present a case of a 12-year-old girl who was diagnosed with RE after an MRI. In this study, we examine the diagnostic criteria, differential diagnoses, and issues that underpin the diagnostic challenge in great detail.

Deep venous sinus thrombosis with right thalamic infarction in a young patient after COVID-19 vaccination.

Cerebral venous thrombosis is a rare illness, it compromises 0.5% of cases of cerebrovascular diseases globally. The condition can be treated if discovered and treated properly and quickly. With many known risk factors and in recent times with invent of the COVID-19 vaccine, there have been reported incidences of vaccination being implicated in cerebral venous sinus thrombosis. We report an unusual case of an adolescent female with imaging findings of deep cerebral venous sinus thrombosis and right thalamic infarction after recent vaccination against COVID-19. Laboratory results revealed microcytic hypochromic anemia. Further imaging was done which included a non-contrast CT head, magnetic resonance imaging, and magnetic resonance venography leading to a diagnosis of thrombosis of deep venous (galenic) system with vasogenic edema in bilateral thalami and left caudate nucleus with areas of infarction in the right thalamus. She was treated with subcutaneous low molecular weight heparin (Enoxaparin) and discharged on the third day under oral dabigatran and oral iron.

Human DNA ligases in replication and repair.

To ensure genome integrity, the joining of breaks in the phosphodiester backbone of duplex DNA is required during DNA replication and to complete the repair of almost all types of DNA damage. In human cells, this task is accomplished by DNA ligases encoded by three genes, LIG1, LIG3 and LIG4. Mutations in LIG1 and LIG4 have been identified as the causative factor in two inherited immunodeficiency syndromes. Moreover, there is emerging evidence that DNA ligases may be good targets for the development of novel anti-cancer agents. In this graphical review, we provide an overview of the roles of the DNA ligases encoded by the three human LIG genes in DNA replication and repair.

Altered DNA ligase activity in human disease.

The joining of interruptions in the phosphodiester backbone of DNA is critical to maintain genome stability. These breaks, which are generated as part of normal DNA transactions, such as DNA replication, V(D)J recombination and meiotic recombination as well as directly by DNA damage or due to DNA damage removal, are ultimately sealed by one of three human DNA ligases. DNA ligases I, III and IV each function in the nucleus whereas DNA ligase III is the sole enzyme in mitochondria. While the identification of specific protein partners and the phenotypes caused either by genetic or chemical inactivation have provided insights into the cellular functions of the DNA ligases and evidence for significant functional overlap in nuclear DNA replication and repair, different results have been obtained with mouse and human cells, indicating species-specific differences in the relative contributions of the DNA ligases. Inherited mutations in the human LIG1 and LIG4 genes that result in the generation of polypeptides with partial activity have been identified as the causative factors in rare DNA ligase deficiency syndromes that share a common clinical symptom, immunodeficiency. In the case of DNA ligase IV, the immunodeficiency is due to a defect in V(D)J recombination whereas the cause of the immunodeficiency due to DNA ligase I deficiency is not known. Overexpression of each of the DNA ligases has been observed in cancers. For DNA ligase I, this reflects increased proliferation. Elevated levels of DNA ligase III indicate an increased dependence on an alternative non-homologous end-joining pathway for the repair of DNA double-strand breaks whereas elevated level of DNA ligase IV confer radioresistance due to increased repair of DNA double-strand breaks by the major non-homologous end-joining pathway. Efforts to determine the potential of DNA ligase inhibitors as cancer therapeutics are on-going in preclinical cancer models.

Patient Satisfaction with Nursing Care in Five Major Departments in a Tertiary Care Centre.

INTRODUCTION: Patient satisfaction is an important component of quality nursing care and is often determined by the nursing care in any health institution. The aim of the study is to find the presence of satisfaction among in-ward patients of five major wards at a tertiary care hospital regarding the quality of care provided by nursing staff. METHODS: A descriptive cross-sectional study was conducted among 105 patients of Patan Hospital from 3rd July to 3rd August, 2015 after obtaining ethical clearance from Institutional Review Committee. Sample size was calculated and stratified random sampling was done. Data was collected in Microsoft Excel and analyzed in Sta 13.0. Point estimate at 95% Confidence Interval was calculated and frequency and percentage was calculated for binary data. Subgroup analysis was done on the basis of demographic variables. RESULTS: Among 105 patients, 99 (94.3%) [94.93-95.07 at 95%CI] were satisfied with the nursing care provided at a tertiary care center in Nepal. Among them, 60 (60.6%) were females and 39 (39.4%) were males. Age of the patients ranged from 1 year to 85 years. The length of the stay in the hospital ranged from 2 to 17 days (mean = 5.6 days). CONCLUSIONS: Most of the patients were satisfied with the nursing care provided in a tertiary care centre. Routine nursing care surveys and immediate feedbacks would keep the authorities updated and deliver good health care.