Expression of Constitutive Fusion of Ubiquitin to PCNA Restores the Level of Immunoglobulin A/T Mutations During Somatic Hypermutation in the Ramos Cell Line

Somatic hypermutation (SHM) of immunoglobulin (Ig) genes is a B cell specific process required for the generation of specific and high affinity antibodies during the maturation of the immune response against foreign antigens. This process depends on the activity of both activation-induced cytidine deaminase (AID) and several DNA repair factors. AID-dependent SHM creates the full spectrum of mutations in Ig variable (V) regions equally distributed at G/C and A/T bases. In most mammalian cells, deamination of deoxycytidine into uracil during S phase induces targeted G/C mutagenesis using either direct replication of uracils or TLS mediated bypass, however only the machinery of activated B lymphocytes can generate A/T mutagenesis around AID-created uracils. The molecular mechanism behind the latter remains incompletely understood to date. However, the lack of a cellular model that reproduces both G/C and A/T mutation spectra constitutes the major hurdle to elucidating it. The few available B cell lines used thus far to study Ig SHM indeed undergo mainly G/C mutations, that make them inappropriate or of limited use. In this report, we show that in the Ramos cell line that undergoes constitutive G/C-biased SHM in culture, the low rate of A/T mutations is due to an imbalance in the ubiquitination/deubiquitination reaction of PCNA, with the deubiquitination reaction being predominant. The inhibition of the deubiquitinase complex USP1-UAF1 or the expression of constitutive fusion of ubiquitin to PCNA provides the missing clue required for DNA polymerase η recruitment and thereafter the introduction of A/T base pair (bp) mutations during the process of IgV gene diversification. This study reports the establishment of the first modified human B cell line that recapitulates the mechanism of SHM of Ig genes in vitro.

Large deletions in immunoglobulin genes are associated with a sustained absence of DNA Polymerase η

Somatic hypermutation of immunoglobulin genes is a highly mutagenic process that is B cell-specific and occurs during antigen-driven responses leading to antigen specificity and antibody affinity maturation. Mutations at the Ig locus are initiated by Activation-Induced cytidine Deaminase and are equally distributed at G/C and A/T bases. This requires the establishment of error-prone repair pathways involving the activity of several low fidelity DNA polymerases. In the physiological context, the G/C base pair mutations involve multiple error-prone DNA polymerases, while the generation of mutations at A/T base pairs depends exclusively on the activity of DNA polymerase η. Using two large cohorts of individuals with xeroderma pigmentosum variant (XP-V), we report that the pattern of mutations at Ig genes becomes highly enriched with large deletions. This observation is more striking for patients older than 50 years. We propose that the absence of Pol η allows the recruitment of other DNA polymerases that profoundly affect the Ig genomic landscape.

RNase H2, mutated in Aicardi-Goutières syndrome, promotes LINE-1 retrotransposition

Long INterspersed Element class 1 (LINE-1) elements are a type of abundant retrotransposons active in mammalian genomes. An average human genome contains ~100 retrotransposition-competent LINE-1s, whose activity is influenced by the combined action of cellular repressors and activators. TREX1, SAMHD1 and ADAR1 are known LINE-1 repressors and when mutated cause the autoinflammatory disorder Aicardi-Goutières syndrome (AGS). Mutations in RNase H2 are the most common cause of AGS, and its activity was proposed to similarly control LINE-1 retrotransposition. It has therefore been suggested that increased LINE-1 activity may be the cause of aberrant innate immune activation in AGS Here, we establish that, contrary to expectations, RNase H2 is required for efficient LINE-1 retrotransposition. As RNase H1 overexpression partially rescues the defect in RNase H2 null cells, we propose a model in which RNase H2 degrades the LINE-1 RNA after reverse transcription, allowing retrotransposition to be completed. This also explains how LINE-1 elements can retrotranspose efficiently without their own RNase H activity. Our findings appear to be at odds with LINE-1-derived nucleic acids driving autoinflammation in AGS.

Association between psychological distress and cancer type in patients referred to a psycho-oncology service

Psychological distress is common in patients with cancer and psychological well-being is increasingly seen as an important component of cancer care. The aim of this study was to examine the relationship between cancer type and subjective distress. The following data were collected from a database of consecutive psycho-oncology referrals to the Liaison Psychiatry service in Cork University Hospital from 2006 to 2015: demographics, cancer diagnosis, Distress Thermometer (DT) score. 2102 out of 2384 referrals were assessed. Of those assessed, the most common cancer diagnoses were breast (23%, n=486) followed by haematological (21%, n=445). There were significant difference in DT score between the different cancer types, (?2(13)=33.685, p=0.001, Kruskal-Wallis test). When adjusted for age, gender and whether or not the cancer was recently diagnosed, there was no significant association between cancer type and psychological distress. In conclusion, cancer type is not associated with level of distress in cancer.

Immunohistochemical nuclear staining for P53 in nodular scabies

Fifty patients with scabies were included in this study. Clinical, parasitological and histopathological study of all patients was done. P-53 expression was examined, using immunohistochemical techniques. Biopsies of nodular scabies showed atypical changes in the epidermis, the dermis showed dense inflammatory infiltrate. Focal positivity for P-53 have been demonstrated which could favour premalignant changes, and recommend further investigations.

Problems of duodenogastric reflux in Tc-99m Hexa MIBI planar, tomographic and bull's eye display

Tc-99m Hexa MIBI (RP-30) is excreted through hepatobiliary pathways. Myocardial imaging with RP-30 is recommended 45-60 minutes after injection. During this waiting period duodenogastric reflux (DGR) is occasionally seen. Fundal activity due to duodenogastrix reflux presents problems in planar, tomographic, and Bull's eye display. The authors recommend in those cases to give the patient a light meal and wait 15-30 minutes more for the gastric activity to empty in the small intestine before starting myocardial imaging.

Radionuclide findings in arteriovenous fistula between left pulmonary artery and vein

Right-to-left extra cardiac shunts are usually congenital and are rarely due to trauma or complicating thoracic or vascular surgery. A case of a right-to-left cardiac shunt due to an arteriovenous fistula between the left pulmonary artery and the left pulmonary vein is reported. This may be the first report of this abnormality. The etiology is not clear. The case was investigated only by radionuclide procedures because the general condition of the patient was so poor that invasive procedures could not be undertaken.