Microsatellite instability induced mutations in DNA repair genes CtIP and MRE11 confer hypersensitivity to poly (ADP-ribose) polymerase inhibitors in myeloid malignancies.

Inactivation of the DNA mismatch repair pathway manifests as microsatellite instability, an accumulation of mutations that drives carcinogenesis. Here, we determined whether microsatellite instability in acute myeloid leukemia and myelodysplastic syndrome correlated with chromosomal instability and poly (ADP-ribose) polymerase (PARP) inhibitor sensitivity through disruption of DNA repair function. Acute myeloid leukemia cell lines (n=12) and primary cell samples (n=18), and bone marrow mononuclear cells from high-risk myelodysplastic syndrome patients (n=63) were profiled for microsatellite instability using fluorescent fragment polymerase chain reaction. PARP inhibitor sensitivity was performed using cell survival, annexin V staining and cell cycle analysis. Homologous recombination was studied using immunocytochemical analysis. SNP karyotyping was used to study chromosomal instability. RNA silencing, Western blotting and gene expression analysis was used to study the functional consequences of mutations. Acute myeloid leukemia cell lines (4 of 12, 33%) and primary samples (2 of 18, 11%) exhibited microsatellite instability with mono-allelic mutations in CtIP and MRE11. These changes were associated with reduced expression of mismatch repair pathway components, MSH2, MSH6 and MLH1. Both microsatellite instability positive primary acute myeloid leukemia samples and cell lines demonstrated a downregulation of homologous recombination DNA repair conferring marked sensitivity to PARP inhibitors. Similarly, bone marrow mononuclear cells from 11 of 56 (20%) patients with de novo high-risk myelodysplastic syndrome exhibited microsatellite instability. Significantly, all 11 patients with microsatellite instability had cytogenetic abnormalities with 4 of them (36%) possessing a mono-allelic microsatellite mutation in CtIP. Furthermore, 50% reduction in CtIP expression by RNA silencing also down-regulated homologous recombination DNA repair responses conferring PARP inhibitor sensitivity, whilst CtIP differentially regulated the expression of homologous recombination modulating RecQ helicases, WRN and BLM. In conclusion, microsatellite instability dependent mutations in DNA repair genes, CtIP and MRE11 are detected in myeloid malignancies conferring hypersensitivity to PARP inhibitors. Microsatellite instability is significantly correlated with chromosomal instability in myeloid malignancies.

IL-17-producing CD4(+) T cells, pro-inflammatory cytokines and apoptosis are increased in low risk myelodysplastic syndrome.

Immunological responses are increasingly recognised as being important in the initiation and progression of myelodysplastic syndrome (MDS). Indeed, autoimmune diseases commonly occur in association with MDS, particularly in subtypes with a low risk of leukaemic transformation. This study showed for the first time that the numbers of CD3(+) CD4(+) IL-17 producing T cells (Th17) were markedly increased in low risk MDS compared with high risk MDS (P < 0.01). An inverse relationship between the numbers of Th17 cells and naturally occurring CD4(+)CD25(high) FoxP3(+) regulatory T cells (Tregs) were also described. The Th17:Tregs ratio was significantly higher in low risk disease (P < 0.005) compared with high risk MDS and was correlated with increased bone marrow (BM) apoptosis (P < 0.01). Tregs from MDS patients suppressed interferon-gamma (IFN-gamma) secretion by effector CD4(+) T cells but had no effect on interleukin (IL)-17 production. In addition, the serum levels of IL-7, IL-12, RANTES and IFN-gamma are significantly elevated in low risk MDS, while inhibitory factors, such as IL-10 and soluble IL-2 receptor, are significantly higher in high risk disease. The 'unfavourable' Th17:Tregs ratio in low risk MDS may explain the higher risk of autoimmunity and the improved response to immune suppression in patients with low risk MDS compared to those with high risk disease.

Urinary protein and essential hypertension in black and in white people.

The objectives of this work were to examine the association between urinary protein and blood pressure and to compare the pattern of urinary protein excretion with essential hypertension in people of European origin (whites) and in people of African or African-Caribbean origin (blacks) living in southwest London, United Kingdom. In the groups as a whole, there were no significant differences in total urinary protein excretion between blacks and whites (geometric means [95% CI]: 94.0 [85.9 to 102.9] mg/24h for the blacks [n=151] and 102.1 [96.1 to 108.4] mg/24h for the whites [n= 219]). There were also no significant differences between blacks and whites in urinary albumin (6.5 [4.9 to 8.5] mg/24h for the blacks [n=97] and 7.1 [5.6 to 9.0] mg/24h for the whites [n=123]). In both groups, those with essential hypertension displayed a significantly raised urinary protein excretion (1.21-fold higher for the blacks and 1.19-fold higher for the whites) and albumin excretion (1.69-fold higher for the blacks and 2.40-fold higher for the whites). Urinary transferrin excretion measured in a subgroup of 67 subjects was also raised in those with essential hypertension (3.22-fold higher in the blacks and 2.76-fold higher in the whites). Examination of urinary proteins by SDS-PAGE did not identify any pattern consistent with a reduction in renal tubular protein reabsorption in those with essential hypertension. These results suggest that the increase in protein excretion in essential hypertension could be due, at least in part, to an increase in glomerular protein ultrafiltration.