Chromosome Mis-segregation Generates Cell-Cycle-Arrested Cells with Complex Karyotypes that Are Eliminated by the Immune System.

Aneuploidy, a state of karyotype imbalance, is a hallmark of cancer. Changes in chromosome copy number have been proposed to drive disease by modulating the dosage of cancer driver genes and by promoting cancer genome evolution. Given the potential of cells with abnormal karyotypes to become cancerous, do pathways that limit the prevalence of such cells exist? By investigating the immediate consequences of aneuploidy on cell physiology, we identified mechanisms that eliminate aneuploid cells. We find that chromosome mis-segregation leads to further genomic instability that ultimately causes cell-cycle arrest. We further show that cells with complex karyotypes exhibit features of senescence and produce pro-inflammatory signals that promote their clearance by the immune system. We propose that cells with abnormal karyotypes generate a signal for their own elimination that may serve as a means for cancer cell immunosurveillance.

Clinical variability of family members with the C104R mutation in transmembrane activator and calcium modulator and cyclophilin ligand interactor (TACI).

PURPOSE: Common Variable Immunodeficiency Disorder (CVID) is a complex disorder that predisposes patients to recurrent and severe infections. The C104R mutation in the transmembrane activator and calcium modulator and cyclophilin ligand interactor (TACI) is the most frequent mutation identified in patients with CVID. We carried out a detailed immunological and molecular study in a family with a C104R mutation. METHODS: We have undertaken segregation analysis of a kindred with C104R mutations of the TACI gene. Detailed immunological and molecular investigations were carried out for this kindred and the clinical phenotype was compared to the genotype. RESULTS: Segregation analysis of our kindred showed that inheriting single or double copy of the C104R mutation does not consign an individual to CVID. All heterozygotes in the family were phenotypically different, ranging from asymptomatic to ill-health. A family member with a wild type TACI variant had CVID-related phenotype including IgA deficiency and type 1 diabetes. Interestingly, a family member with the homozygous C104R/C104R variant did not meet the criteria for CVID because he had excellent, albeit unsustained, vaccine responses to T cell dependent and T cell independent vaccine antigens despite profound hypogammaglobulinemia. CONCLUSION: The C104R mutation does not correlate with the clinical phenotypes in this family.

Mitochondrial DNA segregation in hematopoietic lineages does not depend on MHC presentation of mitochondrially encoded peptides.

Mutations in mitochondrial DNA (mtDNA) are associated with a broad spectrum of clinical disorders. The segregation pattern of pathogenic mtDNAs is an important determinant of both the onset and the severity of the disease phenotype, but the mechanisms controlling mtDNA segregation remain poorly understood. To investigate this, we previously generated heteroplasmic mice containing two different mtDNA haplotypes and showed that BALB/c mtDNA was invariably selected over NZB mtDNA in blood and spleen. Here, we have characterized this process in hematopoietic tissues and tested whether it involves the presentation of mtDNA-encoded peptides by MHC class Ib molecules. Selection against NZB mtDNA was widespread across different hematopoietic cell lineages and proportional to heteroplasmy levels. Backcrossing heteroplasmic mice with CAST/Ei, a strain in which the MHC class Ib molecule H2-M3 is silent, completely abolished selection against NZB mtDNA in the spleen. To test whether this effect depended on an intact immune system, we generated heteroplasmic mice missing functional copies of Tap1, beta2m or Rag1 to impair presentation or recognition of mtDNA-encoded peptides. The kinetics of selection against NZB mtDNA were unaltered in these mice compared with their wild-type littermates. We conclude that mtDNA selection in hematopoietic tissues is not based on an immune mechanism, but likely involves metabolic signaling.

The identification of a novel T cell activation state controlled by a diabetogenic gene.

The cyclin-dependent kinase inhibitor p27(kip) regulates the cell cycle at the G(1)-S phase restriction point. S phase entry and cell cycle commitment in peripheral T cells requires p27(kip) degradation, normally initiated by the receipt of costimulatory signals such as those provided by B7.1 or IL-2. We have previously reported that T cells from BioBreeding (BB)-diabetes-prone (DP) rats exhibit decreased costimulatory requirements for activation and cell cycle entry. In the present study, we find that peripheral T cell subsets from BB-DP rats demonstrate activation-like characteristics, including significantly reduced levels of p27(kip) as well as increased levels of proliferating cell nuclear Ag (PCNA). Since our previous studies have established that expression of extracellular activation markers are relatively low in unmanipulated peripheral BB-DP T cells; this p27(low) PCNA(high) phenotype represents a novel activation state. Analyses of T cell subsets from congenic rats demonstrate that this phenotype segregates with the lyp diabetogenic locus and that the p27(low) PCNA(high) phenotype is T cell specific. This p27(low) PCNA(high) phenotype is not seen in medullary thymocytes, but appears abruptly in the recent thymic emigrant population, suggesting that the lyp locus does not act directly on cell cycle regulators but rather alters the interaction between T cells and the peripheral environment. These results provide a biochemical basis for costimulation-independent activation and suggest a mechanism whereby a diabetes susceptibility gene contributes to disease development.

Parental segregation of autoimmunity in patients with Turner's syndrome: preferential paternal transmission?

The prevalence of autoantibodies has been reported to be increased in both patients with Turner's syndrome and their parents. We evaluated organ-specific and non-organ-specific autoantibodies in 95 patients, ranging in age from infancy to adulthood, and in most of their parents, in order to determine the characteristics of autoimmune disorders in these families and to relate it to the genetic markers usually involved in autoimmunity (HLA, GM and KM genes). A statistically significant difference was observed between Turner patients and controls in the frequencies of organ-specific autoantibodies, in particular thyroid microsomal antibodies and thyroglobulin antibodies; however, the presence of autoantibodies was not associated with overt diseases in most cases. No significant difference was found between parents and controls. A study of the inheritance of the autoimmunity showed that transmission was preferentially paternal, since Turner patients had more chance of presenting autoantibodies when their fathers had autoantibodies rather than their mothers. A positive association was found between the presence of auto-antibodies and HLA-DR7;DQ2 and HLA-DR7;DQ9 haplotypes in Turner patients and fathers. No significant association was found between GM and KM allotype frequencies in Turner patients and their parents and the presence of autoantibodies. No epistatic interaction was demonstrated between HLA and GM or KM genes. Familial segregation was studied and a preferentially paternal transmission of HLA-DR7-carrying haplotypes and possibly also of the KM (1) allotype with autoimmunity was observed.