Sporadic immunogenic tumours avoid destruction by inducing T-cell tolerance

The recognition and elimination of tumours by T cells, a process termed cancer immunosurveillance, is effective against certain virus-associated cancers. Spontaneous tumours often induce a specific immune response and are therefore also immunogenic. However, it is not clear whether they can be controlled by T cells. The immunosurveillance hypothesis postulates that tumours, if they eventually grow, escaped T-cell recognition by losing immunogenicity. Here we show, by generating a mouse model of sporadic cancer based on rare spontaneous activation of a dormant oncogene, that immunogenic tumours do not escape their recognition but induce tolerance. In this model, tumours derive from single cells and express a tumour-specific transplantation rejection antigen. Whereas vaccinated mice remain tumour-free throughout their lifetime, naive mice always develop a progressively growing tumour. We also show that despite specific recognition by T cells, the tumours do not lose their intrinsic immunogenicity and are rejected after transplantation in T-cell-competent recipients. Furthermore, in the primary host tumour-induced tolerance is associated with the expansion of non-functional T cells. Together, our data argue against immunosurveillance of spontaneous cancer.     

Complex inheritance of familial hypercholanemia with associated mutations in TJP2 and BAAT

Familial hypercholanemia (FHC) is characterized by elevated serum bile acid concentrations, itching, and fat malabsorption. We show here that FHC in Amish individuals is associated with mutations in tight junction protein 2 (encoded by TJP2, also known as ZO-2) and bile acid Coenzyme A: amino acid N-acyltransferase (encoded by BAAT). The mutation of TJP2, which occurs in the first PDZ domain, reduces domain stability and ligand binding in vitro. We noted a morphological change in hepatic tight junctions. The mutation of BAAT, a bile acid-conjugating enzyme, abrogates enzyme activity; serum of individuals homozygous with respect to this mutation contains only unconjugated bile acids. Mutations in both TJP2 and BAAT may disrupt bile acid transport and circulation. Inheritance seems to be oligogenic, with genotype at BAAT modifying penetrance in individuals homozygous with respect to the mutation in TJP2.     

Mutations in PCSK9 cause autosomal dominant hypercholesterolemia

Autosomal dominant hypercholesterolemia (ADH; OMIM144400), a risk factor for coronary heart disease, is characterized by an increase in low-density lipoprotein cholesterol levels that is associated with mutations in the genes LDLR (encoding low-density lipoprotein receptor) or APOB (encoding apolipoprotein B). We mapped a third locus associated with ADH, HCHOLA3 at 1p32, and now report two mutations in the gene PCSK9 (encoding proprotein convertase subtilisin/kexin type 9) that cause ADH. PCSK9 encodes NARC-1 (neural apoptosis regulated convertase), a newly identified human subtilase that is highly expressed in the liver and contributes to cholesterol homeostasis.     

RecBCD enzyme is a DNA helicase with fast and slow motors of opposite polarity

Helicases are molecular motors that move along and unwind double-stranded nucleic acids. RecBCD enzyme is a complex helicase and nuclease, essential for the major pathway of homologous recombination and DNA repair in Escherichia coli. It has sets of helicase motifs in both RecB and RecD, two of its three subunits. This rapid, highly processive enzyme unwinds DNA in an unusual manner: the 5'-ended strand forms a long single-stranded tail, whereas the 3'-ended strand forms an ever-growing single-stranded loop and short single-stranded tail. Here we show by electron microscopy of individual molecules that RecD is a fast helicase acting on the 5'-ended strand and RecB is a slow helicase acting on the 3'-ended strand on which the single-stranded loop accumulates. Mutational inactivation of the helicase domain in RecB or in RecD, or removal of the RecD subunit, altered the rates of unwinding or the types of structure produced, or both. This dual-helicase mechanism explains how the looped recombination intermediates are generated and may serve as a general model for highly processive travelling machines with two active motors, such as other helicases and kinesins.