Primary cilium-dependent and -independent Hedgehog signaling inhibits p16(INK4A).

In a genome-wide siRNA analysis of p16(INK4a) (p16) modulators, we identify the Hedgehog (Hh) pathway component SUFU and formally demonstrate that Hh signaling promotes mitogenesis by suppression of p16. A fragment of the Hh-responsive GLI2 transcription factor directly binds and inhibits the p16 promoter and senescence is associated with the loss of nuclear GLI2. Hh components partially reside in the primary cilium (PC), and the small fraction of cells in mass culture that elaborate a PC have the lowest expression of p16. Suppression of p16 is effected by both PC-dependent and -independent routes, and ablation of p16 renders cells insensitive to an Hh inhibitor and increases PC formation. These results directly link a well-established developmental mitogenic pathway with a key tumor suppressor and contribute to the molecular understanding of replicative senescence, Hh-mediated oncogenesis, and potentially the role of p16 in aging.

A whole genome screen for HIV restriction factors.

BACKGROUND: Upon cellular entry retroviruses must avoid innate restriction factors produced by the host cell. For human immunodeficiency virus (HIV) human restriction factors, APOBEC3 (apolipoprotein-B-mRNA-editing-enzyme), p21 and tetherin are well characterised. RESULTS: To identify intrinsic resistance factors to HIV-1 replication we screened 19,121 human genes and identified 114 factors with significant inhibition of infection. Those with a known function are involved in a broad spectrum of cellular processes including receptor signalling, vesicle trafficking, transcription, apoptosis, cross-nuclear membrane transport, meiosis, DNA damage repair, ubiquitination and RNA processing. We focused on the PAF1 complex which has been previously implicated in gene transcription, cell cycle control and mRNA surveillance. Knockdown of all members of the PAF1 family of proteins enhanced HIV-1 reverse transcription and integration of provirus. Over-expression of PAF1 in host cells renders them refractory to HIV-1. Simian Immunodeficiency Viruses and HIV-2 are also restricted in PAF1 expressing cells. PAF1 is expressed in primary monocytes, macrophages and T-lymphocytes and we demonstrate strong activity in MonoMac1, a monocyte cell line. CONCLUSIONS: We propose that the PAF1c establishes an anti-viral state to prevent infection by incoming retroviruses. This previously unrecognised mechanism of restriction could have implications for invasion of cells by any pathogen.

A 3'-untranslated region polymorphism in the TBX21 gene encoding T-bet is a risk factor for genital herpes simplex virus type 2 infection in humans.

It was recently shown that the transcription factor T-bet is crucial for adequate innate and acquired immune responses to genital herpes simplex virus type 2 (HSV-2) infection in mice. To test the possible genetic influence of variations in the TBX21 gene encoding T-bet on susceptibility to infection, this study evaluated the frequencies of five different single-nucleotide polymorphisms (SNPs) in the human TBX21 gene in 159 HSV-2-infected individuals and compared them with those in 186 healthy HSV-2-seronegative controls. The data showed that one variation (rs17244587) in the 3'-untranslated region of TBX21 was strongly associated with the incidence of genital HSV-2 infection. The frequency of the A allele at this position was 0.19 in the group of HSV-2-infected individuals compared with 0.05 in the group of uninfected controls (P=9.3x10(-8)). Furthermore, a homozygous AA genotype was found only among HSV-2-infected individuals and not in seronegative controls. These results indicate that the host genetic background may affect susceptibility to HSV-2 infection in humans, with TBX21 as a strong candidate gene.