The BRCA2-MEILB2-BRME1 complex governs meiotic recombination and impairs the mitotic BRCA2-RAD51 function in cancer cells

Breast cancer susceptibility gene II (BRCA2) is central in homologous recombination (HR). In meiosis, BRCA2 binds to MEILB2 to localize to DNA double-strand breaks (DSBs). Here, we identify BRCA2 and MEILB2-associating protein 1 (BRME1), which functions as a stabilizer of MEILB2 by binding to an α-helical N-terminus of MEILB2 and preventing MEILB2 self-association. BRCA2 binds to the C-terminus of MEILB2, resulting in the formation of the BRCA2-MEILB2-BRME1 ternary complex. In Brme1 knockout (Brme1-/-) mice, the BRCA2-MEILB2 complex is destabilized, leading to defects in DSB repair, homolog synapsis, and crossover formation. Persistent DSBs in Brme1-/- reactivate the somatic-like DNA-damage response, which repairs DSBs but cannot complement the crossover formation defects. Further, MEILB2-BRME1 is activated in many human cancers, and somatically expressed MEILB2-BRME1 impairs mitotic HR. Thus, the meiotic BRCA2 complex is central in meiotic HR, and its misregulation is implicated in cancer development.

Interactions between monomeric CCTδ and p150Glued: A novel function for CCTδ at the cell periphery distinct from the protein folding activity of the molecular chaperone CCT

Chaperonin containing tailless complex polypeptide 1 (CCT) is a molecular chaperone consisting of eight distinct protein subunits, that when oligomeric is essential for the folding of newly synthesized tubulin and actin. In addition to folding, CCT activity includes functions of individual subunits in their monomeric form. For example, when CCTδ monomer levels are increased in cultured mammalian cells, numerous cell surface protrusions are formed from retraction fibres, indicating that an underlying function for the CCTδ monomer exists. Here, using a yeast two-hybrid screen we identify the dynactin complex component p150^Glued as a binding partner for CCTδ and show by siRNA depletion that this interaction is required for the formation of CCTδ-induced cell surface protrusions. Intact microtubules are necessary for the formation of the protrusions, consistent with microtubule minus end transport driving the retraction fibre formation and depletion of either p150^Glued or the dynactin complex-associated transmembrane protein dynAP prevents the previously observed localization of GFP-CCTδ to the plasma membrane. Wound healing assays reveal that CCTδ monomer levels influence directional cell migration and together our observations demonstrate that in addition to the folding activity of CCT in its oligomer form, a monomeric subunit is associated with events that involve the assembled cytoskeleton.

Common haplotypes in CD209 promoter and susceptibility to HIV-1 infection in intravenous drug users

INTRODUCTION

CD209 is a receptor expressed in the dendritic cells involved in recognition of oligosaccharides present in several pathogens with a relevant impact on human health. SNPs located in the promoter region have been associated with HIV-1 susceptibility, although this finding has not been replicated in other populations. The objective of this study is to evaluate the association of CD209 promoter haplotypes with risk of HIV-1 infection in a cohort of Spanish male intravenous drug users (IDU) infected with hepatitis C virus (HCV) and to characterize the phenotypic effects of the associated variants.

METHODS

We genotyped 4 SNPs of CD209 promoter in 295 HCV males exposed to HIV-1 infection by IDU, 165 HIV-1-infected and 130 exposed uninfected (EUI) and 142 healthy controls (HC). We have cloned the promoter variants in a reporter vector and evaluated the promoter activities in a cell culture model. CD209 mRNAs were measured in PBMC.

RESULTS

Single-marker analysis revealed no significant allelic association with the risk of HIV-1 infection by parenteral route. Nevertheless, one haplotype was significantly overrepresented in EUI compared with HIV-1 positive patients and was associated with HIV-1 status (P=0.0008; OR: 0.43). Functional experiments suggested that the protective haplotype displayed lower transcriptional activity in vitro (P<0.05) and this was correlated with lower CD209 mRNA expression in PBMC (P=0.014).

CONCLUSIONS

This study suggests that the promoter haplotypes of CD209 influence the risk of HIV-1 acquisition in IDU and that this association is correlated with the mRNA expression level.

Distinct Trafficking of Cell Surface and Endosomal TIM-1 to the Immune Synapse

The T cell costimulatory molecule TIM-1 (T cell/transmembrane, mucin and immunoglobulin domain protein 1) sorts mainly to endosomes in lymphoid cells. At difference from the cell surface protein, endosomal TIM-1 translocates to the immune synapse (IS), where it can contribute to antigen-dependent T cell costimulation. TIM-1 ligands increase the amount of cell surface protein, preventing its traffic to the IS. The bipolar sorting of TIM-1 observed during IS formation is determined by differences in its subcellular location, and probably modulates antigen-driven immune responses.