Immune adaptor ADAP in T cells regulates HIV-1 transcription and cell-cell viral spread via different co-receptors.

BACKGROUND: Immune cell adaptor protein ADAP (adhesion and degranulation-promoting adaptor protein) mediates aspects of T-cell adhesion and proliferation. Despite this, a connection between ADAP and infection by the HIV-1 (human immunodeficiency virus-1) has not been explored. RESULTS: In this paper, we show for the first time that ADAP and its binding to SLP-76 (SH2 domain-containing leukocyte protein of 76 kDa) regulate HIV-1 infection via two distinct mechanisms and co-receptors. siRNA down-regulation of ADAP, or expression of a mutant that is defective in associating to its binding partner SLP-76 (termed M12), inhibited the propagation of HIV-1 in T-cell lines and primary human T-cells. In one step, ADAP and its binding to SLP-76 were needed for the activation of NF-κB and its transcription of the HIV-1 long terminal repeat (LTR) in cooperation with ligation of co-receptor CD28, but not LFA-1. In a second step, the ADAP-SLP-76 module cooperated with LFA-1 to regulate conjugate formation between T-cells and dendritic cells or other T-cells as well as the development of the virological synapse (VS) and viral spread between immune cells. CONCLUSIONS: These findings indicate that ADAP regulates two steps of HIV-1 infection cooperatively with two distinct receptors, and as such, serves as a new potential target in the blockade of HIV-1 infection.

Non-cleavable talin rescues defect in the T-cell conjugation of T-cells deficient in the immune adaptor SKAP1.

While the cytoskeletal protein talin binds to the ß-chain of LFA-1, the immune cell adaptor SKAP1 (SKAP-55) binds to the α-chain of the same integrin via RapL. Whereas calpain protease cleavage of talin is important for LFA-1 activation, it has been unclear whether SKAP1 can alter the function of talin or its associated adaptor RIAM in T-cells. In this paper, we report that Skap1-/- T-cells showed a reduction in the translocation of talin and RIAM to the contact interface of T-cells with antigenic beads or dendritic cells (DCs) presenting OVA peptide to OT-1 T-cells. In addition, Skap1-/- T-cells show an altered pattern of talin cleavage, while the expression of a cleavage resistant form of talin (L432G) restored the impaired adhesion of OT1 transgenic Skap1-/- T-cells with DCs. SKAP1 therefore can affect the function of talin in T-cells needed for optimal T-cell/DC conjugation.

Immunopathologies linked to integrin signalling.

Integrin binding to ligand plays essential roles in the differentiation and function of mammalian cells. beta2 integrins in leukocytes are needed for migration to sites of inflammation and in lymph nodes as well as for cellular events such as phagocytosis and the formation of the conjugates between T cells and antigen-presenting cells. In T cells, integrin adhesion is activated primarily by the antigen-receptor (TCR complex) and chemokines in a process known as 'inside-out' signalling. Great progress has been made in identifying mutations that are responsible for leukocyte adhesion deficiency (LAD) syndromes, a disorder that presents with an impaired ability to clear pathogens and recurrent life-threatening infections. LAD mutations have been identified with defects in integrins, fucosylation and in the new intracellular mediator kindlin-3. Here, we review the key players in the 'inside-out' and 'outside-in' signalling pathways that will serve as new potential targets in the design of novel therapeutics to treat various immunodeficiencies.

Silencing the Metallothionein-2A gene induces entosis in adherent MCF-7 breast cancer cells.

The presence of a live cell cohabiting within another cell has fascinated scientists for many decades. Far from being a spurious event, many have attempted to uncover the molecular mechanism underlying this phenomenon. In this study, we observed anchorage-dependent MCF-7 cells internalizing neighboring epithelial cells (entosis) after siRNA-mediated silencing of the Metallothionein-2A (MT-2A) gene. MTs belong to a family of low-molecular weight proteins, which bind metal ions endogenously and its over-expression has been reported in a variety of cancers that include breast, prostate, and colon. We provide microscopic evidence at light and ultrastructural levels of the occurrence of entosis after altering MT expression in a subpopulation of MCF-7 breast cancer cells by silencing the MT-2A gene. Our results demonstrate that adheren junctions may play important roles in the formation of cell-in-cell cytostructure after MT-2A gene downregulation and the entotic process does not appear to involve genes associated with autophagy. Interiorized cells often underwent lysosomal degradation within the cytoplasmic body of the engulfing cell. It would appear that a subset of breast cancer cells could die via entosis after MT-2A gene silencing.

Silencing the Metallothionein-2A gene inhibits cell cycle progression from G1- to S-phase involving ATM and cdc25A signaling in breast cancer cells.

Metallothioneins (MTs) are a group of metal-binding proteins involved in cell proliferation, differentiation and apoptosis. The MT-2A isoform is generally the most abundant isoform among the 10 known functional MT genes. In the present study, we observed that down-regulation of the MT-2A gene in MCF-7 cells via siRNA-mediated silencing inhibited cell growth by inducing cell cycle arrest in G1-phase (G1-arrest) and a marginal increase in cells in sub-G1-phase. Scanning electron microscopic examination of the cells with silenced expression of MT-2A (siMT-2A cells) revealed essentially normal cell morphology with presence of scattered apoptotic cells. To elucidate the underlying molecular mechanism, we examined the expression of cell cycle related genes in MT-2A-silenced cells and found a higher expression of the ataxia telangiectasia mutated (ATM) gene concomitant with a lower expression of the cdc25A gene. These data suggest that MT-2A could plausibly modulate cell cycle progression from G1- to S-phase via the ATM/Chk2/cdc25A pathway.

Purification, crystallization and X-ray analysis of Hibiscus chlorotic ringspot virus.

Hibiscus chlorotic ringspot virus (HCRSV), a Carmovirus, occurs worldwide and induces chlorotic ringspots on leaves, stunting and flower distortion in Hibiscus species, including kenaf. The HCRSV capsid has T = 3 icosahedral symmetry and contains 180 copies of the coat protein. A virus yield of 48-70 mg per 100 g of infected kenaf leaves was achieved with an improved purification scheme involving sucrose-cushion and sucrose density-gradient centrifugation. The virus was crystallized using PEG 8000 and 2,3-butanediol as co-precipitants. The crystals belonged to the cubic space group P23, with unit-cell parameter a = 392 A, and diffracted X-rays to at least 4.5 A resolution.