Proliferating cell nuclear antigen is a novel inhibitory ligand for the natural cytotoxicity receptor NKp44

NK cells play an important role in the early immune response to cancer. The NKp44 activating receptor is the only natural cytotoxicity receptor that is expressed exclusively by primate NK cells, yet its cellular ligands remain largely unknown. Proliferating cell nuclear Ag (PCNA) is overexpressed in cancer cells. In this study, we show that the NKp44 receptor recognizes PCNA. Their interaction inhibits NK cell function through NKp44/ITIM. The physical interaction of NKp44 and PCNA is enabled by recruitment of target cell PCNA to the NK immunological synapse. We demonstrate that PCNA promotes cancer survival by immune evasion through inhibition of NKp44-mediated NK cell attack.     

Retinoic acid-induced modifications in the growth and cell surface components of a human carcinoma (HeLa) cell line

The addition of retinoic acid to cultures of HeLa-S3 cells caused a reduction in cell proliferation rate which became apparent after 72 h and was linearly dependent on retinoic acid concentration in the range 10⁻⁹–10⁻⁵ M. After 72 h of exposure to retinoic acid, the cells assumed a flattened appearance and no longer formed multilayers. These changes were reversed within 48 h after removal of retinoic acid from the medium. Structural analogs of retinoic acid with a free ---COOH group at C-15 were usually more potent in growth inhibition than compounds with an alcohol, aldehyde, ether or ester group. A cellular retinoic acid-binding protein was detected in cell homogenates, and the binding of [³H]retinoic acid to the binding protein was inhibited by most, but not all, analogs possessing a free terminal ---COOH group. For example, the 4-oxo analog of retinoic acid, while capable of inhibiting cellular proliferation, failed to bind to the retinoic acid-binding protein. Analysis of cell surface and cellular glycoproteins by lactoperoxidase-catalysed ¹²⁵I iodination and by metabolic labeling with [³H]glucosamine revealed that a 190000 D glycoprotein which was labeled by both methods and a 230000 D glycoprotein which was labeled only with [³H]glucosamine were labeled more intensely in retinoic acid-treated cells compared with untreated cells. The electrophoretic mobility of the 230000 D glycoprotein could be modified by treatment of intact cells with either neuraminidase or proteolytic enzymes, suggesting that this glycoprotein is also exposed on the cell surface. The cell surface alterations were detected much earlier than the onset of growth inhibition and appeared as early as 24 h after exposure to retinoic acid. The possible relationship between retinoic acid-induced changes in cell membrane structure, cell morphology, and cell proliferation is discussed.     

Estimating Cell Depth from Somatic Mutations

The depth of a cell of a multicellular organism is the number of cell divisions it underwent since the zygote, and knowing this basic cell property would help address fundamental problems in several areas of biology. At present, the depths of the vast majority of human and mouse cell types are unknown. Here, we show a method for estimating the depth of a cell by analyzing somatic mutations in its microsatellites, and provide to our knowledge for the first time reliable depth estimates for several cells types in mice. According to our estimates, the average depth of oocytes is 29, consistent with previous estimates. The average depth of B cells ranges from 34 to 79, linearly related to the mouse age, suggesting a rate of one cell division per day. In contrast, various types of adult stem cells underwent on average fewer cell divisions, supporting the notion that adult stem cells are relatively quiescent. Our method for depth estimation opens a window for revealing tissue turnover rates in animals, including humans, which has important implications for our knowledge of the body under physiological and pathological conditions.     

Substrate adhesion regulates sealing zone architecture and dynamics in cultured osteoclasts

The bone-degrading activity of osteoclasts depends on the formation of a cytoskeletal-adhesive super-structure known as the sealing zone (SZ). The SZ is a dynamic structure, consisting of a condensed array of podosomes, the elementary adhesion-mediating structures of osteoclasts, interconnected by F-actin filaments. The molecular composition and structure of the SZ were extensively investigated, yet despite its major importance for bone formation and remodelling, the mechanisms underlying its assembly and dynamics are still poorly understood. Here we determine the relations between matrix adhesiveness and the formation, stability and expansion of the SZ. By growing differentiated osteoclasts on micro-patterned glass substrates, where adhesive areas are separated by non-adhesive PLL-g-PEG barriers, we show that SZ growth and fusion strictly depend on the continuity of substrate adhesiveness, at the micrometer scale. We present a possible model for the role of mechanical forces in SZ formation and reorganization, inspired by the current data.     

A revision of the octocoral genus Ovabunda Alderslade, 2001 (Anthozoa,Octocorallia, Xeniidae)

The family Xeniidae (Octocorallia) constitutes an abundant benthic component on many Indo-West Pacific coral reefs and is ecologically important in the Red Sea. The genus Ovabunda Alderslade, 2001 was recently established to accommodate previous Xenia species with sclerites comprised of a mass of minute corpuscle-shaped microscleres. The aim of the present study was to examine type material of Xenia species in order to verify their generic affiliation. We present here a comprehensive account of the genus Ovabunda, using scanning electron microscopy to depict sclerite microstructure. We assign three Xenia species to the genus: O. ainex comb. n., O. gohari comb. n., and O. crenata comb. n.; and synonymize several other species of Ovabunda. We provide a key to Ovabunda species and conclude that they are mainly confined to the Red Sea, with some occurrence in the West Indian Ocean.     

Expanded population of activated antigen-engaged cells within the naive B cell compartment of patients with systemic lupus erythematosus

Polyclonal B cell activation is a well-described feature of systemic lupus erythematosus (SLE), but the immune mechanisms leading to this activation are unclear. To gain insight into these processes, we extensively characterized the activated peripheral blood B cell populations in SLE. PBMC from lupus patients and healthy controls were stained with various combinations of conjugated Ab to identify distinct peripheral B cell subsets, and activation was assessed by measurement of forward scatter and CD80 or CD86 expression using flow cytometry. SLE patients had altered proportions of several B cell subsets, many of which demonstrated increased activation as assessed by forward scatter. This activation occurred at an early developmental stage, as B cells in the transitional (T2) stage were already significantly larger than those seen in controls. Increased proportions of CD80- or CD86-expressing cells were also seen in multiple B cell subsets, with the most striking differences observed in the naive CD27-CD23+ population. Within the CD23+ subset, increased costimulatory molecule expression was most pronounced in an IgD+IgMlow population, suggesting that activation follows Ag engagement. Although controls also had IgD+IgMlowCD23+ cells, they were reduced in number and not activated. Thus, there is an altered response to Ig receptor engagement with self-Ags in lupus.     

Structural evidence for feedback activation by Ras.GTP of the Ras-specific nucleotide exchange factor SOS

Growth factor receptors activate Ras by recruiting the nucleotide exchange factor son of sevenless (SOS) to the cell membrane, thereby triggering the production of GTP-loaded Ras. Crystallographic analyses of Ras bound to the catalytic module of SOS have led to the unexpected discovery of a highly conserved Ras binding site on SOS that is located distal to the active site and is specific for Ras.GTP. The crystal structures suggest that Ras.GTP stabilizes the active site of SOS allosterically, and we show that Ras.GTP forms ternary complexes with SOS(cat) in solution and increases significantly the rate of SOS(cat)-stimulated nucleotide release from Ras. These results demonstrate the existence of a positive feedback mechanism for the spatial and temporal regulation of Ras.