The feed-forward loop between YB-1 and MYC is essential for multiple myeloma cell survival

Y-box binding protein 1 (YB-1) functions as a translational regulator and has been suggested to elevate MYC mRNA translation via an internal ribosome entry segment (IRES) point mutation in multiple myeloma (MM). We show that YB-1-mediated translation of MYC mRNA occurs independently of the reported IRES mutation, as 87 MM patients (n=88) and all tested human MM cell lines (HMCLs) were negative for the mutation. We show for the first time that positive MYC staining predicts YB-1 co-expression in malignant plasma cells and YB-1/MYC co-expression increases from 30% in medullary to 70% in extramedullary MM. YB-1 knockdown in HMCLs reduced both MYC protein levels and MYC mRNA in the polysomal fraction, providing a mechanism by which YB-1 controls MYC translation. MYC transcription of YB-1 is demonstrated in HMCLs as MYC knockdown resulted in reduced YB-1 protein and mRNA levels. Furthermore, MYC activation in non-malignant mouse embryonic fibroblasts (MEFs) increased YB-1 mRNA, clearly indicating that MYC drives YB-1 transcription. Importantly, perturbation of the MYC/YB-1 oncogenic circuit leads to apoptosis in HMCLs. Here, we demonstrate that these two proteins co-regulate each other via combined transcriptional/translational activity establishing their pivotal role in MM cell survival. We therefore suggest that targeting the YB-1/mRNA interaction provides a new strategy for MM drug development.

Surfactant protein A modulates release of reactive oxygen species from alveolar macrophages

The production and release of reactive oxygen species (the respiratory burst) is a common metabolic pathway linked to several macrophage-related reactions. The most abundant surfactant protein A (SP-A) binds to alveolar macrophages (AM) through a specific surface receptor with high affinity. Because such binding might initiate or modulate the respiratory burst, we wanted to know whether and how SP-A affects the oxygen radical release from AM. To answer these questions, we measured the release of reactive oxygen species from rat AM under various in vitro conditions using enhanced chemiluminescence systems. We prepared SP-A from pulmonary surfactant isolated either from silica-treated rats or adult dogs. Resident AM were harvested from pathogen-free Wistar rats by lung lavage. Adhered and nonadhered AM were assessed on protein-free or protein-coated surfaces of 96-well microtiter plates. On protein-free surfaces, the sole addition of SP-A failed to induce measurable oxygen radical release from 2 x 10(5) adhered or nonadhered AM, while zymosan opsonized with SP-A induced a marked increase over control. On protein-coated surfaces, AM respond differently depending on the coated protein: on SP-A-coated surfaces, a dose-dependent enhancement of oxygen radical release with a mean effective concentration of approximately 1.15 micrograms/ml was found. No such enhancement was seen on plates coated with similar amounts of either human fibronectin or collagen, and the enhancement with serum albumin was not dose related. Our data demonstrate that SP-A only enhances oxygen radical release from AM if SP-A is fixed to zymosan or the surface of the reaction vial in vitro.(ABSTRACT TRUNCATED AT 250 WORDS)

Host defence capacities of pulmonary surfactant: evidence for 'non-surfactant' functions of the surfactant system

The most well characterized function of pulmonary surfactant is its ability to reduce surface tension at the alveolar air-liquid interface, thereby preventing lung collapse. However, several lines of evidence suggest that surfactant may also have 'non-surfactant' functions: specific components of surfactant (proteins and phospholipids) may interact with different alveolar cells, inhaled particles and micro-organisms modulating pulmonary host defence systems. SP-A, the most abundant surfactant protein, binds to alveolar macrophages via a specific surface receptor with high affinity [128]. Such binding effects the release of reactive oxygen species from resident alveolar macrophages if SP-A is properly presented to the target cell. SP-A also stimulates chemotaxis of alveolar macrophages [142], and serves as an opsonin in the phagocytosis of herpes simplex virus [161] Candida tropicalis [138] and various bacteria [137]. In addition, SP-A enhances the uptake of particles by monocytes and culture-derived macrophages [140] and improves bacterial killing. SP-D, another hydrophobic surfactant-associated protein, might interact with alveolar macrophages as well, stimulating the release of oxygen radicals [148], while for the hydrophilic surfactant proteins SP-B and SP-C no macrophage interactions have been described so far. SP-A and SP-D are members of the so-called 'collectins', pattern recognition molecules involved in first line defence. While some surfactant proteins appear to stimulate certain macrophage defence functions, surfactant phospholipids seem to inhibit those of lymphocytes. Suppressed lymphocyte functions include lymphoproliferation in response to mitogens and alloantigens, B cell immunoglobulin production and natural killer cell cytotoxicity. Concerning surfactant's phospholipid composition phosphatidylglycerol is more suppressive than phosphatidylcholine on a molar basis [38]. Bovine surfactant has an immunosuppressive effect on the development of hypersensitivity pneumonitis in a guinea pig model [150]. Despite these interesting observations, several important questions concerning the interactions of surfactant components with pulmonary host defence systems remain unanswered. Sufficient host defence in the lungs works through various humoral-cellular systems in conjunction with the specific anatomy of the airways and the gas exchange surface--how does the surfactant system fit into this network? Surfactant and alveolar cells are both altered during lung injury--is there a relationship between alveolar cells from RDS patients and the endogenous surfactant isolated from such patients? How does exogenous surfactant as used for substitution therapy modulate the defence system of the host? Some of those artificial surfactants have been shown to inhibit the endotoxin-alveolar macrophages, PMNs and monocytes including IL-1, IL-6 and TNF [139,152].(ABSTRACT TRUNCATED AT 400 WORDS)

Error diffusion procedure: theory and applications in optical signal processing

An analysis of the error diffusion procedure is presented that is based on the terminology of filter theory. It is demonstrated that the error diffusion procedure is a powerful means to avoid signal error caused by a nonlinear system. An appropriate filter design method is described. The theoretical results are applied to treat picture binarization as well as quantization and coding in diffractive optics-digital holography.

Error-diffusion algorithm in phase synthesis and retrieval techniques

The treatment of phase synthesis and retrieval with the help of projection algorithms often suffers from a stagnation problem. A bandwidth constraint introduces undesired first-order zeros. From the incorporation of error diffusion the stagnation can be avoided.