A novel group of Moraxella catarrhalis UspA proteins mediates cellular adhesion via CEACAMs and vitronectin.

Moraxella catarrhalis (Mx) is a common cause of otitis media and exacerbation of chronic obstructive pulmonary disease, an increasing worldwide problem. Surface proteins UspA1 and UspA2 of Mx bind to a number of human receptors and may function in pathogenesis. Genetic recombination events in the pathogen can generate hybrid proteins termed UspA2H. However, whether certain key functions (e.g. UspA1-specific CEACAM binding) can be exchanged between these adhesin families remains unknown. In this study, we have shown that Mx can incorporate the UspA1 CEACAM1-binding region not only into rare UspA1 proteins devoid of CEACAM-binding ability, but also into UspA2 which normally lack this capacity. Further, a screen of Mx isolates revealed the presence of novel UspA2 Variant proteins (UspA2V) in ∼14% of the CEACAM-binding population. We demonstrate that the expression of UspA2/2V with the CEACAM-binding domain enable Mx to bind both to cell surface CEACAMs and to integrins, the latter via vitronectin. Such properties of UspA2/2V have not been reported to date. The studies demonstrate that the UspA family is much more heterogeneous than previously believed and illustrate the in vivo potential for exchange of functional regions between UspA proteins which could convey novel adhesive functions whilst enhancing immune evasion.

VEGF165b, an inhibitory vascular endothelial growth factor splice variant: mechanism of action, in vivo effect on angiogenesis and endogenous protein expression.

Growth of new blood vessels (angiogenesis), required for all tumor growth, is stimulated by the expression of vascular endothelial growth factor (VEGF). VEGF is up-regulated in all known solid tumors but also in atherosclerosis, diabetic retinopathy, arthritis, and many other conditions. Conventional VEGF isoforms have been universally described as proangiogenic cytokines. Here, we show that an endogenous splice variant, VEGF(165)b, is expressed as protein in normal cells and tissues and is circulating in human plasma. We also present evidence for a sister family of presumably inhibitory splice variants. Moreover, these isoforms are down-regulated in prostate cancer. We also show that VEGF(165)b binds VEGF receptor 2 with the same affinity as VEGF(165) but does not activate it or stimulate downstream signaling pathways. Moreover, it prevents VEGF(165)-mediated VEGF receptor 2 phosphorylation and signaling in cultured cells. Furthermore, we show, with two different in vivo angiogenesis models, that VEGF(165)b is not angiogenic and that it inhibits VEGF(165)-mediated angiogenesis in rabbit cornea and rat mesentery. Finally, we show that VEGF(165)b expressing tumors grow significantly more slowly than VEGF(165)-expressing tumors, indicating that a switch in splicing from VEGF(165) to VEGF(165)b can inhibit tumor growth. These results suggest that regulation of VEGF splicing may be a critical switch from an antiangiogenic to a proangiogenic phenotype.

An adenovirus-mediated gene-transfer model of angiogenesis in rat mesentery.

OBJECTIVE: To develop an adenovirus-mediated angiogenesis model, dependent on VEGF, in a system amenable to functional characterization. METHODS: Adenovirus (AdV) expressing VEGF (Ad-VEGF) or GFP (Ad-EGFP) (1-3.3 x 10(8) TCID50/mL), and Monastral blue were injected into the fat pad on either side of a mesenteric connective tissue panel of halothane-anesthetized male Wistar rats after intravital microscopic imaging. The intestine was replaced in the animal, the laparotomy was sutured, and the animal was allowed to recover. Six days later, the same connective tissue panel was identified from the Monastral blue depot and the mesentery was imaged as before, and then excised, fixed, and stained for endothelial cells (GSL isolectin-1B4), proliferating cells, VEGF, VEGF-R2, and actin. The increase in fractional microvascular area (FVA) was measured, and proliferating cell density, sprout density, vessel branch point density, vessel density, and mean vessel length were determined. RESULTS: AdVEGF injection significantly increased the fractional vessel area (2.9 +/- 0.4-fold), proliferating endothelial cell density (1.7 +/- 0.1-fold), sprout density (3.1 +/- 0.3-fold), branch point density (1.9 +/- 0.1-fold), and the microvessel density (1.4 +/- 0.1-fold), and decreased the mean vessel length (0.69 +/- 0.04-fold). VEGF-R2 staining was evident near sprouting tips of endothelial cells, but not on the tip itself, and evidence for arteriogenesis was observed as well as clear evidence of angiogenesis. CONCLUSIONS: Ad-VEGF injection into the fat pad of the rat induced significant angiogenesis in the mesentery. This two-dimensional model of VEGF-induced angiogenesis is amenable to physiological, biochemical, and molecular assessment and may be a useful tool to help understand mechanisms of angiogenesis.