A novel endothelial-specific heat shock protein HspA12B is required in both zebrafish development and endothelial functions in vitro

Heat shock cognate protein 70 is essential for Akt signaling in endothelial function

OBJECTIVE

Heat shock protein 70s (Hsp70s) are molecular chaperones that protect cells from damage in response to various stress stimuli. However, the functions and mechanisms in endothelial cells (ECs) have not been examined. Herein, we investigate the role of Hsp70s, including heat shock cognate protein 70 (Hsc70), which is constitutively expressed in nonstressed cells (ie, ECs).

METHODS AND RESULTS

The Hsp70 inhibitor, KNK437, significantly decreased vascular endothelial growth factor (VEGF)-induced cell migration and tube formation in vitro. KNK437 inhibited the phosphorylation of VEGF-induced Akt and endothelial nitric oxide synthase (eNOS) in human umbilical vein endothelial cells. In a mouse hind limb model of vascular insufficiency, intramuscular inhibition of Hsp70s attenuated collateral and capillary vessel formation. Silencing the Hsc70 gene by short interfering RNA abolished VEGF-induced Akt phosphorylation and VEGF-stimulated human umbilical vein endothelial cell migration and tube formation. As the molecular mechanisms, Hsc70 knockdown reduced the expression of phosphatidylinositol 3-kinase.

CONCLUSIONS

Collectively, Hsc70 plays a significant role in ECs via the phosphatidylinositol 3-kinase/Akt pathway. Hsc70 may provide the basis for the development of new therapeutic strategies for angiogenesis.

Analysis of genes isolated from plated hemocytes of the Pacific oyster, Crassostreas gigas

A complementary deoxyribonucleic acid library was constructed from hemocytes of Crassostrea gigas that had been plated on poly-lysine plates for 24 h. From this library, 2,198 expressed sequence tags (ESTs) of greater than or equal to 100 bp were generated and analyzed. A large number of genes that potentially could be involved in the physiology of the oyster hemocyte were uncovered. They included proteins involved in cytoskeleton rearrangement, proteases and antiproteases, regulators of transcription and translation, cell death regulators, receptors and their associated protein factors, lectins, signal transduction proteins, and enzymes involved in eicosanoid and steroid synthesis and xenobiotic metabolism. Based on their relationship with innate immunity, the expression of selected genes was analyzed by quantitative polymerase chain reaction in gills from bacterial-challenged oysters. Several genes observed in the library were significantly upregulated by bacterial challenge including interleukin 17, astacin, cystatin B, the EP4 receptor for prostaglandin E, the ectodysplasin receptor, c-jun, and the p100 subunit of nuclear factor-kB. Using a similar approach, we have been analyzing the genes expressed in trout macrophages. While there are significant differences between the types of genes present in vertebrate macrophages compared with oyster hemocytes, there are some striking similarities including proteins involved in cytoskeletal rearrangement, proteases and antiproteases, and genes involved in certain signal transduction pathways underlying immune processes such as phagocytosis. Finally, C. virginica homologs of some of the C. gigas genes uncovered in the ESTs were obtained by aligning the ESTs reported here, against the assembled C. virginica ESTs at the National Center for Biotechnology Information.

Zebrafish Jak2a plays a crucial role in definitive hematopoiesis and blood vessel formation

We examined the role of zebrafish (Danio rerio) Jak2a, a homolog of mammalian Jak2, in the developing embryo by injecting in vitro synthesized Jak2a shRNA into zebrafish zygotes. Blood circulation was suppressed in Jak2a shRNA-injected embryos from 24hours post fertilization (hpf) and all embryos died with enlarged pericardium, shortened body lengths, and defects in some vasculature within 8 days post fertilization. O-dianisidine staining of red blood cells revealed normal blood island formation with no circulating red blood cells. As in Jak2(-/-) transgenic mice, expression of definitive Ba1 globin was significantly reduced in Jak2a knockdown embryos at 36hpf, whereas expression of other hematopoietic markers, primitive be1 globin, gata-1, and scl, were unaffected. More importantly, blood vessel formation was disturbed in Jak2a knockdown embryos as revealed by alkaline phosphatase staining at 72hpf. Thus, our data indicate that zebrafish Jak2a is important in both definitive hematopoiesis and blood vessel formation.

Heat shock proteins: essential proteins for apoptosis regulation

Many different external and intrinsic apoptotic stimuli induce the accumulation in the cells of a set of proteins known as stress or heat shock proteins (HSPs). HSPs are conserved proteins present in both prokaryotes and eukaryotes. These proteins play an essential role as molecular chaperones by assisting the correct folding of nascent and stress-accumulated misfolded proteins, and by preventing their aggregation. HSPs have a protective function, that is they allow the cells to survive to otherwise lethal conditions. Various mechanisms have been proposed to account for the cytoprotective functions of HSPs. Several of these proteins have demonstrated to directly interact with components of the cell signalling pathways, for example those of the tightly regulated caspasedependent programmed cell death machinery, upstream, downstream and at the mitochondrial level. HSPs can also affect caspase-independent apoptosis-like process by interacting with apoptogenic factors such as apoptosis-inducing factor (AIF) or by acting at the lysosome level. This review will describe the different key apoptotic proteins interacting with HSPs and the consequences of these interactions in cell survival, proliferation and apoptotic processes. Our purpose will be illustrated by emerging strategies in targeting these protective proteins to treat haematological malignancies.