MicroRNA miR-93 promotes tumor growth and angiogenesis by targeting integrin-ß8.

It has been reported that the miR-106b∼25 cluster, a paralog of the miR-17∼92 cluster, possesses oncogenic activities. However, the precise role of each microRNA (miRNA) in the miR-106b∼25 cluster is not yet known. In this study, we examined the function of miR-93, one of the microRNAs within the miR-106b∼25 cluster, in angiogenesis and tumor formation. We found that miR-93 enhanced cell survival, promoted sphere formation and augmented tumor growth. Most strikingly, when miR-93-overexpressing U87 cells were co-cultured with endothelial cells, they supported endothelial cell spreading, growth, migration and tube formation. In vivo studies revealed that miR-93-expressing cells induced blood vessel formation, allowing blood vessels to extend to tumor tissues in high densities. Angiogenesis promoted by miR-93 in return facilitated cell survival, resulting in enhanced tumor growth. We further showed that integrin-ß8 is a target of miR-93. Higher levels of integrin-ß8 are associated with cell death in tumor mass and in human glioblastoma. Silencing of integrin-ß8 expression using small interfering RNA promoted cell proliferation, whereas ectopic expression of integrin-ß8 decreased cell growth. These findings showed that miR-93 promotes tumor growth and angiogenesis by suppressing, at least in part, integrin-ß8 expression. Our results suggest that inhibition of miR-93 function may be a feasible approach to suppress angiogenesis and tumor growth.

Comparative proteomic analysis identifies protein disulfide isomerase and peroxiredoxin 1 as new players involved in embryonic interdigital cell death.

In this study, we used comparative proteomics to identify proteins that were involved in the regulation of interdigital cell death. The protein profiles of embryonic day (E) 12.5 and 13.5 mouse hindlimb interdigital tissues were compared to identify proteins that were differentially expressed. The interdigital cells are irreversibly committed to programmed cell death (PCD) at E13.5, whereas they are developmentally plastic at E12.5. We established that protein disulfide isomerase (PDI) expression was up-regulated at E13.5, while peroxiredoxin 1 (Prdx1) expression was down-regulated at this time point. Semiquantitative reverse transcriptase-polymerase chain reaction and Western blot analyses confirmed the data obtained from the two-dimensional electrophoresis gels. Furthermore, we were able to up-regulate PDI expression by manipulating the E12.5 interdigital tissues to die during culture, although this up-regulation was not possible when cell survival was promoted. In addition, we could inhibit interdigital cell death and expression of proapoptotic genes (Bmp-4 and Bambi) by treating interdigital tissues with PDI antibodies and bacitracin (a PDI enzyme inhibitor). These findings suggested that PDI was involved in the activation and maintenance of interdigital cell death. Conversely, we determined that Prdx1 expression was maintained when interdigital cultures were manipulated to survive but down-regulated when the cultures were permitted to die. The result suggested that Prdx1 was involved in maintaining interdigital cell survival. However, we were unable to induce interdigital cell death by means of RNA interference-mediated silencing of Prdx1 expression, indicating that Prdx1 down-regulation is not sufficient for PCD to occur. Proteomic analysis of the Prdx1 knock-down cells revealed that the level of NF-kappaB inhibitor epsilon (IkappaBepsilon) was dramatically reduced. Furthermore, we found an increase in NFkappaB activation and reactive oxygen species (ROS) levels in the cytoplasm as a result of Prdx1 knockdown. We also found that silencing Prdx1 made the interdigital cells more susceptible to ROS-induced cell death. Taken together, our study identifies two new players in interdigital cell death and highlights that PCD is regulated by a delicate balance of proapoptotic and survival-promoting activities.