Xueming Tang

SENP3 is responsible for HIF-1 transactivation under mild oxidative stress via p300 de-SUMOylation

The physiological function of Sentrin/SUMO‐specific proteases (SENPs) remains largely unexplored, and little is known about the regulation of SENPs themselves. Here, we show that a modest increase of reactive oxygen species (ROS) regulates SENP3 stability and localization. We found that SENP3 is continuously degraded through the ubiquitin‐proteasome pathway under basal condition and that ROS inhibit this degradation. Furthermore, ROS causes SENP3 to redistribute from the nucleoli to the nucleoplasm, allowing it to regulate nuclear events. The stabilization and redistribution of SENP3 correlate with an increase in the transcriptional activity of the hypoxia‐inducing factor‐1 (HIF‐1) under mild oxidative stress. ROS‐enhanced HIF‐1 transactivation is blocked by SENP3 knockdown. The de‐SUMOylating activity of SENP3 is required for ROS‐induced increase of HIF‐1 transactivation, but the true substrate of SENP3 is the co‐activator of HIF‐1α, p300, rather than HIF‐1α itself. Removing SUMO2/3 from p300 enhances its binding to HIF‐1α. In vivo nude mouse xenografts overexpressing SENP3 are more angiogenic. Taken together, our results identify SENP3 as a redox sensor that regulates HIF‐1 transcriptional activity under oxidative stress through the de‐SUMOylation of p300.

Autografts and Xenografts of Skin Fibroblasts Delivering BMP-2 Effectively Promote Orthotopic and Ectopic Osteogenesis

Typical ex vivo bone morphogenetic protein‐2 (BMP‐2) gene therapy for localized bone formation usually utilizes bone marrow stromal cells as gene delivering cells. Skin fibroblasts, which are abundant and easily obtained, have potential advantages for autologous transplantation, but this application has not been adequately investigated. The purpose of this study was to determine the osteogenetic potential of fibroblasts delivering human BMP‐2 (hBMP‐2) gene by a retroviral system. The phenotypes of osteogenesis in human dermal fibroblasts transduced with hBMP‐2 were determined in vitro. Ectopic osteogenesis was evaluated following the injection of these cell xenografts into muscles of null mice, and the potential for orthotopic bone regeneration was evaluated from syngrafts and autografts of rat dermal fibroblasts in rat calvaria defects. The activity of alkaline phosphatase and expression of osteocalcin in fibroblasts transduced with hBMP‐2 were increased, and ectopic osteogenesis could be detected in muscles from null mice. The syngrafts and autografts of rat dermal fibroblasts transduced with hBMP‐2 gene significantly promoted bone repair and partially healed the calvarial defects. Syngrafts and autografts of rat fibroblasts transduced with hBMP‐2 gene had greater average areas exhibiting an osteogenic response compared with the control. The success of bone regeneration in calvaria defects induced by the autologous hBMP‐2‐modified skin fibroblasts provides evidence that fibroblasts could be effectively used in ex vivo gene therapy for local bone repair. Anat Rec, 292:777–786, 2009.

PML/RARα fusion protein mediates the unique sensitivity to arsenic cytotoxicity in acute promyelocytic leukemia cells: Mechanisms involve the impairment of cAMP signaling and the aberrant regulation of NADPH oxidase†

Acute promyelocytic leukemia (APL) cells are characterized by PML/RARα fusion protein, high responsiveness to arsenic trioxide (ATO)‐induced cytotoxicity and an abundant generation of reactive oxygen species (ROS). In this study we investigated the association among these three features in APL‐derived NB4 cells. We found that NADPH oxidase‐derived ROS generation was more abundant in NB4 cells compared with monocytic leukemia U937 cells. By using PR9, a sub‐line of U937 stably transduced with the inducible PML/RARα expression vectors, we attributed disparities on ROS generation and ATO sensitivity to the occurrence of PML/RARα fusion protein, since PML/RARα‐expressing cells appeared higher NADPH oxidase activity, higher ROS level and higher sensitivity to ATO. On the other hand, the basal intensity of cAMP signaling pathway was compared between NB4 and U937 as well as between PR9 cells with or without PML/RARα, demonstrating that PML/RARα‐expressing cells had an impaired cAMP signaling pathway which relieved its inhibitory effect on NADPH oxidase derived ROS generation. In summary, the present study demonstrated the correlation of PML/RARα with cAMP signaling pathway, NADPH oxidase and ROS generation in APL cells. PML/RARα that bestows NB4 cells various pathological features, paradoxically also endows these cells with the basis for susceptibility to ATO‐induced cytotoxcity. J. Cell. Physiol. 217: 486–493, 2008.