PUMA mediates ER stress-induced apoptosis in portal hypertensive gastropathy

Mucosal apoptosis has been demonstrated to be an essential pathological feature in portal hypertensive gastropathy (PHG). p53-upregulated modulator of apoptosis (PUMA) was identified as a BH3-only Bcl-2 family protein that has an essential role in apoptosis induced by a variety of stimuli, including endoplasmic reticulum (ER) stress. However, whether PUMA is involved in mucosal apoptosis in PHG remains unclear, and whether PUMA induces PHG by mediating ER stress remains unknown. The aim of the study is to investigate whether PUMA is involved in PHG by mediating ER stress apoptotic signaling. To identify whether PUMA is involved in PHG by mediating ER stress, gastric mucosal injury and apoptosis were studied in both PHG patients and PHG animal models using PUMA knockout (PUMA-KO) and PUMA wild-type (PUMA-WT) mice. The induction of PUMA expression and ER stress signaling were investigated, and the mechanisms of PUMA-mediated apoptosis were analyzed. GES-1 and SGC7901 cell lines were used to further identify whether PUMA-mediated apoptosis was induced by ER stress in vitro. Epithelial apoptosis and PUMA were markedly induced in the gastric mucosa of PHG patients and mouse PHG models. ER stress had a potent role in the induction of PUMA and apoptosis in PHG models, and the apoptosis was obviously attenuated in PUMA-KO mice. Although the targeted deletion of PUMA did not affect ER stress, mitochondrial apoptotic signaling was downregulated in mice. Meanwhile, PUMA knockdown significantly ameliorated ER stress-induced mitochondria-dependent apoptosis in vitro. These results indicate that PUMA mediates ER stress-induced mucosal epithelial apoptosis through the mitochondrial apoptotic pathway in PHG, and that PUMA is a potentially therapeutic target for PHG.     

Puma, a critical mediator of cell death — one decade on from its discovery

PUMA (p53 upregulated modulator of apoptosis) is a pro-apoptotic member of the BH3-only subgroup of the Bcl-2 family. It is a key mediator of p53-dependent and p53-independent apoptosis and was identified 10 years ago. The PUMA gene is mapped to the long arm of chromosome 19, a region that is frequently deleted in a large number of human cancers. PUMA mediates apoptosis thanks to its ability to directly bind known anti-apoptotic members of the Bcl-2 family. It mainly localizes to the mitochondria. The binding of PUMA to the inhibitory members of the Bcl-2 family (Bcl-2-like proteins) via its BH3 domain seems to be a critical regulatory step in the induction of apoptosis. It results in the displacement of the proteins Bax and/or Bak. This is followed by their activation and the formation of pore-like structures on the mitochondrial membrane, which permeabilizes the outer mitochondrial membrane, leading to mitochondrial dysfunction and caspase activation. PUMA is involved in a large number of physiological and pathological processes, including the immune response, cancer, neurodegenerative diseases and bacterial and viral infections.     

Zinc Induces Expression of the BH3-only Protein PUMA Through p53 and ERK Pathways in SH-SY5Y Neuroblastoma Cells

Accumulating evidence suggests that zinc (Zn²⁺) contributes to neuronal death in pathologic states such as ischemia. p53-upregulated modulator of apoptosis (PUMA), which is a BH3-only protein, is known to promote apoptosis through a tumor suppressor p53-dependent and -independent mechanism. In this study, we examined the effect of Zn²⁺ on the induction of the PUMA gene in human neuroblastoma SH-SY5Y cells. The expression of PUMA was induced by Zn²⁺ in a dose- and time-dependent manner. A reporter assay revealed that Zn²⁺ activated the PUMA promoter. In addition, the mutation of the p53 binding site in the PUMA promoter region reduced promoter activation by Zn²⁺. These findings suggest that p53 participates in Zn²⁺-induced PUMA expression. Furthermore, we also demonstrated here that Zn²⁺ stimulates the phosphorylation of ERK and that the MEK-ERK pathway inhibitor, U0126, suppressed Zn²⁺-induced PUMA expression. Taken together, these results indicate that Zn²⁺ regulates the induction of PUMA through p53 and ERK pathways.     

PUMA-mediated apoptosis in fibroblast-like synoviocytes does not require p53

PUMA (p53-upregulated modulator of apoptosis) is a pro-apoptotic gene that can induce rapid cell death through a p53-dependent mechanism. However, the efficacy of PUMA gene therapy to induce synovial apoptosis in rheumatoid arthritis might have limited efficacy if p53 expression or function is deficient. To evaluate this issue, studies were performed to determine whether p53 is required for PUMA-mediated apoptosis in fibroblast-like synoviocytes (FLS). p53 protein was depleted or inhibited in human FLS by using p53 siRNA or a dominant-negative p53 protein. Wild-type and p53^-/- murine FLS were also examined to evaluate whether p53 is required. p53-deficient or control FLS were transfected with PUMA cDNA or empty vector. p53 and p21 expression were then determined by Western blot analysis. Apoptosis was assayed by ELISA to measure histone release and caspase-3 activation, or by trypan blue dye exclusion to measure cell viability. Initial studies showed that p53 siRNA decreased p53 expression by more than 98% in human FLS. Loss of p53 increased the growth rate of cells and suppressed p21 expression. However, PUMA still induced apoptosis in control and p53-deficient FLS after PUMA cDNA transfection. Similar results were observed in p53^-/- murine FLS or in human FLS transfected with a dominant-negative mutant p53 gene. These data suggest that PUMA-induced apoptosis in FLS does not require p53. Therefore, approaches to gene therapy that involve increasing PUMA expression could be an effective inducer of synoviocyte cell death in rheumatoid arthritis regardless of the p53 status in the synovium.     

PUMA与心肌细胞凋亡的研究进展

p53上调的凋亡调节物(p53 upregulated modulator of apoptosis,PUMA)是新近发现的一种具有促凋亡作用的p53靶基因.与以往发现的其他p53靶基因比较,PUMA在促凋亡作用中有两个重要的特点:一是PUMA几乎介导p53依赖的所有凋亡信号;二是PUMA不仅介导p53依赖的凋亡信号,而且还可以介导p53非依赖的凋亡信号.也就是说,尽管PUMA是p53靶基因,但是其在p53非依赖细胞凋亡中也发挥重要作用.由此可见,PUMA是一个强大的促凋亡因子.在心肌细胞,PUMA参与缺血/再灌注、内质网应激、阿霉素等多种刺激诱导的细胞凋亡.因此,PUMA在心肌细胞凋亡中发挥重要作用.     

Tumor-specific induction of apoptosis by a p53-reactivating compound

The tumor suppressor function of p53 is disabled in the majority of tumors, either by a point mutation of the p53 gene, or via MDM2-dependent proteasomal degradation. We have screened a chemical library using a cell-based assay and identified a low molecular weight compound named MITA which induced wild-type p53-dependent cell death in a variety of different types of human tumor cells, such as lung, colon and breast carcinoma cells, as well as in osteosarcoma and fibrosarcoma-derived cells. MITA inhibited p53-MDM2 interaction in vitro and in cells, which in turn prevented MDM2-mediated ubiquitination of p53 and resulted in a prolonged half-life and accumulation of p53 in tumor cells. Notably, p53 induction by MITA resulted in upregulated expression of p53 target genes MDM2, Bax, Gadd45 and PUMA, on protein and mRNA level. Importantly, neither p53 nor these target genes were induced in normal human fibroblasts (HDFs), which correlated with the absence of growth suppression in fibroblasts after treatment with MITA. However, upon activation of oncogenes in fibroblasts an induction and activation of p53 was observed, suggesting that activation of p53 by MITA occurs predominantly in tumor cells.     

PUMA inactivation protects against oxidative stress through p21/Bcl-XL inhibition of bax death

The tumor suppressor protein p53 activates growth arrest and proapoptotic genes in response to DNA damage. It is known that negative feedback by p21(Cip1/Waf1/Sdi1) represses p53-dependent transactivation of PUMA. The current study investigates PUMA feedback on p53 during oxidative stress from hyperoxia and the subsequent effects on cell survival mediated through p21 and Bcl-X(L). Deletion of PUMA in HCT116 colon carcinoma cells increased levels of p53 and p21, resulting in a larger G(1) population during hyperoxia. P21-dependent increase in Bcl-X(L) levels protected PUMA-deficient cells against hyperoxic cell death. Bax and Bak were both able to promote hyperoxic cell death. Bcl-X(L) protection against hyperoxic death was lost in cells lacking Bax, not PUMA, suggesting that Bcl-X(L) acts to inhibit Bax-dependent death. These results indicate that PUMA exerts a negative feedback on p53 and p21, leading to p21-dependent growth suppressive and survival changes. Enhanced survival was associated with increased Bcl-X(L) to block Bax activated cell death during oxidative stress.