Inhibitory Member Of Apoptosis-stimulating Proteins Research Articles

FHL2 interacts with iASPP and impacts the biological functions of leukemia cells.

iASPP is an inhibitory member of apoptosis-stimulating proteins of p53 (ASPP) family, which inhibits p53-dependent apoptosis. iASPP was highly expressed in acute leukemia, inhibited leukemia cells apoptosis and promoted leukemogenesis. In order to clarify its mechanism, a yeast two-hybrid screen was performed and FHL2 was identified for the first time as one of the binding proteins of iASPP. FHL2 was highly expressed in K562 and Kasumi-1 cells. FHL2 and iASPP interacted with each other and co-localized in both nucleus and cytoplasm. Either FHL2 or iASPP silenced could reduce cell proliferation, induce cell cycle arrest at G0/G1 phase, and increase cell apoptosis. Western blot analysis showed that the level of p21 and p27 increased, CDK4, E2F1, Cyclin E and anti-apoptotic proteins Bcl-2 and Bcl-xL reduced. Interestingly, when FHL2 was knocked down, the protein expression level of iASPP also decreased. Similarly, the expression of FHL2 would reduce when iASPP was silenced. These results indicated that FHL2 might be a novel potential target for acute myelocytic leukemia treatment.

MicroRNA-124–Mediated Regulation of Inhibitory Member of Apoptosis-Stimulating Protein of p53 Family in Experimental Stroke

p53-mediated neuronal death is a central pathway of stroke pathophysiology, but its mechanistic details remain unclear. Here, we identified a novel microRNA mechanism that downregulation of inhibitory member of the apoptosis-stimulating proteins of p53 family (iASPP) by the brain-specific microRNA-124 (miR-124) promotes neuronal death after cerebral ischemia. In a mouse model of focal permanent cerebral ischemia, the expression of iASPP and miR-124 was quantified by reverse transcription quantitative real-time polymerase chain reaction, immunofluorescence staining, and Western blot. Luciferase reporter assay was used to validate whether miR-124 can directly bind to the 3'-untranslated region of iASPP mRNA. To evaluate the role of miR-124, miR-124 mimic and its inhibitor were transfected into Neuro-2a cells and C57 mice. There was no change in the iASPP mRNA level in cerebral ischemia. However, iASPP protein was remarkably decreased, with a concurrent elevation in miR-124 level. Furthermore, miR-124 can bind to the 3'-untranslated region of iASPP in 293T cells and downregulate its protein levels in Neuro-2a cells. In vivo, infusion of miR-124 decreased brain levels of iASPP, whereas inhibition of miR-124 enhanced iASPP levels and significantly reduced infarction in mouse focal cerebral ischemia. These data demonstrate that p53-mediated neuronal cell death after stroke can be nontranscriptionally regulated by a novel mechanism involving suppression of endogenous cell death inhibitors by miR-124. Further dissection of microRNA regulatory mechanisms may lead to new therapeutic opportunities for preventing neuronal death after stroke.

IASPP inhibits p53-independent apoptosis by inhibiting transcriptional activity of p63/p73 on promoters of proapoptotic genes

The ability to induce apoptosis is the most important tumor-suppression function of p53. Inhibitory member of apoptosis-stimulating protein of p53 family (iASPP) is an apoptotic-specific regulator of p53. iASPP suppresses apoptosis by inhibiting the transactivation function of p53 on the promoters of proapoptotic genes; however, the mechanism whereby iASPP influences apoptosis in tumor cells with mutant or deficient p53 has not been completely defined. In this study, we investigated the role of iASPP in the p63/p73 apoptosis pathway. iASPP inhibited apoptosis independently of p53 in tumor cells, mainly by inhibiting the transcriptional activity of p63/p73 on the promoters of proapoptotic genes. Because p63 and p73 are rarely mutated in human cancers, inhibiting the expression of endogenous iASPP may provide a useful strategy for restoring the apoptotic activity of p63 and p73 in human tumors with p53 loss or mutation. These results represent a promising new strategy for the treatment of cancers with non-wild-type p53.