Abstract
Despite the importance of microRNAs (miRs) for regulation of the delicate balance between cell proliferation and death, evidence for their specific involvement during death receptor (DR)-mediated apoptosis is scarce. Transfection with miR-133b rendered resistant HeLa cells sensitive to tumor necrosis factor-alpha (TNFα)-induced cell death. Similarly, miR-133b caused exacerbated proapoptotic responses to TNF-related apoptosis-inducing ligand (TRAIL) or an activating antibody to Fas/CD95. Comprehensive analysis, encompassing global RNA or protein expression profiling performed by microarray experiments and pulsed stable isotope labeling with amino acids in cell culture (pSILAC), led to the discovery of the antiapoptotic protein Fas apoptosis inhibitory molecule (FAIM) as immediate miR-133b target. Moreover, miR-133b impaired the expression of the detoxifying protein glutathione-S-transferase pi (GSTP1). Expression of miR-133b in tumor specimens of prostate cancer patients was significantly downregulated in 75% of the cases, when compared with matched healthy tissue. Furthermore, introduction of synthetic miR-133b into an ex-vivo model of prostate cancer resulted in impaired proliferation and cellular metabolic activity. PC3 cells were also sensitized to apoptotic stimuli after transfection with miR-133b similar to HeLa cells. These data reveal the ability of a single miR to influence major apoptosis pathways, suggesting an essential role for this molecule during cellular transformation, tumorigenesis and tissue homeostasis.
Highlights
Apoptosis, a strictly regulated form of active programmed cell death (PCD), plays crucial roles in a plethora of both homeostatic and pathological processes in multicellular organisms [1]
MiR-133b sensitizes cells to death receptor (DR)-mediated apoptosis In order to assess whether miR-133b possesses proapoptotic properties, we transfected HeLa cells with a synthetic miR-133b mimic or a negative scrambled control, stimulated them with tumor necrosis factor-alpha (TNFa) and characterized the cellular response by measuring independent apoptosis markers
Having proven miR-133b dysregulation in prostate cancer specimens, we addressed the question, whether reduced expression levels of proapoptotic miR-133b could be a mechanism that allows prostate cancer cells to circumvent cell death resulting in higher proliferation rate
Summary
A strictly regulated form of active programmed cell death (PCD), plays crucial roles in a plethora of both homeostatic and pathological processes in multicellular organisms [1]. Apoptotic cells are characterized by well-defined morphological changes some of which include rounding-up of the cell, reduction of cellular volume, chromatin condensation, nuclear fragmentation and membrane blebbing [2]. This process of controlled cellular suicide can be triggered by extracellular and intracellular stimuli, both of which result in activation of specific, yet partially overlapping signaling cascades. DRs oligomerize via their DD giving rise to a scaffold for the recruitment of several adaptor and signaling molecules At this death-inducing signaling complex (DISC), initiator caspases such as caspase 8 and 10 become activated by autocatalytic cleavage. The relevance of apoptosis and the proper function of its negative regulators for systemic homeostasis are exemplified by human patients suffering from devastating diseases like cancer, neurodegeneration or autoimmunity
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