The RNA-binding protein RBM47 is a novel regulator of cell fate decisions by transcriptionally controlling the p53-p21-axis.

In recent years it has become more and more apparent that the regulation of gene expression by RNA-binding proteins (RBPs) is of utmost importance for most cellular signaling pathways. RBPs control several aspects of RNA biogenesis including splicing, localization, stability, and translation efficiency. One of these RBPs is RBM47 that recently has been suggested to function as a tumor suppressor as it was shown to suppress breast and colon cancer progression. Here we demonstrate that RBM47 is an important regulator of basal and DNA damage-induced p53 and p21WAF1/CIP1 protein expression. Knockdown of RBM47 by siRNAs results in a strong reduction in p53 mRNA and protein levels due to an impaired p53 promoter activity. Accordingly, overexpression of Flag-RBM47 enhances p53 promoter activity demonstrating that RBM47 regulates p53 at the transcriptional level. By controlling p53, knockdown of RBM47 concomitantly decreases also p21 expression at the transcriptional level, driving irradiated carcinoma cell lines from different entities into cell death rather than into senescence. Thus, RBM47 represents a novel molecular switch of cell fate decisions that functions as a regulator of the p53/p21-signaling axis.

An axiomatic characterization of the Borda mean rule.

A social dichotomy function maps a collection of weak orders to a set of dichotomous weak orders. Every dichotomous weak order partitions the set of alternatives into approved alternatives and disapproved alternatives. The Borda mean rule returns all dichotomous weak orders that approve all alternatives with above-average Borda score and disapprove alternatives with below-average Borda score. We show that the Borda mean rule is the unique social dichotomy function satisfying neutrality, reinforcement, faithfulness, and the quasi-Condorcet property. Our result holds for all domains of weak orders that are sufficiently rich, including the domain of all linear orders and the domain of all weak orders.

Kinesin-5 Blocker Monastrol Protects Against Bortezomib-Induced Peripheral Neurotoxicity.

Neurotoxicity is a relevant side effect of bortezomib treatment. Previous reports have shown that the development of peripheral neuropathy caused by anti-neoplastic agents may be a result of reduced axonal transport. Based on evidence from prior studies that the kinesin-5 inhibitor monastrol enhances axonal transport and improves neuronal regeneration, we focused on the neuroprotective role of monastrol during the chemotherapeutic treatment with bortezomib. Prolonged treatment of C57BL/6 mice with bortezomib induced a length-dependent small-fiber neuropathy with axonal atrophy and loss of sensory nerve fibers. The administration of monastrol substantially alleviated morphological features of axonal injury and functional measures of sensory neuropathy. Cytotoxicity studies in leukemia and multiple myeloma cell lines showed no interference of monastrol with the cytostatic effects of bortezomib. Our data indicate that the novel approach of targeting microtubule turnover by monastrol provides protection against bortezomib-induced neurotoxicity. The favorable cytotoxic profile of monastrol makes it an interesting candidate as neuroprotective agent in combined chemotherapy regimens that warrants further consideration.

The DEAD-box RNA helicase DDX41 is a novel repressor of p21WAF1/CIP1 mRNA translation.

The cyclin-dependent kinase inhibitor p21 is an important player in stress pathways exhibiting both tumor-suppressive and oncogenic functions. Thus, expression of p21 has to be tightly controlled, which is achieved by numerous mechanisms at the transcriptional, translational, and posttranslational level. Performing immunoprecipitation of bromouridine-labeled p21 mRNAs that had been incubated before with cytoplasmic extracts of untreated HCT116 colon carcinoma cells, we identified the DEAD-box RNA helicase DDX41 as a novel regulator of p21 expression. DDX41 specifically precipitates with the 3'UTR, but not with the 5'UTR, of p21 mRNA. Knockdown of DDX41 increases basal and γ irradiation-induced p21 protein levels without affecting p21 mRNA expression. Conversely, overexpression of DDX41 strongly inhibits expression of a FLAG-p21 and a luciferase construct, but only in the presence of the p21 3'UTR. Together, these data suggest that this helicase regulates p21 expression at the translational level independent of the transcriptional activity of p53. However, knockdown of DDX41 completely fails to increase p21 protein levels in p53-deficient HCT116 cells. Moreover, posttranslational up-regulation of p21 achieved in both p53+/+ and p53-/- HCT116 cells in response to pharmaceutical inhibition of the proteasome (by MG-132) or p90 ribosomal S6 kinases (by BI-D1870) is further increased by knockdown of DDX41 only in p53-proficient but not in p53-deficient cells. Although our data demonstrate that DDX41 suppresses p21 translation without disturbing the function of p53 to directly induce p21 mRNA expression, this process indirectly requires p53, perhaps in the form of another p53 target gene or as a still undefined posttranscriptional function of p53.

miR-30e controls DNA damage-induced stress responses by modulating expression of the CDK inhibitor p21WAF1/CIP1 and caspase-3.

MicroRNAs (miRNAs), a class of small non-coding RNAs that usually cause gene silencing by translational repression or degradation of mRNAs, are implicated in DNA damage-induced stress responses. To identify senescence-associated miRNAs, we performed microarray analyses using wild-type and p53-deficient HCT116 colon carcinoma cells that following gamma-irradiation (γIR) are driven into senescence and apoptosis, respectively. Several miRNAs including miR-30e were found upregulated in a p53-dependent manner specifically in senescent cells, but not in apoptotic cells. Overexpression of miR-30e in HCT116 cells not only inhibited γIR-, etoposide- or miR-34a-induced caspase-3-like DEVDase activities and cell death, but greatly accelerated and augmented their senescent phenotype. Consistently, procaspase-3 protein, but not mRNA decreased in the presence of miR-30e, whereas expression of the cyclin-dependent kinase inhibitor p21 increased both at the mRNA and protein level. Performing luciferase reporter gene assays, we identified the 3'-UTR of the caspase-3 mRNA as a direct miR-30e target. In contrast, although miR-30e was unable to bind to the p21 mRNA, it increased expression of a luciferase construct containing the p21 promoter, suggesting that the miR-30e-mediated upregulation of p21 occurs indirectly at the transcriptional level. Interestingly, despite suppressing procaspase-3 expression, miR-30e was unable to protect RKO colon carcinoma cells from DNA damage-induced death or to induce senescence, as miR-30e completely fails to upregulate p21 in these cells. These data suggest that miR-30e functions in a cell type-dependent manner as an important molecular switch for DNA damage-induced stress responses and may thus represent a target of therapeutic value.