Salah Mahmoudi

WRAP53 Is Essential for Cajal Body Formation and for Targeting the Survival of Motor Neuron Complex to Cajal Bodies

The WRAP53 protein regulates the formation and maintenance of Cajal bodies (nuclear sub-organelles), as well as directs the recruitment of nuclear factors to Cajal bodies.

The p53 target Wig-1 regulates p53 mRNA stability through an AU-rich element

The p53 target gene Wig-1 encodes a double-stranded-RNA-binding zinc finger protein. We show here that Wig-1 binds to p53 mRNA and stabilizes it through an AU-rich element (ARE) in the 3′ UTR of the p53 mRNA. This effect is mirrored by enhanced p53 protein levels in both unstressed cells and cells exposed to p53-activating stress agents. Thus, the p53 target Wig-1 is a previously undescribed ARE-regulating protein that acts as a positive feedback regulator of p53, with implications both for the steady-state levels of p53 and for the p53 stress response. Our data reveal a previously undescribed link between the tumor suppressor p53 and posttranscriptional gene regulation via AREs in mRNA.

Increasing the dynamic range of in situ PLA

Genomic DNA is the template of life - the entity which is characterized by a self-sustaining anatomical development, regulated signaling processes, the ability to reproduce and to respond to stimuli. Through what is classically known as the central dogma, the genome is transcribed into mRNA, which in turn is translated into proteins. The proteins take part in most, if not all, cellular processes, and it is by unraveling these processes that we can begin to understand life and disease-causing mechanisms.In vitro and in vivo assays are two levels at which protein communication may be studied, and which permit manipulation and control over the proteins under investigation. But in order to retrieve a representation of the processes as close to reality as possible, in situ analysis may instead be applied as a complement to the other two levels of study. In situ PLA offers the ability to survey protein activity in tissue samples and primary cell lines, at a single cell level, detecting single targets in their natural unperturbed environment. In this thesis new developments of the in situ PLA are described, along with a new technique offering in situ enzyme-free detection of proximity between biomolecules.The dynamic range of in situ PLA has now been increased by several orders of magnitude to cover analogous ranges of protein expression; the output signals have been modified to offer a greater signal-to-noise ratio and to limit false-positive-rates while also extending the dynamic range further; simultaneous detection of multiple protein complexes is now possible; proximity-HCR is presented as a robust and inexpensive enzyme-free assay for protein complex detection.The thesis also covers descriptions on how the techniques may be simultaneously applied, also together with other techniques, for the multiple data-point acquisition required by the emerging realm of systems biology. A future perspective is presented for how much more information may be simultaneously acquired from tissue samples to describe biomolecular interactions in a new manner. This will allow new types of biomarkers and drugs to be discovered, and a new holistic understanding of life.

CDK-mediated activation of the SCFFBXO28 ubiquitin ligase promotes MYC-driven transcription and tumourigenesis and predicts poor survival in breast cancer

SCF (Skp1/Cul1/F‐box) ubiquitin ligases act as master regulators of cellular homeostasis by targeting key proteins for ubiquitylation. Here, we identified a hitherto uncharacterized F‐box protein, FBXO28 that controls MYC‐dependent transcription by non‐proteolytic ubiquitylation. SCFFBXO28 activity and stability are regulated during the cell cycle by CDK1/2‐mediated phosphorylation of FBXO28, which is required for its efficient ubiquitylation of MYC and downsteam enhancement of the MYC pathway. Depletion of FBXO28 or overexpression of an F‐box mutant unable to support MYC ubiquitylation results in an impairment of MYC‐driven transcription, transformation and tumourigenesis. Finally, in human breast cancer, high FBXO28 expression and phosphorylation are strong and independent predictors of poor outcome. In conclusion, our data suggest that SCFFBXO28 plays an important role in transmitting CDK activity to MYC function during the cell cycle, emphasizing the CDK‐FBXO28‐MYC axis as a potential molecular drug target in MYC‐driven cancers, including breast cancer.

WRAP53 promotes cancer cell survival and is a potential target for cancer therapy

We previously identified WRAP53 as an antisense transcript that regulates the p53 tumor suppressor. The WRAP53 gene also encodes a protein essential for Cajal body formation and involved in cellular trafficking of the survival of motor neuron complex, the telomerase enzyme and small Cajal body-specific RNAs to Cajal bodies. Here, we show that the WRAP53 protein is overexpressed in a variety of cancer cell lines of different origin and that WRAP53 overexpression promotes cellular transformation. Knockdown of the WRAP53 protein triggers massive apoptosis through the mitochondrial pathway, as demonstrated by Bax/Bak activation, loss of mitochondrial membrane potential and cytochrome c release. The apoptosis induced by WRAP53 knockdown could moreover be blocked by Bcl-2 overexpression. Interestingly, human tumor cells are more sensitive to WRAP53 depletion as compared with normal human cells indicating that cancer cells in particular depends on WRAP53 expression for their survival. In agreement with this, we found that high levels of WRAP53 correlate with poor prognosis of head and neck cancer. Together these observations propose a role of WRAP53 in carcinogenesis and identify WRAP53 as a novel molecular target for a large fraction of malignancies.

Extract from Asteraceae Brachylaena ramiflora induces apoptosis preferentially in mutant p53-expressing human tumor cells

The p53 tumor suppressor gene is inactivated by point mutation in a large fraction of human tumors, allowing evasion of apoptosis and tumor progression. p53 mutation is often associated with increased resistance to therapy. Pharmacological reactivation of mutant p53 is an attractive therapeutic strategy. We previously identified p53 reactivation and induction of massive apoptosis, a low-molecular weight compound that suppresses the growth of cancer cells in a mutant p53-dependent manner. Here, we report the identification and characterization of an extract from the terrestrial plant Brachylaena ramiflora (Asteraceae) that preferentially induces apoptosis in human tumor cells expressing mutant p53. Further analysis of this extract and identification of active compounds may provide novel structural scaffolds for the development of mutant p53-targeting anticancer drugs.