The survival and function of IL-10-producing regulatory B cells are negatively controlled by SLAMF5.

B cells have essential functions in multiple sclerosis and in its mouse model, experimental autoimmune encephalomyelitis, both as drivers and suppressors of the disease. The suppressive effects are driven by a regulatory B cell (Breg) population that functions, primarily but not exclusively, via the production of IL-10. However, the mechanisms modulating IL-10-producing Breg abundance are poorly understood. Here we identify SLAMF5 for controlling IL-10+ Breg maintenance and function. In EAE, the deficiency of SLAMF5 in B cells causes accumulation of IL10+ Bregs in the central nervous system and periphery. Blocking SLAMF5 in vitro induces both human and mouse IL-10-producing Breg cells and increases their survival with a concomitant increase of a transcription factor, c-Maf. Finally, in vivo SLAMF5 blocking in EAE elevates IL-10+ Breg levels and ameliorates disease severity. Our results suggest that SLAMF5 is a negative moderator of IL-10+ Breg cells, and may serve as a therapeutic target in MS and other autoimmune diseases.

Androgen receptor: a potential therapeutic target for glioblastoma.

The median survival time of patients with glioblastoma is still poor (14.6 month), partly due to a lack of effective treatment. We have observed that androgen receptor (AR) is amplified in glioblastomas at the DNA, RNA and protein levels. The AR gene was amplified in 27% of glioblastoma specimens from men (n=22) and of 38.2% from women (n=21). AR-RNA was overexpressed (>2.5 fold) in 93% (n=30), and AR-protein was induced (>two fold) in 56% of the glioblastomas samples (n=16). Thirty percent of the glioblastomas (n=21) also expressed a constitutively active AR-splice-variant (AR-V7/AR3) lacking the Ligand-Binding-Domain. Following these findings, we examined the effect of pharmacological inhibition of androgen receptor in vitro and in vivo, as well as of genetic silencing of the receptor in glioblastoma cell lines. AR antagonists, induced concentration-dependent death in three glioblastoma cell lines, as well as in two glioma initiating cell lines. Silencing of AR expression by siRNA induced cell death in the three tested glioblastoma cell lines. Enzalutamide given orally to nude mice bearing subcutaneous human glioma xenografts resulted in a 72% reduction in tumor volume (p=0.0027). The presence of AR-V7/AR3 in glioblastoma, together with the present data showing that genetic silencing of the full length AR in cell lines and pharmacological inhibition of AR, induce GBM cell death in vivo and in vitro, point to the important role of AR in GBM survival and render a potential therapeutic target for this devastating disease.

Mutant p53 gain of function underlies high expression levels of colorectal cancer stem cells markers.

Emerging notion in carcinogenesis ascribes tumor initiation and aggressiveness to cancer stem cells (CSCs). Specifically, colorectal cancer (CRC) development was shown to be compatible with CSCs hypothesis. Mutations in p53 are highly frequent in CRC, and are known to facilitate tumor development and aggressiveness. Yet, the link between mutant p53 and colorectal CSCs is not well-established. In the present study, we set to examine whether oncogenic mutant p53 proteins may augment colorectal CSCs phenotype. By genetic manipulation of mutant p53 in several cellular systems, we demonstrated that mutant p53 enhances colorectal tumorigenesis. Moreover, mutant p53-expressing cell lines harbor larger sub-populations of cells highly expressing the known colorectal CSCs markers: CD44, Lgr5, and ALDH. This elevated expression is mediated by mutant p53 binding to CD44, Lgr5, and ALDH1A1 promoter sequences. Furthermore, ALDH1 was found to be involved in mutant p53-dependent chemotherapy resistance. Finally, analysis of ALDH1 and CD44 in human CRC biopsies indicated a positive correlation between their expression and the presence of oncogenic p53 missense mutations. These findings suggest novel insights pertaining the mechanism by which mutant p53 enhances CRC development, which involves the expansion of CSCs sub-populations within CRC tumors, and underscore the importance of targeting these sub-populations for CRC therapy.

Post-translational regulation of p53 function through 20S proteasome-mediated cleavage.

The tumor suppressor p53 is a transcription factor that regulates the expression of a range of target genes in response to cellular stress. Adding to the complexity of understanding its cellular function is that in addition to the full-length protein, several p53 isoforms are produced in humans, harboring diverse expression patterns and functionalities. One isoform, Δ40p53, which lacks the first transactivation domain including the binding region for the negative regulator MDM2, was shown to be a product of alternative translation initiation. Here we report the discovery of an alternative cellular mechanism for Δ40p53 formation. We show that the 20S proteasome specifically cleaves the full-length protein (FLp53) to generate the Δ40p53 isoform. Moreover, we demonstrate that a dimer of FLp53 interacts with a Δ40p53 dimer, creating a functional hetero-tetramer. Consequently, the co-expression of both isoforms attenuates the transcriptional activity of FLp53 in a dominant negative manner. Finally, we demonstrate that following oxidative stress, at the time when the 20S proteasome becomes the major degradation machinery and FLp53 is activated, the formation of Δ40p53 is enhanced, creating a negative feedback loop that balances FLp53 activation. Overall, our results suggest that Δ40p53 can be generated by a 20S proteasome-mediated post-translational mechanism so as to control p53 function. More generally, the discovery of a specific cleavage function for the 20S proteasome may represent a more general cellular regulatory mechanism to produce proteins with distinct functional properties.