Akt-ivation of RNA splicing

Recent advances in PTEN signalling axes in cancer

In over two decades since the discovery of phosphatase and tensin homologue deleted on chromosome 10 (PTEN), nearly 18,000 publications have attempted to elucidate its functions and roles in normal physiology and disease. The frequent disruption of PTEN in cancer cells was a strong indication that it had critical roles in tumour suppression. Germline PTEN mutations have been identified in patients with heterogeneous tumour syndromic diseases, known as PTEN hamartoma tumour syndrome (PHTS), and in some individuals with autism spectrum disorders (ASD). Today we know that by limiting oncogenic signalling through the phosphoinositide 3-kinase (PI3K) pathway, PTEN governs a number of processes including survival, proliferation, energy metabolism, and cellular architecture. Some of the most exciting recent advances in the understanding of PTEN biology and signalling have revisited its unappreciated roles as a protein phosphatase, identified non-enzymatic scaffold functions, and unravelled its nuclear function. These discoveries are certain to provide a new perspective on its full tumour suppressor potential, and knowledge from this work will lead to new anti-cancer strategies that exploit PTEN biology. In this review, we will highlight some outstanding questions and some of the very latest advances in the understanding of the tumour suppressor PTEN.

PTEN arginine methylation by PRMT6 suppresses PI3K-AKT signaling and modulates pre-mRNA splicing

Arginine methylation is a ubiquitous posttranslational modification that regulates critical cellular processes including signal transduction and pre-mRNA splicing. Here, we report that the tumor-suppressor PTEN is methylated by protein arginine methyltransferase 6 (PRMT6). Mass-spectrometry analysis reveals that PTEN is dimethylated at arginine 159 (R159). We found that PTEN is mutated at R159 in cancers, and the PTEN mutant R159K loses its capability to inhibit the PI3K-AKT cascade. Furthermore, PRMT6 is physically associated with PTEN, promotes asymmetrical dimethylation of PTEN, and regulates the PI3K-AKT cascade through PTEN R159 methylation. In addition, using transcriptome analyses, we found that PTEN R159 methylation is involved in modulation of pre-mRNA alternative splicing. Our results demonstrate that PTEN is functionally regulated by arginine methylation. We propose that PTEN arginine methylation modulates pre-mRNA alternative splicing and influences diverse physiologic processes.

Regulation of Shootin1 Gene Expression Involves NGF-induced Alternative Splicing during Neuronal Differentiation of PC12 Cells

Shootin1 is a protein involved in neuronal polarization, and has been shown to be a key molecule for the positive/negative feedback loop for axon induction required during neuronal symmetry breaking. To better understand the molecular basis of shootin1 dynamics, we analysed the regulatory pathways and the expressional status of shootin1 gene during NGF-induced neuronal differentiation. We demonstrated that the isoform-1 and isoform-2 of shootin1 is differentially expressed during neuronal differentiation. By blocking individual downstream pathways of NGF signalling, we found that PI3K/Akt pathway plays a major role in the expression of shootin1 isoform-2. Western blot and RT-PCR results showed that the isoform-1 of shootin1 is constitutively expressed, while the isoform-2 is expressed in a manner that is strictly dependent on NGF-stimulation. Isoform-specific RT-PCR results demonstrated that the differential expression of the isoform-1 and isoform-2 of shootin1 is a consequence of alternative splicing of shootin1 pre-mRNA, in response to NGF-signalling. Collectively these findings provide the first information on the molecular mechanisms regulating the expression of shootin1 gene and represent the first example of NGF-induced alternative splicing process that has a regulatory role in neuritogenesis.