slation Instead of acting as passengers in the mRNP journey from nucleus to cytoplasm, shuttling SR proteins actively engage in mRNA decay and translation thereby determining the ultimate fate of the bound mRNAs . Since spliced mRNP is assembled by EJC along Mol. Cells 2017; 40: 1-9 5 Multifunctional SR Proteins Sunjoo Jeong with SR proteins, mRNA decay process enhanced by EJC assembly on mRNA, such as non-sense mediated decay, can be regulated by SR proteins. In fact, SRSF1 have shown to enhance NMD of the premature termination codon containing model globin gene. SRSF1 have also reported to regulate the stability of PKCImRNA and regulate translation. Interestingly, it activates translation initiation by enhancing phosphorylation of 4E-BP1, a competitive inhibitor of cap-dependent translation, or represses translation of its own mRNA. Moreover, SRSF1 acts as an adaptor protein to recruit signaling molecules, such as mTORC1, during tumorigenesis or forms an aberrant proteosomal complex to stabilize p53 protein during senescence. These studies highlight the important role of SRSF1 as a splicing and translation regulator, which is relevant to RNA-mediated pathology. Of note, SRSF1 is overexpressed in some cancers and regulates alternative splicing of many cancer-related genes. Other shuttling SR proteins, such as SRSF3 and SRSF7, can also function in the translation process. SRSF3 has been shown to regulate Internal Ribosomal Entry Site mediated translation initiation, whereas SRSF7 plays a role in translation of un-spliced viral RNA containing Constitutive Transport Element . In the case of pdcd4 mRNA, SRSF3 has been shown to regulate nuclear alternative splicing and RNA export as well as cytoplasmic translation. These data suggest that SR proteins could act as coordinators for post-transcriptional steps of mRNAs from the nucleus to the cytoplasm. regulations of gene expression program in the cells. Since alternative splicing contributes to cellular physiology in various environments, it will be important to identify signaling pathways and critical signaling molecules relevant to SR protein regulation. Especially, the extracellular signals or environmental cues MedChemExpress YM-155 required for the regulation of SR protein expression should be investigated. It will be interesting to dissect the signaling pathways involved in SR protein modifications, including phosphorylation. ~~ Proteinprotein interactions influence all aspects of cellular life and the most direct mechanism through which proteins can influence each other PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19843186 is by physical interaction. This brings them into proximity to exert control on activity or to create opportunities for posttranslational modification. Proteinprotein associations often involve so-called linear binding motifs which are short protein regions lacking autonomous tertiary structure. These functional sites reside in intrinsically disordered protein regions and adopt stable conformation only upon binding. Currently, we can only guess how abundant linear motif-based 
interactions are; nevertheless, it was recently estimated that there are ~100,000 linear binding motifs targeting dedicated protein surfaces in the human proteome. As an example relevant to cellular signaling, mitogen-activated protein kinases are prototypical enzymes that depend on short segments from partner proteins and on their dedicated proteinprotein interaction hot spots. They mainly recognize their substrates not with the catalytic site but with auxiliary dockin