ABSTRACT
The Gi-coupled somatostatin receptor 2 (SST2) is a G protein-coupled receptor (GPCR) that mediates many of somatostatin's neuroendocrine actions. Upon stimulation, SST2 is rapidly internalized and transported to early endosomes before being recycled to the plasma membrane. However, little is known about the intracellular itinerary of SST2 after it moves to the early endosomal compartment or the cytoplasmic proteins that regulate its trafficking. As postsynaptic density protein/discs large 1/zonula occludens-1 (PDZ) domain interactions often regulate the trafficking and signaling potential of GPCRs, we examined the role of the SST2 PDZ ligand and additional C-terminal residues in controlling its intracellular trafficking. We determined that SST2 can recycle to the plasma membrane via multiple pathways, including a LAMP1/Rab7-positive late endosome to the trans-Golgi network (TGN) pathway. Trafficking from the late endosome to the TGN is often regulated by the retromer complex of endosomal coat proteins, and disrupting the retromer components sorting nexins 1/2 inhibits the budding of SST2 from late endosomes. Moreover, trafficking through the late endosomal/TGN pathway is dependent on an intact PDZ ligand and C-terminal tail, as truncating either the 3 or 10 C-terminal amino acids of SST2 alters the pathway through which it recycles to the plasma membrane. Moreover, addition of these amino acids to a heterologous receptor is sufficient to redirect it from a degradation pathway to a recycling itinerary. Our results demonstrate that endosomal trafficking of SST2 is dependent on numerous regulatory mechanisms controlled by its C terminus and the retromer machinery.
Subject(s)
Cell Membrane/metabolism , Endosomes/metabolism , Membrane Proteins/metabolism , Receptors, Somatostatin/metabolism , trans-Golgi Network/metabolism , Amino Acid Motifs , Amino Acid Sequence , Base Sequence , HEK293 Cells , Humans , Multiprotein Complexes/metabolism , Nucleotide Motifs , PDZ Domains , Protein Transport , Receptors, Somatostatin/chemistry , Receptors, Somatostatin/genetics , Signal TransductionSubject(s)
Everolimus/therapeutic use , Hypoglycemia/drug therapy , Insulinoma/diagnosis , Neoplasm Recurrence, Local/diagnosis , Pancreatic Neoplasms/diagnosis , Aged , Humans , Insulin/blood , Insulinoma/drug therapy , Insulinoma/pathology , Insulinoma/physiopathology , Male , Neoplasm Recurrence, Local/drug therapy , Neoplasm Recurrence, Local/pathology , Neoplasm Recurrence, Local/physiopathology , Pancreatectomy , Pancreatic Neoplasms/drug therapy , Pancreatic Neoplasms/pathology , Pancreatic Neoplasms/physiopathology , Quality of Life , Treatment OutcomeABSTRACT
A deeper mechanistic understanding of tumour angiogenesis regulation is needed to improve current anti-angiogenic therapies. Here we present evidence from systems-based miRNA analyses of large-scale patient data sets along with in vitro and in vivo experiments that miR-192 is a key regulator of angiogenesis. The potent anti-angiogenic effect of miR-192 stems from its ability to globally downregulate angiogenic pathways in cancer cells through regulation of EGR1 and HOXB9. Low miR-192 expression in human tumours is predictive of poor clinical outcome in several cancer types. Using 1,2-dioleoyl-sn-glycero-3-phosphatidylcholine (DOPC) nanoliposomes, we show that miR-192 delivery leads to inhibition of tumour angiogenesis in multiple ovarian and renal tumour models, resulting in tumour regression and growth inhibition. This anti-angiogenic and anti-tumour effect is more robust than that observed with an anti-VEGF antibody. Collectively, these data identify miR-192 as a central node in tumour angiogenesis and support the use of miR-192 in an anti-angiogenesis therapy.
