C-tail mediated modulation of somatostatin receptor type-4 homo- and heterodimerizations and signaling.
Somatostatin receptors show great diversity in response to agonist mediated receptor-specific homo- and heterodimerizations. Here, using photobleaching-fluorescence resonance energy transfer, immunocytochemistry, western blot and co-immunoprecipitation, we investigated dimerization, trafficking, coupling to adenylyl cyclase and signaling of human somatostatin receptor-4 (hSSTR4) in HEK-293 cells. We also determined the role of the C-tail of hSSTR4 on physiological responses of the cells. wt-hSSTR4 exogenously expressed in HEK-293 cells exhibits constitutive dimerization, inhibits forskolin-stimulated cAMP, and displays agonist dependent changes in pERK1/2 and pERK5 expressions. Upon C-tail deletion, the receptor loses membrane expression and ability to dimerize and inhibition of cAMP and pERK5 however, displays several-fold increases in the expression of pERK1/2. Chimeric hSSTR4 with the C-tail of hSSTR5 functions like wt-hSSTR4, in contrast, with the C-tail of hSSTR1 functions like C-tail deleted hSSTR4. hSSTR4 dimerization and signaling are associated with increased cyclin-dependent-kinase p27(kip1) expression and inhibition of the cell proliferation. We also report heterodimerization between hSSTR4/hSSTR5, but not between hSSTR4/hSSTR1, with significant changes in receptor functions. Taken together, these data define a novel mechanism for the role of hSSTR4 in cell proliferation and modulation of signaling pathways.
Faculty of Pharmaceutical Sciences, Division of Pharmacology and Toxicology, The University of British Columbia, BC, Canada.
Rishi K
RK
Somvanshi
Sabina
S
Billova
Geetanjali
G
Kharmate
Padmesh S
PS
Rajput
Ujendra
U
Kumar
D002460:Cell Line; D049109:Cell Proliferation; D019281:Dimerization; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D031541:Fluorescence Resonance Energy Transfer; D006801:Humans; D050505:Mutant Proteins / Q000378:metabolism / Q000502:physiology; D017434:Protein Structure, Tertiary; D017481:Receptors, Somatostatin / Q000737:chemistry / Q000378:metabolism* / Q000502:physiology; D015398:Signal Transduction
D050505:Mutant Proteins; D017481:Receptors, Somatostatin; C098681:somatostatin receptor subtype-4; C101130:somatostatin receptor type 1; C094573:somatostatin receptor 5; D048049:Extracellular Signal-Regulated MAP Kinases