Agonist-induced up-regulation of human somatostatin receptor type 1 is regulated by beta-arrestin-1 and requires an essential serine residue in the receptor C-tail.
We have previously shown that the human somatostatin receptor type 1 (hSSTR1) does not undergo agonist-induced internalization, but is instead up-regulated at the membrane upon prolonged somatostatin (SST) exposure. The deletion of the carboxyterminal C-tail of the receptor completely abolishes up-regulation. To identify molecular signals that mediate hSSTR1 up-regulation, we created mutant receptors with progressive C-tail deletions. Up-regulation was found to be absent in mutants lacking residues Lys359-Ser360-Arg361. Moreover, point mutation of Ser360 to Ala completely abolished up-regulation. The coexpression of wild type hSSTR1 with V53D, a dominant negative mutant of beta-arrestin-1, completely blocked hSSTR1 up-regulation. Further analysis demonstrated that calcium-calmodulin (CaM) dependent kinases were essential for the SST-induced up-regulation response. Like wild type receptors, all mutants failed to internalize after agonist exposure and were able to inhibit forskolin-stimulated cAMP accumulation. Taking these data together, we suggest that SST-induced hSSTR1 up-regulation is critically dependent upon a specific Lys-Ser-Arg sequence in the C-tail of the receptor, with Ser360 being essential. Up-regulation also requires the participation of CaM protein kinases and interactions with beta-arrestins. In contrast, coupling to adenyl cyclase (AC) and internalization occur independently of molecular signals in the receptor's C-tail.
Ramírez
José L
JL
Fraser Laboratories, Room M3-15, Royal Victoria Hospital, 687 Pine Avenue West, Montreal, Quebec H3A 1A1, Canada.
Watt
Heather L
HL
Rocheville
Magalie
M
Kumar
Ujendra
U
D000262:Adenylyl Cyclases / Q000378:metabolism; D000595:Amino Acid Sequence; D019390:Arrestins / Q000235:genetics / Q000378:metabolism*; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D006801:Humans; D008969:Molecular Sequence Data; D009154:Mutation; D017433:Protein Structure, Secondary; D012333:RNA, Messenger / Q000378:metabolism; D017481:Receptors, Somatostatin / Q000819:agonists* / Q000235:genetics / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D012694:Serine / Q000378:metabolism*; D015854:Up-Regulation; D000071559:beta-Arrestin 1; D000071557:beta-Arrestins
C000605253:ARRB1 protein, human; D019390:Arrestins; D012333:RNA, Messenger; D017481:Receptors, Somatostatin; D011993:Recombinant Fusion Proteins; D000071559:beta-Arrestin 1; D000071557:beta-Arrestins; D012694:Serine; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D000262:Adenylyl Cyclases