Journal
MOLECULAR AND CELLULAR BIOCHEMISTRY
Volume 308, Issue 1-2, Pages 133-139Publisher
SPRINGER
DOI: 10.1007/s11010-007-9621-4
Keywords
GPR56; GPCR; post-translational modification; GPCR proteolytic site; glycosylation; pancreatic cancer; suppressed expression
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Funding
- NCRR NIH HHS [5P20 RR020180] Funding Source: Medline
- NATIONAL CENTER FOR RESEARCH RESOURCES [P20RR020180] Funding Source: NIH RePORTER
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GPR56 is an atypical G protein-coupled receptor (GPCR) with an unusually large N-terminal extracellular region, which contains a long Ser/Thr-rich region forming a mucin-like stalk and due to this feature, GPR56 is thought to be an adhesion GPCR. Recent studies demonstrate that GPR56 plays a role in brain development and tumorigenesis. Here, we report that human GPR56 undergoes GPS (GPCR proteolytic site)-mediated protein cleavage to generate its extracellular domain as an N-terminal fragment (GPR56-N). We also show that GPR56-N is highly glycosylated with N-linked carbohydrate chains. Mouse Gpr56 is ubiquitously expressed in various tissues, with high levels in kidney and pancreas. GPR56 mRNA is detected in diverse human cancer cells including pancreatic cancer cells PANC-1, Capan-1, and MiaCaPa-2. Interestingly, GPR56 protein is either negligible or undetectable in these pancreatic cancer cells, despite the fact that high levels of GPR56 mRNA are observed. Moreover, we have found that protein levels of GPR56 in pancreatic cancer cells were not affected when cells were treated with a proteasome inhibitor MG132. Taken together, these results define the biochemical properties of GPR56 protein, and suggest that the expression of GPR56 protein is suppressed in human pancreatic cancer cells.
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