RGD Reference Report - Calnuc, an EF-hand Ca(2+)-binding protein, is stored and processed in the Golgi and secreted by the constitutive-like pathway in AtT20 cells. - Rat Genome Database

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Calnuc, an EF-hand Ca(2+)-binding protein, is stored and processed in the Golgi and secreted by the constitutive-like pathway in AtT20 cells.

Authors: Lavoie, C  Meerloo, T  Lin, P  Farquhar, MG 
Citation: Lavoie C, etal., Mol Endocrinol. 2002 Nov;16(11):2462-74.
RGD ID: 9831143
Pubmed: PMID:12403836   (View Abstract at PubMed)
DOI: DOI:10.1210/me.2002-0079   (Journal Full-text)

Calnuc is an ubiquitous, EF-hand Ca(2+) binding protein found in the cytoplasm where it binds to Galphai3, in the Golgi lumen where it constitutes a Ca(2+) storage pool, and secreted outside the cell. Here we investigated the pathway of secretion of calnuc in AtT20 cells. We found by pulse-chase experiments that calnuc is synthesized in the endoplasmic reticulum, transported to the Golgi where it remains greater than 12 h and undergoes posttranslational modification (O-glycosylation and sulfation) followed by secretion into the culture medium. We examined if calnuc is secreted by the constitutive or regulated secretory pathway in AtT20 cells. By immunofluorescence and immunogold labeling, endogenous calnuc is found in immature secretion granules (ISG) but not mature regulated secretory granules (RSG), whereas overexpressed calnuc-green fluorescent protein (GFP) is found in both ISG and RSG, where it colocalizes with ACTH. Neither calnuc nor calnuc-GFP are released by the regulated secretory pathway, suggesting that endogenous calnuc and calnuc-GFP are progressively removed from ISG and RSG during granule maturation. We conclude that calnuc is secreted via the constitutive-like pathway and represents a useful endogenous marker for this pathway in AtT20 cells. Together, these observations indicate that calnuc has a unique itinerary as it is retained in the Golgi and is then constitutively secreted extracellularly where it may influence cell behavior via its Ca(2+)-binding properties.

Gene Ontology Annotations    Click to see Annotation Detail View

Cellular Component
TermQualifierEvidenceWithReferenceNotesSourceOriginal Reference(s)
extracellular space  IDA 9831143 RGD 

Objects Annotated

Genes (Rattus norvegicus)
Nucb1  (nucleobindin 1)


Additional Information