Disease relevance of Crhsp-28

• Internal amino acid sequences of purified CRHSP-28 were obtained following trypsin digestion and found to match with >95% identity the predicted amino acid sequence of a novel cDNA recently identified as being highly expressed in human breast carcinomas [1].

High impact information on Crhsp-28

• Identification of annexin VI as a Ca2+-sensitive CRHSP-28-binding protein in pancreatic acinar cells [2].
• Stimulation of cells for 5 min with the secretagogue cholecystokinin enhanced the colocalization of CRHSP-28 and annexin VI within regions of acini immediately below the apical plasma membrane [2].
• In the present study, the Ca(2+)-sensitive phospholipid-binding protein annexin VI was purified from rat pancreas as a CRHSP-28-binding protein [2].
• The interaction between CRHSP-28 and annexin VI was demonstrated by coimmunoprecipitation and gel-overlay assays and was shown to require low micromolar levels of free Ca(2+), indicating these molecules likely interact under physiological conditions [2].
• CRHSP-28 is a member of the tumor protein D52 protein family that was recently shown to regulate Ca(2+)-stimulated secretory activity in streptolysin-O-permeabilized acinar cells (Thomas, D. H., Taft, W. B., Kaspar, K. M., and Groblewski, G. E. (2001) J. Biol. Chem. 276, 28866-28872) [2].

Biological context of Crhsp-28

• Dietary and hormonal stimulation of rat exocrine pancreatic function regulates CRHSP-28 phosphorylation in vivo [3].
• The CCK-8-induced accumulation of CRHSP-28 in subapical regions of acini was not altered by inhibition of apical endocytosis with the actin filament-disrupting agent latrunculin B [4].

Anatomical context of Crhsp-28

• Tissue fractionation revealed that CRHSP-28 is a peripheral membrane protein that is highly enriched in smooth microsomal fractions of pancreas [2].
• Collectively, the Ca(2+)-dependent binding of CRHSP-28 and annexin VI, together with their colocalization in the apical cytoplasm, is consistent with a role for these molecules in acinar cell membrane trafficking events that are essential for digestive enzyme secretion [2].
• Further, the content of CRHSP-28 in microsomes was significantly reduced in pancreatic tissue obtained from rats that had been infused with a secretory dose of cholecystokinin for 40 min, demonstrating that secretagogue stimulation transiently alters the association of CRHSP-28 with membranes in cells [2].
• Sparse, but significant, CRHSP-28 immunoreactivity was also observed along the limiting membrane of zymogen granules [4].
• Dual-immunofluorescence microscopy demonstrated an endosomal localization of CRHSP-28 that strongly overlapped with early endosomal antigen-1 (EEA-1) on vesicular structures throughout the apical cytoplasm but showed only minimal overlap with the transferrin receptor, which is present in basolaterally derived endosomes [4].

Associations of Crhsp-28 with chemical compounds

• Interestingly, treatment of lobules with brefeldin A reversibly disrupted the vesicular localization of CRHSP-28 and EEA-1 within the apical cytoplasm [4].
• CRHSP-28 phosphorylation was contingent on elevated cellular Ca2+ because it was maximally stimulated by Ca2+ ionophore, but unchanged after protein kinase C, cAMP or cyclic guanosine monophosphate activation [3].
• CRHSP-28 is predicted to be extremely hydrophilic, is phosphorylated entirely on serine residues, and bears little homology to any known proteins [1].

Other interactions of Crhsp-28

• Intravenous infusion of rats with a secretory concentration of the CCK analog, caerulein, stimulated CRHSP-28 phosphorylation by 100% over control (P < 0.01) within 15 min of dosing [3].

Analytical, diagnostic and therapeutic context of Crhsp-28

• Immunofluorescence microscopy confirmed a dual localization of CRHSP-28 and annexin VI, which appeared in a punctate pattern in the supranuclear and apical cytoplasm of acini [2].
• Immunoelectron microscopy confirmed that CRHSP-28 is associated with the limiting membrane of irregularly shaped vesicular structures of low electron density in the apical cytoplasm that are positive for EEA-1 staining [4].
• In the present study, isoelectric focusing and immunoblotting were used to characterize CRHSP-28 phosphorylation in isolated rat acinar cells and also after hormonal and dietary stimulation of rat pancreas in vivo [3].

References