title: A mathematical model predicts that calreticulin interacts with the endoplasmic reticulum Ca(2+)-ATPase.
abstract: A robust mathematical model developed from single cell calcium (Ca(2+)) dynamics has enabled us to predict the consequences of over-expression of endoplasmic reticulum-located chaperones. Model predictions concluded that calreticulin interacts with the lumenal domain of the sarcoplasmic and endoplasmic reticulum Ca(2+)-activated ATPase (SERCA) pump, altering pump affinity for Ca(2+) (K(1/2) switches from 247 to 431 nM) and hence generating Ca(2+) oscillations. Expression of calreticulin in the ER generated an average of six transient-decline oscillations during the Ca(2+) recovery phase, upon exposure to maximal levels of the agonist ATP. In contrast, normal cells produced a single Ca(2+) transient with few or no oscillations. By conditioning the model to experimental data, parameters for generation and decay of IP(3) and SERCA pump kinetics were determined. To elucidate the possible source of the oscillatory behavior three possible oscillators, 1) IP(3), 2) IP(3)R, and 3) SERCA pump, were investigated and parameters constrained by experimental data to produce the best candidate. Each of the three oscillators generated very good fits with experimental data. However, converting a normal exponential recovery to a transient-decline oscillator predicted that the SERCA pump is the most likely candidate for calreticulin-mediated Ca(2+) release, highlighting the role of this chaperone as a signal protein within the endoplasmic reticulum.
authors.affiliation: Department of Medical Biochemistry, University of Wales College of Medicine, Heath Park, Cardiff CF14 4XN, United Kingdom.
authors.forename: Helen L
authors.initials: HL
authors.lastname: Baker
authors.forename: Rachel J
authors.initials: RJ
authors.lastname: Errington
authors.forename: Sally C
authors.initials: SC
authors.lastname: Davies
authors.forename: Anthony K
authors.initials: AK
authors.lastname: Campbell
mesh_terms: D002118:Calcium / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000737:chemistry* / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000737:chemistry* / Q000378:metabolism*; D037282:Calreticulin; D004721:Endoplasmic Reticulum / Q000201:enzymology*; D005456:Fluorescent Dyes / Q000494:pharmacology; D016257:Fura-2 / Q000494:pharmacology; D049452:Green Fluorescent Proteins; D006367:HeLa Cells; D006801:Humans; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D007700:Kinetics; D008164:Luminescent Proteins / Q000378:metabolism; D008962:Models, Theoretical; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012261:Ribonucleoproteins / Q000737:chemistry* / Q000378:metabolism*; D012519:Sarcoplasmic Reticulum / Q000201:enzymology; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D015398:Signal Transduction; D013997:Time Factors
chemical_list: D002135:Calcium-Binding Proteins; D037282:Calreticulin; D005456:Fluorescent Dyes; D008164:Luminescent Proteins; D011993:Recombinant Fusion Proteins; D012261:Ribonucleoproteins; D049452:Green Fluorescent Proteins; D015544:Inositol 1,4,5-Trisphosphate; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D000252:Calcium-Transporting ATPases; D002118:Calcium; D016257:Fura-2