title: Heat-shock proteins attenuate SERCA inactivation by the anti-apoptotic protein Bcl-2: possible implications for the ER Ca2+-mediated apoptosis.
abstract: We have demonstrated previously that Bcl-2 and Bcl-2Δ21, a C-terminally truncated Bcl-2 sequence, inactivate SERCA (sarcoplasmic/endoplasmic reticulum Ca(2+)-ATPase) 1 in isolated SR (sarcoplasmic reticulum), accompanied by a translocation from CRDs (caveolae-related domains) of the SR. In the present study, we obtained evidence for the interaction of Bcl-2 with SERCA2b in C2C12 myoblasts and HEK (human embryonic kidney)-293 cells. Bcl-2 and SERCA2b co-immunoprecipitated from lysate and microsomal fractions of Bcl-2-overexpressing cells. However, Bcl-2 overexpression resulted only in a slight translocation from the CRDs and no significant SERCA inactivation. In isolated HEK-293 cell microsomes, incubation with Bcl-2Δ21 afforded SERCA2b inactivation and some translocation. HSP (heat-shock protein) 70, HSP90, HSP27 and α-crystallin attenuated Bcl-2Δ21-dependent SERCA2b inactivation. An in vitro mechanistic study with the SERCA1 isoform shows that HSP70 (i) protects SERCA1 from the inactivation by Bcl-2Δ21, (ii) inhibits SERCA1 translocation from CRD fractions, and (iii) prevents the Bcl-2Δ21-dependent loss of FITC labelling. Our data demonstrate that the mechanism of SERCA inactivation by Bcl-2 established in vitro for the SERCA1 isoform can be extended to the main housekeeping SERCA2b isoform, and that functional interactions of SERCA2b and Bcl-2 in the cell may be modulated by HSP70 and other chaperones and stress-regulated proteins.
authors.affiliation: Department of Pharmaceutical Chemistry, University of Kansas, Lawrence, 66047, USA.
authors.forename: Elena S
authors.initials: ES
authors.lastname: Dremina
authors.forename: Victor S
authors.initials: VS
authors.lastname: Sharov
authors.forename: Christian
authors.initials: C
authors.lastname: Schöneich
mesh_terms: D000818:Animals; D017209:Apoptosis; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D018840:HSP70 Heat-Shock Proteins / Q000502:physiology*; D006801:Humans; D066298:In Vitro Techniques; D051379:Mice; D008861:Microsomes / Q000378:metabolism; D018482:Muscle, Skeletal / Q000378:metabolism; D032446:Myoblasts / Q000378:metabolism; D020033:Protein Isoforms / Q000378:metabolism; D021381:Protein Transport; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000502:physiology*; D051381:Rats; D011916:Rats, Inbred F344; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000378:metabolism*
chemical_list: D018840:HSP70 Heat-Shock Proteins; D020033:Protein Isoforms; D019253:Proto-Oncogene Proteins c-bcl-2; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D002118:Calcium