title: The Siva-1 putative amphipathic helical region (SAH) is sufficient to bind to BCL-XL and sensitize cells to UV radiation induced apoptosis.
abstract: The human Siva gene is localized to chromosome 14q32-33 and gives rise to the full-length predominant form, Siva-1 and a minor alternate form, Siva-2 that appears to lack the proapoptotic properties of Siva-1. Our recent work has shown that the missing region in Siva-2 encodes a unique twenty amino acid putative amphipathic helical region (SAH, residues 36-55 in Siva-1). Despite the fact that Siva-1 does not belong to the BCL-2 family, it specifically interacts with the anti-apoptotic protein BCL-XL and sensitizes MCF7 breast cancer cells expressing BCL-XL to UV radiation induced apoptosis. Deletion mutagenesis has mapped the necessary region to the SAH in Siva-1. In this paper we demonstrate that the SAH region in Siva-1 is sufficient to specifically interact with the anti-apoptotic members of the BCL2 family such as BCL-XL and BCL-2 but not its apoptotic member BAX. Using transient transfections and direct microinjection of synthetic SAH peptides, we also demonstrate that the SAH region is sufficient to inhibit the BCL-XL mediated cell survival and render MDA-MB-231 and MCF7 breast cancer cells expressing BCL-XL highly susceptible to UV radiation induced apoptosis. The underlying mechanism of action of SAH mediated inhibition of BCL-XL (and/or BCL2) cell survival appears to be due to loss of mitochondrial integrity as reflected in enhanced cytochrome c release leading to the activation of caspase 9 and finally caspase 3.
authors.affiliation: Department of Microbiology & Immunology, University of Illinois at Chicago, 835 S. Wolcott Ave., M/C790, Chicago, IL 60612, USA.
authors.forename: F
authors.initials: F
authors.lastname: Chu
authors.forename: A
authors.initials: A
authors.lastname: Borthakur
authors.forename: X
authors.initials: X
authors.lastname: Sun
authors.forename: J
authors.initials: J
authors.lastname: Barkinge
authors.forename: R
authors.initials: R
authors.lastname: Gudi
authors.forename: S
authors.initials: S
authors.lastname: Hawkins
authors.forename: K V S
authors.initials: KV
authors.lastname: Prasad
mesh_terms: D000199:Actins / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D017209:Apoptosis; D051017:Apoptosis Regulatory Proteins; D019556:COS Cells; D002352:Carrier Proteins / Q000737:chemistry*; D053148:Caspase 3; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism; D045744:Cell Line, Tumor; D045304:Cytochromes c / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D017353:Gene Deletion; D005822:Genetic Vectors; D005982:Glutathione Transferase / Q000378:metabolism; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D051379:Mice; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D008928:Mitochondria / Q000473:pathology; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000737:chemistry* / Q000378:metabolism; D013997:Time Factors; D014466:Ultraviolet Rays; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein
chemical_list: D000199:Actins; D051017:Apoptosis Regulatory Proteins; C494826:BAX protein, human; C494811:BCL2L1 protein, human; C494827:Bax protein, mouse; C494812:Bcl2l1 protein, mouse; D002352:Carrier Proteins; D047908:Intracellular Signaling Peptides and Proteins; D010455:Peptides; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; C106549:SIVA1 protein, human; C484569:Siva protein, mouse; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein; D045304:Cytochromes c; D005982:Glutathione Transferase; C505407:CASP3 protein, human; C506433:CASP9 protein, human; C505409:Casp3 protein, mouse; C506434:Casp9 protein, mouse; D053148:Caspase 3; D053453:Caspase 9; D020169:Caspases