title: Interaction of insulin-like growth factor-binding protein-3 and BAX in mitochondria promotes male germ cell apoptosis.
abstract: Germ cell apoptosis is crucial for spermatogenesis and can be triggered by various stimuli, including intratesticular hormone deprivation. This study proposes a role for insulin-like growth factor binding protein-3 (IGFBP-3) in male germ cell apoptosis. Groups of adult Sprague-Dawley male rats received one of the following treatments for 5 days: (i) daily intratesticular (IT) injections with saline (control); (ii) a single subcutaneous injection of the gonadotropin-releasing hormone antagonist (GnRH-A), acyline, on day 1 and a daily IT injection of saline; (iii) daily IT injection of IGFBP-3; and (iv) a GnRH-A injection on day 1 and a daily IT injection of IGFBP-3. Germ cell apoptosis increased significantly after IGFBP-3 or GnRH-A treatment which was further enhanced by the combined treatment. After co-immunoprecipitation with BAX antibody, IGFBP-3 association with BAX was demonstrated in total and mitochondrial fractions but not in the cytosol of testis extracts. BAX-associated IGFBP-3 expression was increased in mitochondria after treatment compared with control, which was confirmed by an IGFBP-3 enzyme-linked immunosorbent assay. Dot blot studies further validated the BAX-IGFBP-3 binding in vitro. IGFBP-3 as well as BAX induced release of cytochrome c and DIABLO from isolated testicular mitochondria in vitro. IGFBP-3, when combined with an ineffective dose of BAX, triggered release of these proteins from isolated mitochondria at a 4-fold lower dose than IGFBP-3 alone. Our data demonstrate that the IGFBP-3 and BAX interaction activates germ cell apoptosis via the mitochondria-dependent pathway. This represents a novel pathway regulating germ call homeostasis that may have significance for male fertility and testicular disease.
authors.affiliation: Division of Endocrinology, Department of Medicine, Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, Torrance, California 90509-2910, USA.
authors.forename: Yue
authors.initials: Y
authors.lastname: Jia
authors.forename: Kuk-Wha
authors.initials: KW
authors.lastname: Lee
authors.forename: Ronald
authors.initials: R
authors.lastname: Swerdloff
authors.forename: David
authors.initials: D
authors.lastname: Hwang
authors.forename: Laura J
authors.initials: LJ
authors.lastname: Cobb
authors.forename: Amiya
authors.initials: A
authors.lastname: Sinha Hikim
authors.forename: Yan He
authors.initials: YH
authors.lastname: Lue
authors.forename: Pinchas
authors.initials: P
authors.lastname: Cohen
authors.forename: Christina
authors.initials: C
authors.lastname: Wang
mesh_terms: D000818:Animals; D017209:Apoptosis; D051017:Apoptosis Regulatory Proteins; D002352:Carrier Proteins / Q000378:metabolism; D002458:Cell Fractionation; D045304:Cytochromes c / Q000378:metabolism; D004797:Enzyme-Linked Immunosorbent Assay; D007987:Gonadotropin-Releasing Hormone / Q000037:antagonists & inhibitors; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000378:metabolism*; D008297:Male; D051379:Mice; D008928:Mitochondria / Q000378:metabolism*; D024101:Mitochondrial Proteins / Q000378:metabolism; D011485:Protein Binding; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction; D013094:Spermatozoa / Q000166:cytology* / Q000378:metabolism; D013737:Testis / Q000166:cytology; D051028:bcl-2-Associated X Protein / Q000378:metabolism*
chemical_list: D051017:Apoptosis Regulatory Proteins; D002352:Carrier Proteins; C489013:DIABLO protein, rat; D018972:Insulin-Like Growth Factor Binding Protein 3; D024101:Mitochondrial Proteins; D051028:bcl-2-Associated X Protein; D007987:Gonadotropin-Releasing Hormone; D045304:Cytochromes c