Nonsecreted Insulin-like Growth Factor Binding Protein-3 (Igfbp-3) Can Induce Apoptosis in Human Prostate Cancer Cells by Igf-independent Mechanisms Without Being Concentrated in the Nucleus.
From: Diabetes Branch, NIDDK, National Institutes of Health, Bethesda, Maryland 20892, USA.
The Journal of biological chemistry
- Publish Date: Aug 2006
- ISSN: 0021-9258
- Volume: 281
- Issue: 34
- Pages: 24588-601
- Medium: Print
- Language: English
- Citation (JAMA): Bhattacharyya Nisan, Pechhold Klaus, Shahjee Hanief, et al. Nonsecreted Insulin-like Growth Factor Binding Protein-3 (Igfbp-3) Can Induce Apoptosis in Human Prostate Cancer Cells by Igf-independent Mechanisms Without Being Concentrated in the Nucleus.. J. Biol. Chem. Aug 2006;281:24588-601
Abstract
Insulin-like growth factor binding protein-3 (IGFBP-3), a secreted protein, has the intrinsic ability to induce apoptosis directly without binding insulin-like growth factors. Previous studies suggested that IGFBP-3 must be secreted to exert its biological functions. IGFBP-3 contains a nuclear localization signal (NLS), and exogenous IGFBP-3 is translocated into the nucleus, suggesting that both secretion and nuclear localization may play important roles in IGFBP-3 action. To address these questions, we fused yellow fluorescent protein (YFP) to mature IGFBP-3 lacking its signal peptide so that it would remain intracellular and mutated the C-terminal NLS of IGFBP-3, (228)KGRKR(232), to MDGEA. Following transfection of PC-3 human prostate cancer cells with these constructs, Western blots indicated that YFP-IGFBP-3 lacking a signal peptide was cell-associated and not present in the extracellular media. Moreover, the fusion protein was not N-glycosylated, indicating that it had not entered the secretory pathway. Confocal imaging showed that intracellular YFP-MDGEA-IGFBP-3 was predominantly cytoplasmic. Transient transfection of nonsecreted YFP-wild-type IGFBP-3 decreased cell viability, as assessed by staining with annexin V followed by flow cytometry. Induction of cell death was caspase-dependent, indicative of apoptosis. Apoptosis also was induced by the nonsecreted NLS mutant (YFP-MDGEA-IGFBP-3) alone and when the IGF-binding site also had been mutated. These results indicate that IGFBP-3 can induce apoptosis in an IGF-independent manner without being secreted or concentrated in the nucleus.
Mesh Headings (Keywords): Apoptosis, Binding Sites, Cell Line, Tumor, Cell Nucleus, Humans, Insulin-Like Growth Factor Binding Protein 3, Insulin-Like Growth Factor I, Insulin-Like Growth Factor II, Male, Prostatic Neoplasms, Protein Binding, Protein Transport
Check for Full Text / PubMed Unique Identifier (PMID): 16793770
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