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Insulin-like growth factor-binding protein-3 is partially responsible for high-serum-induced apoptosis in PC-3
Abstract:
Cells are known to undergo apoptosis when cultured in high serum concentrations. However, the serum factors responsible for this induction of apoptosis have not been identified. The IGF-binding protein-3 (IGFBP-3), a negative growth regulator, is found at concentrations of 5 microgram/ml in serum. We have recently demonstrated that IGFBP-3 induces apoptosis in PC-3 cells, a prostate cancer cell line, at a concentration of 500 ng/ml. In this communication, we demonstrate the role of IGFBP-3 as one of the apoptosis-inducing agents in high serum concentrations. Treatment of PC-3 cells with increasing concentrations (40% to 90%) of intact human serum (HS) resulted in a dose-dependent decrease in cell growth. Valinomycin, an ionophore, was used as a positive control to measure the induction of apoptosis by serum treatment in PC-3 cells. Treatment with 90% serum showed significant suppression of growth (P<0.001) compared with the effect of 10% serum. Treatment with increasing concentrations of HS (40% to 90%) resulted in a dose-dependent increase in apoptosis. Treatment with 90% HS showed a 10-fold increase in apoptotic index compared with cells treated with 10% HS. Treatment of PC-3 cells with IGFs and IGFBP-3-depleted 90% human sera (depleted serum=DS) demonstrated significantly lower levels of apoptosis (50% reduction in the effect of 90% HS) suggesting a role of IGFBP-3 in inducing apoptosis in high serum concentration. Furthermore, treatment with DS supplemented with recombinant IGFBP-3 (500 ng/ml) brought the apoptotic index down close to the level of apoptosis induced by 90% intact serum treatment (P<0.001). However, DS supplemented with physiological concentrations of IGFs (500 ng/ml) showed only partial recovery of cell survival demonstrated by 90% DS. This data indicates that IGFBP-3 is one of the factors in serum that is responsible for high-serum-induced apoptosis.
Insights
High serum concentrations induce apoptosis in cells. Insulin-like growth factor-binding protein-3 (IGFBP-3) in serum is identified as a key factor responsible for this apoptosis induction in prostate cancer cells.
Area of Science:
- Cell Biology
- Molecular Biology
- Cancer Research
Background:
- Cells undergo apoptosis (programmed cell death) when cultured in high serum concentrations.
- The specific serum factors inducing apoptosis in high concentrations remain unidentified.
- Insulin-like growth factor-binding protein-3 (IGFBP-3) is a known negative growth regulator present in serum.
Purpose of the Study:
- To identify the serum factors responsible for high-serum-induced apoptosis.
- To demonstrate the role of IGFBP-3 as an apoptosis-inducing agent in high serum concentrations.
- To investigate the effect of IGFBP-3 on apoptosis in PC-3 prostate cancer cells.
Main Methods:
- PC-3 cells were treated with increasing concentrations of human serum (HS) (40%–90%).
- Apoptosis induction was measured using valinomycin as a positive control.
- Cells were treated with IGFs and IGFBP-3-depleted human serum (DS), with and without recombinant IGFBP-3 or IGFs.
Main Results:
- High serum concentrations (up to 90%) significantly suppressed PC-3 cell growth and increased apoptosis in a dose-dependent manner.
- Treatment with 90% HS showed a 10-fold increase in apoptotic index compared to 10% HS.
- IGFBP-3-depleted serum significantly reduced apoptosis, which was restored by adding recombinant IGFBP-3, but not IGFs alone.
Conclusions:
- IGFBP-3 is identified as a significant factor in high-serum-induced apoptosis in PC-3 cells.
- This finding elucidates a mechanism by which high serum concentrations trigger programmed cell death.
- The study highlights IGFBP-3's role in regulating cell survival in the context of serum concentration.