Resistance to caspase-dependent, hypoxia-induced apoptosis is not hypoxia-inducible factor-1 alpha mediated in prostate carcinoma cells

BACKGROUND

Hypoxia occurs in association with cancer development, the result being a more aggressive and metastatic cancer phenotype. Hypoxia, which activates hypoxia-inducible factor-1 alpha (HIF-1alpha), is associated with a number of cellular changes including increased apoptotic resistance. The authors hypothesized that HIF-1alpha is central to the cell's ability to resist apoptosis induced during the hypoxia selection process.

METHODS

PWR-1E, LNCaP, LNCaP-HOF, PC-3, and DU-145 cells were cultured in normoxic and hypoxic conditions. Apoptosis was assessed by propidium iodide DNA staining. Cleavage of specific substrates was used to assess caspase activity and Western blotting was used to assess mitochondrial release of cytochrome c and second mitochondria-derived activator caspase (SMAC)/Diablo. A dominant negative HIF-1alpha construct was transfected into the PC-3 and LNCaP cells to block HIF-1alpha activity.

RESULTS

PC-3 and DU-145 were resistant to apoptosis induced by exposure to hypoxia, but the PWR-1E and LNCaP cells were susceptible. This induction of apoptosis in the LNCaP cells was caspase dependent but independent of cytochrome c release. Blocking the activity of HIF-1alpha had no effect on increased apoptotic susceptibility in the PC-3 cells. LNCaP-HOF cells, which were resistant to hypoxia-induced apoptosis, showed no increase in HIF-1alpha expression or activity.

CONCLUSIONS

Apoptotic resistance is already established in cells that survive a hypoxic insult and whereas increased HIF-1alpha activity may be essential for the development of a more aggressive cancer phenotype, it may not be responsible for the initial selection of an apoptotic resistance phenotype.

Hypoxia inhibits human bladder smooth muscle cell proliferation: a potential mechanism of bladder dysfunction

AIMS

Recent animal studies have suggested that bladder outflow obstruction causes bladder wall hypoxia during both the filling and the voiding phases of the micturition cycle. We have previously demonstrated that mechanical deformation of human detrusor leads to smooth muscle (SM) cell hypertrophy and hyperplasia, which may then contribute to hypoxia in the dysfunctional bladder. We hypothesise that the detrusor's response to a hypoxic environment contributes to bladder dysfunction. The aim of this study was to evaluate the effect of hypoxia on detrusor cell survival and growth.

METHODS

Normal human detrusor muscle was obtained at radical cystectomy and primary cultures were established. Cells were then cultured in the presence of 1% oxygen in a hypoxic chamber for different times. Apoptosis was assessed by propidium iodide DNA staining and flow cytometry. Proliferation was assessed by radiolabelled thymidine incorporation. Cell supernatants were retained for growth factor estimation by enzyme linked immuno-sorbent assay (ELISA), and total cell and nuclear extracts were isolated for Western blotting.

RESULTS

SM cells responded to the presence of hypoxia through significant upregulation of survival factors hypoxia inducible factor (HIF 1alpha) and vascular endothelial growth factor (VEGF) in a time-dependent manner. Hypoxia did not induce cell death, but significantly reduced the rate of proliferation over time, associated with an increase in the cell cycle inhibitor p27kip1.

CONCLUSIONS

In an in vitro human detrusor cell culture model, cells demonstrate a resistance to hypoxia-induced apoptosis but proliferation is inhibited. We suggest that the anti-proliferative effects of hypoxia may limit the ability of detrusor cells to respond to, and compensate for, alterations in their environment contributing to bladder dysfunction.

Androgen-mediated resistance to apoptosis

BACKGROUND

Previous studies demonstrate that androgen is capable of exerting a protective effect in the androgen-sensitive human prostate cancer cell line LNCaP. Limited studies, however, have addressed the underlying mechanisms involved, in particular the effects of androgen on both pro- and anti-apoptotic gene expression.

METHODS

We investigated the effects of androgen on apoptotic sensitivity and the expression of the caspases and specific members of the Bcl-2 family in the LNCaP cell line. The effects of androgen on NF-kappaB activation were also investigated by using a gel mobility shift assay.

RESULTS

5alpha-Dihydrotestosterone (5-alphaDHT) conferred resistance to radiation (5 Gy) and etoposide-induced apoptosis in the LNCaP cell line. This finding was associated with a time-dependent decrease in the expression of the caspases and pro-apoptotic Bcl-2 family members. 5-alphaDHT did not confer protection against apoptosis in the LNCaP line transfected with the IkappaB super repressor of NF-kappaB, nor in the androgen insensitive PC-3 and DU-145 cell lines.

CONCLUSION

The ability of 5-alphaDHT to raise the apoptotic threshold in the LNCaP cell line by altering specific pro-apoptotic gene expression suggests that androgen may serve as a general survival signal against diverse pathways that ultimately signal for apoptosis. We hypothesize that NF-kappaB serves as an important mediator in androgen survival signaling.

Effects of cyclic stretch on prostatic cells in culture

PURPOSE

The fundamental process in the development of benign prostatic hyperplasia (BPH) is a loss of homeostasis between cell proliferation and apoptosis. Prostatic smooth muscle cells contract under adrenergic control. The response of a cell to stretch may have a role in the pathogenesis of BPH.

MATERIALS AND METHODS

Monolayer cultures of human prostatic stromal and epithelial cell lines were exposed to cyclic stretch for 48 hours.

RESULTS

Cyclic stretch conferred resistance to etoposide induced apoptosis. Underlying this apoptotic resistance was increased expression of the anti-apoptotic Bcl-2 family of proteins. As measured by thymidine incorporation, the rate of proliferation also increased in benign epithelial cells under cyclic stretch conditions. Furthermore, an increase in the production of platelet-derived growth factor by stromal cells and transforming growth factor-beta by epithelial cells occurred under such conditions.

CONCLUSIONS

The observed changes in proliferation and apoptosis may contribute to the understanding of BPH, ultimately leading to therapeutic and preventive applications.

Inhibitors of apoptosis proteins in prostate cancer cell lines

BACKGROUND

The caspases are the central executioners of apoptosis. The inhibitors of apoptosis proteins (IAPs) are a family of recently described caspase inhibitors. We hypothesised that tumor resistance to apoptosis could be due in part to IAP expression.

METHODS

The expression of NAIP, cIAP-1, cIAP-2, XIAP, and survivin was investigated in the prostate cancer cell lines LNCaP, PC3, and DU145. RNase protection assays and Western blotting were used to assess RNA and protein expression. Apoptotic susceptibility was determined using etoposide and assessed by propidium iodide (PI) DNA incorporation using flow cytometry.

RESULTS

DU145 and PC3 cells were more resistant to apoptosis than LNCaP cells. All the IAPs were identified in the cell lines with variation in IAP expression between different cell types. Immunohistochemistry demonstrated cIAP-1 expression in PC3 cells was nuclear, while the expression of cIAP-2 and XIAP was perinuclear. Growing LNCaP cells in charcoal-stripped or androgen-supplemented medium resulted in no alteration in IAP expression.

CONCLUSIONS

This study characterises the expression of IAP in three of the most commonly used prostate cancer cells. IAP may make an important contribution to apoptotic resistance in patients with prostate cancer.