The Amino-terminal Peptide Of Bax Perturbs Intracellular Ca2+ Homeostasis To Enhance Apoptosis In Prostate Cancer Cells

During apoptosis, proteolytic cleavage of Bax at the amino terminus generates a truncated Bax of ∼18 kDa (p18Bax) and an amino-terminal peptide of ∼3 kDa (p3Bax). Whereas extensive studies have shown that p18Bax behaves like a BH3 protein with enhanced pro-apoptotic function over that of the full-length Bax (p21Bax), little is known about the function of p3Bax in apoptosis. We have previously shown that Bax and Ca2+ play a synergistic role in amplifying apoptosis signaling and that store-operated Ca2+ entry (SOCE) contributes to Bax-mediated apoptosis in prostate cancer cells. Here we test whether p3Bax can contribute to regulation of Ca2+ signaling during apoptosis through use of a membrane-penetrating peptide to facilitate delivery of recombinant p3Bax into NRP-154 cells, a prostate epithelial cell line with tumorigenic capacity. We find that human immunodefficiency virus transactivator of transcription protein (TAT)-p3Bax fusion peptide can enhance thapsigargin-induced apoptosis in NRP-154 cells, elevate SOCE activity, and increase inositol 1,4,5-trisphosphate-sensitive intracellular Ca2+ stores. Our data indicates that p3Bax can modulate the entry of extracellular Ca2+ and thus regulate the amplification of apoptosis in prostate cancer cells.

Download Full-text

AKT-Independent Protection of Prostate Cancer Cells from Apoptosis Mediated through Complex Formation between the Androgen Receptor and FKHR

Molecular and Cellular Biology ◽

10.1128/mcb.23.1.104-118.2003 ◽

2003 ◽

Vol 23 (1) ◽

pp. 104-118 ◽

Cited By ~ 109

Author(s):

Pengfei Li ◽

Heehyoung Lee ◽

Shaodong Guo ◽

Terry G. Unterman ◽

Guido Jenster ◽

...

Keyword(s):

Prostate Cancer ◽

Androgen Receptor ◽

Cell Survival ◽

Cancer Cells ◽

Cancer Cell ◽

Cell Apoptosis ◽

Prostate Cancer Cell ◽

Transcriptional Analysis ◽

Prostate Cancer Cells ◽

Amino Terminal

ABSTRACT Recent studies suggested that the protection of cell apoptosis by AKT involves phosphorylation and inhibition of FKHR and related FOXO forkhead transcription factors and that androgens provide an AKT-independent cell survival signal in prostate cancer cells. Here, we report receptor-dependent repression of FKHR function by androgens in prostate cancer cells. Transcriptional analysis demonstrated that activation of the androgen receptor caused an inhibition of both wild-type FKHR and a mutant in which all three known AKT sites were mutated to alanines, showing that the repression is AKT independent. In vivo and in vitro coprecipitation studies demonstrated that the repression is mediated through protein-protein interaction between FKHR and the androgen receptor. Mapping analysis localized the interacting domains to the carboxyl terminus between amino acids 350 and 655 of FKHR and to the amino-terminal A/B region and the ligand binding domain of the receptor. Further analysis demonstrated that the activated androgen receptor blocked FKHR's DNA binding activity and impaired its ability to induce Fas ligand expression and prostate cancer cell apoptosis and cell cycle arrest. These studies identify a new mechanism for androgen-mediated prostate cancer cell survival that appears to be independent of the activity of the receptor on androgen response element-mediated transcription and establish FKHR and related FOXO forkhead proteins as important nuclear targets for both AKT-dependent and -independent survival signals in prostate cancer cells.

Download Full-text