Elsevier

Experimental Cell Research

Volume 283, Issue 1, 1 February 2003, Pages 51-66
Experimental Cell Research

Regular article
Apoptosis by Par-4 in cancer and neurodegenerative diseases

https://doi.org/10.1016/S0014-4827(02)00016-2Get rights and content

Abstract

Prostate apoptosis response-4 (par-4) is a pro-apoptotic gene identified in prostate cancer cells undergoing apoptosis. Par-4 protein, which contains a leucine zipper domain at the carboxy-terminus, functions as a transcriptional repressor in the nucleus. Par-4 selectively induces apoptosis in androgen-independent prostate cancer cells and Ras-transformed cells but not in androgen-dependent prostate cancer cells or normal cells. Cells that are resistant to apoptosis by Par-4 alone, however, are greatly sensitized by Par-4 to the action of other pro-apoptotic insults such as growth factor withdrawal, tumor necrosis factor, ionizing radiation, intracellular calcium elevation, or those involved in neurodegenerative diseases such as Alzheimer’s, Parkinson’s, Huntington’s, and stroke. Apoptosis induction by Par-4 involves a complex mechanism that requires activation of the Fas death receptor signaling pathway and coparallel inhibition of cell survival NF-κB transcription activity. The unique ability of Par-4 to induce apoptosis in cancer cells but not normal cells and the ability of Par-4 antisense or dominant-negative mutant to abrogate apoptosis in neurodegenerative disease paradigms makes it an appealing candidate for molecular therapy of cancer and neuronal diseases.

Introduction

Physiological cell death in animals, especially in development and in the immune system, occurs by the process of apoptosis. It allows the complete elimination of dying cells without causing an inflammatory response [1], [2]. The key defining features of apoptosis are the activation of a series of cysteine aspartyl proteases or caspases, the central engines of apoptosis that orchestrate cell death by cleaving a variety of intracellular substrates and triggering cell demise. They are synthesized as inactive zymogens and are activated by proteolytic cleavage, typically through the action of upstream caspases. Caspase activation is followed by chromatin condensation and the display of phosphatidylserine on the cell surface that marks the cell for phagocytosis by specialized macrophage or neighboring cells, thus avoiding an inflammatory response [3]. Other typical features of apoptosis include cytoplasmic shrinkage, zeiosis, and the formation of apoptotic bodies with nuclear fragments. The underlying death process is designated apoptosis to delineate it clearly from other death programs such as accidental necrosis, apoptosis-like programmed cell death (PCD), and necrosis-like PCD [4].

Two general pathways are thought to be responsible for activation of the caspase cascades. One such pathway is mediated by transmembrane death receptors of the CD95 (Apo-1 or Fas)/TRAIL/tumor-necrosis factor (TNF) receptor 1 family, whose ligation triggers recruitment and assembly of multiprotein complexes to activate the upstream caspase 8 [5]. The other principal death-signaling pathway involves the mitochondria, which act in response to multiple death insults by releasing cytochrome c into the cytosol. Once released, cytochrome c will induce the assembly of an intracellular apoptosome complex that recruits caspase 9 via the adaptor protein Apaf-1 [6]. Activation of caspase 8 or caspase 9 triggers the activation of effector caspases, such as caspase 3, that are involved in survival substrate degradation and nucleosomal DNA fragmentation [7]. The apoptotic pathways are counteracted by survival signaling pathways, which may act by stabilizing the mitochondrial function and integrity and suppressing release of cytochrome c or by interfering with the assembly of the death receptor complexes and inhibiting upstream caspases [8].

Apoptosis is a critical process that evolved to regulate development and immunity and to protect multicellular organisms from the accumulation of damaged cells. Apoptosis is achieved through complex mechanisms that should be tightly regulated because defects in the suppression of programmed cell death can result in an uncontrolled loss of essential cells, giving rise to diverse diseases like neurodegenerative disorders, AIDS, ischemia, and repercussion injury. On the other hand, accumulation of cells harboring serious mutation or unwanted traits by inhibition of apoptosis leads to cancer and autoimmune diseases [9].

Paradoxically, increased cell proliferation driven by activation of oncoproteins (such as Myc, E1A, and E2F) or inactivation of tumor-suppressor proteins (such as retinoblastoma protein) is often associated with accelerated apoptosis. Thus, the coupling between cell division and cell death is thought to act as a barrier that cells must overcome for cancer initiation and progression. This may be the underlying reason why cancer cells often show a high expression of anti-apoptotic proteins such as Bcl-2, Bcl-xL, survivin, or Bcr-Abl along with inactivation of pro-apoptotic tumor-suppressor proteins p53, p19arf, or PTEN that control apoptosis pathways, generating severe defects in the balance between cell division and programmed cell death in cancer settings. The genetic abnormalities that generate defects in apoptotic pathways allow cancer cells to survive. Interestingly, despite the severe disruption of the classic apoptosis pathways, cancer cells retain at least some molecular components necessary for apoptosis [4].

Various chemical, hormonal, and radiation treatments cause irreparable cellular damage that triggers apoptosis in cancer cells. Consequently, the success of cancer treatment depends not only on its ability to induce irreparable cellular damage but also on the ability to respond to the damage by activation of the apoptotic machinery. Mutations in apoptotic pathways may result in resistance to drugs and radiation. Such mutations can be used to predict resistance to different therapeutic approaches and, consequently, serve as new treatment targets [10]. The challenge is to identify and understand the molecular mechanisms involved in tumor progression and to develop anti-cancer therapies that directly attack key survival mechanisms [8].

It is believed that increased apoptosis in one or more populations of neurons is behind the development of neurodegenerative diseases such as Alzheimer’s, Parkinson’s, Huntington’s, and stroke. Studying apoptosis mechanisms in neurons is just as challenging as in other cell types and organs. But contrary to the goal of dissecting these mechanisms in the development of malignancies, in neurons apoptosis inhibitory pathways are sought. Neurons are long-lived cells that do not undergo active regeneration. While apoptosis is a natural process that is required for normal development of the nervous system, its reactivation later in life is pathological. In the nervous system, different neurological disorders arise from degeneration and death of neurons. Indeed, it is suggested that even when apoptosis is activated in neurons, it is counteracted by responses that slow or reverse this process. Neurotrophic factors have been identified that can protect neurons by activation of survival proteins such as NF-κB [11].

Prostate apoptosis response-4, Par-4, a pro-apoptotic protein, was found to play a critical role in a number of cancer and neurodegenerative disease paradigms. While its pro-apoptotic role in cancer cells should be enhanced, approaches to inhibit Par-4 expression or function must be explored in neurons. This review discusses the identification, characterization, and mechanism of action of Par-4 in various disease paradigms and its potential in molecular therapeutics.

Section snippets

Identification and expression of Par-4

Prostate cancer is conventionally treated by androgen ablation, which shows an initial response in about 80% of cases. Unfortunately, only the androgen-dependent cancer cells are affected by this treatment while androgen-independent cancer cells, which may constitute part of the tumor, are not eliminated, leading to relapse of the disease. Par-4 was first identified in an experiment performed to find common apoptotic genes induced in response to apoptotic insults in androgen-dependent and

Structure–function analysis of Par-4

Rat Par-4 is a 332-amino-acid protein (Fig. 2). It has an apparent molecular weight of about 40 kDa on SDS–PAGE. Sequence analysis of the Par-4 sequence revealed a number of interesting sites and domains. One of the most interesting domains of Par-4 is the leucine zipper domain that spans the region between amino acids 292 and 332 (Fig. 2). The primary sequence of a leucine zipper is a roughly 42-residue stretch having a repeated heptad (A-B-C-D-E-F-G-) with nonpolar residues predominating at

Functional role of Par-4

Although the exact physiological role of endogenous Par-4 protein is not known, several functions are uncovered by the interesting array of molecules that Par-4 affects and/or interacts with. All of the partners of Par-4 identified to date are involved with cell survival, transformation, or apoptosis. Human Par-4 was first identified as a binding partner and inhibitor of WT1 and the aPKC [16], [17]. Par-4 also binds and enhances the apoptotic function of DAP-like kinase (Dlk/Zip kinase) [24] (

Mechanism of apoptosis by Par-4

The pro-apoptotic role of Par-4 is apparent from its effect when overexpressed in different cell lines, its effects in cancer and neurodegenerative disease paradigm, and the interesting array of its partner proteins. Consistently, multiple mechanisms are involved in its ability to induce apoptosis (Fig. 4).

Interaction with WT1 may be involved in the inhibition of growth arrest and inhibition of Bcl-2, which is a potent anti-apoptotic protein [16], [29], [48]. Down-regulation of Bcl-2 allows

Potential for Par-4 in molecular therapeutics

Gene therapy has been used to induce apoptotic programs with various degrees of success. The first approach was directed to restore normal p53 functions in cancer cells. Although the initial results have been interesting, refinement of the vectors and delivery concepts is needed. Phase I clinical and pharmacokinetic studies with Bcl-2 antisense oligonucleotide (which effectively degrades messenger RNA) in patients with non-Hodgkin’s lymphoma was well tolerated. Bcl-2 protein level was reduced

Acknowledgements

This work was supported by NIH research grants CA60872 and CA84511. We thank Sushma Gurumurthy for a critical reading of the review.

References (116)

  • S.B. Lee et al.

    Wilms tumor and the WT1 gene

    Exp. Cell Res.

    (2001)
  • N.A. Bourbon et al.

    Ceramide-induced inhibition of Akt is mediated through protein kinase CzetaImplications for growth arrest

    J. Biol. Chem.

    (2002)
  • M. Hanada et al.

    bcl-2 gene hypomethylation and high-level expression in B-cell chronic lymphocytic leukemia

    Blood

    (1993)
  • A. Nalca et al.

    Oncogenic Ras sensitizes cells to apoptosis by Par-4

    J. Biol. Chem.

    (1999)
  • D.J. Selkoe

    Amyloid beta-protein and the genetics of Alzheimer’s disease

    J. Biol. Chem.

    (1996)
  • Q. Guo et al.

    Prostate apoptosis response-4 enhances secretion of amyloid beta peptide 142 in human neuroblastoma IMR-32 cells by a caspase-dependent pathway

    J. Biol. Chem.

    (2001)
  • J. Xie et al.

    Aberrant induction of Par-4 is involved in apoptosis of hippocampal neurons in presenilin-1 M146V mutant knock-in mice

    Brain Res.

    (2001)
  • A. Nath et al.

    Neurobiological aspects of human immunodeficiency virus infectionNeurotoxic mechanisms

    Prog. Neurobiol.

    (1998)
  • A.I. Dayton et al.

    The trans-activator gene of the human T cell lymphotropic virus type III is required for replication

    Cell

    (1986)
  • I.l. Kruman et al.

    HIV-1 protein Tat induces apoptosis of hippocampal neurons by a mechanism involving caspase activation, calcium overload, and oxidative stress

    Exp. Neurol.

    (1998)
  • W. Duan et al.

    Participation of par-4 in the degeneration of striatal neurons induced by metabolic compromise with 3-nitropropionic acid

    Exp. Neurol.

    (2000)
  • Q. Guo et al.

    Par-4 is a synaptic protein that regulates neurite outgrowth by altering calcium homeostasis and transcription factor AP-1 activation

    Brain Res.

    (2001)
  • R. Sen et al.

    Multiple nuclear factors interact with the immunoglobulin enhancer sequences

    Cell

    (1986)
  • J. Anrather et al.

    Regulation of NF-kappaB RelA phosphorylation and transcriptional activity by p21(ras) and protein kinase Czeta in primary endothelial cells

    J. Biol. Chem.

    (1999)
  • H. Sakurai et al.

    IkappaB kinases phosphorylate NF-kappaB p65 subunit on serine 536 in the transactivation domain

    J. Biol. Chem.

    (1999)
  • T.S. Finco et al.

    Oncogenic Ha-Ras-induced signaling activates NF-kappaB transcriptional activity, which is required for cellular transformation

    J. Biol. Chem.

    (1997)
  • N.D. Perkins

    The Rel/NF-kappa B familyFriend and foe

    Trends Biochem. Sci.

    (2000)
  • M.E. Peter et al.

    Mechanisms of CD95 (APO-1/Fas)-mediated apoptosis

    Curr. Opin. Immunol.

    (1998)
  • A. de Thonel et al.

    Role of protein kinase C zeta isoform in Fas resistance of immature myeloid KG1a leukemic cells

    Blood

    (2001)
  • A. Galan et al.

    Stimulation of p38 mitogen-activated protein kinase is an early regulatory event for the cadmium-induced apoptosis in human promonocytic cells

    J. Biol. Chem.

    (2000)
  • P.H. Krammer

    CD95’s deadly mission in the immune system

    Nature

    (2000)
  • M. Leist et al.

    Four deaths and a funeralFrom caspases to alternative mechanisms

    Nat. Rev. Mol. Cell. Biol.

    (2001)
  • A. Ashkenazi et al.

    Death receptorsSignaling and modulation

    Science

    (1998)
  • N.A. Thornberry et al.

    CaspasesEnemies within

    Science

    (1998)
  • G.I. Evan et al.

    Proliferation, cell cycle and apoptosis in cancer

    Nature

    (2001)
  • C.B. Thompson

    Apoptosis in the pathogenesis and treatment of disease

    Science

    (1995)
  • J. Sjostrom et al.

    How apoptosis is regulated, and what goes wrong in cancer

    Br. Med. J.

    (2001)
  • M.P. Mattson et al.

    NF-kappaB in neuronal plasticity and neurodegenerative disorders

    J. Clin. Invest.

    (2001)
  • S.F. Sells et al.

    Commonality of the gene programs induced by effectors of apoptosis in androgen-dependent and -independent prostate cells

    Cell Growth Differ.

    (1994)
  • N. Kyprianou et al.

    Programmed cell death during regression of PC-82 human prostate cancer following androgen ablation

    Cancer Res.

    (1990)
  • J. Connor et al.

    Calcium channel antagonists delay regression of androgen-dependent tissues and suppress gene activity associated with cell death

    Prostate

    (1988)
  • P. Martikainen et al.

    Programmed death of nonproliferating androgen-independent prostatic cancer cells

    Cancer Res.

    (1991)
  • R.W. Johnstone et al.

    A novel repressor, par-4, modulates transcription and growth suppression functions of the Wilms’ tumor suppressor WT1

    Mol. Cell. Biol.

    (1996)
  • E. Austruy et al.

    Characterization of regions of chromosomes 12 and 16 involved in nephroblastoma tumorigenesis

    Genes Chromosomes Cancer

    (1995)
  • E.R. Boghaert et al.

    Immunohistochemical analysis of the proapoptotic protein Par-4 in normal rat tissues

    Cell Growth Differ.

    (1997)
  • K. Dutta et al.

    pH-induced folding of an apoptotic coiled coil

    Protein Sci.

    (2001)
  • D.O. Kogel et al.

    Cloning and characterization of Dlk, a novel serine/threonine kinase that is tightly associated with chromatin and phosphorylates core histones

    Oncogene

    (1998)
  • Q. Guo et al.

    Par-4 is a mediator of neuronal degeneration associated with the pathogenesis of Alzheimer disease

    Nat. Med.

    (1998)
  • N. El-Guendy, V.M. Rangnekar, Nuclear translocation of Par-4 is essential for inhibition of RelA in a ζPKC dependent...
  • S. Cheema, V.M. Rangnekar, A.M. Tari, G. Lopez-Berestein, Par-4 transcriptionally regulates Bcl-2 through a WT1 binding...
  • Cited by (0)

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