ReviewAloe–emodin modulates PKC isozymes, inhibits proliferation, and induces apoptosis in U-373MG glioma cells
Introduction
Considerable attention has been given recently to the possibility of utilizing aloe–emodin (1,8-dihydroy-3-[hydroxymethyl]-anthraquione) as a chemotherapeutic drug for the treatment of various types of cancers. Aloe–emodin has been reported to have antitumor activity in neuroectodermal tumors [1], neuroblastomas [1], lung carcinoma [2], [3], leukemia cells [4], [5], promyeloleukemic HL-60 cells [6], hepatoma cells [7] and in a Merkel carcinoma cell line [8]. Aloe–emodin's mechanism of action involves apoptosis (programmed cell death) as judged by DNA fragmentation and morphological features [1], [2], [3], modulation of Bcl-2, Bax and Fas family of proteins [2], [7], increased cytochrome c [2], [3], activation of caspase-3 [2], [3], caspase-8 [2] and caspase-9 [2], and increased p53 and p21 proteins [7]. Additionally, aloe–emodin's mechanism of induced apoptosis appears to involve protein kinase C (PKC) [3]. PKC is a family of 11 known isozymes which are found in varying ratios in the cytosolic and membrane fractions of cells, depending on the type of tissue and its physiological state [9]. PKC isozymes can be classified into three groups. Group I includes Ca2+-dependent isozymes: cPKC-α, cPKC-βI, cPKC-βII and cPKC-γ. Isozymes in group II, nPKC-ɛ, nPKC-δ, nPKC-η and nPKC-θ are Ca2+ independent. Group III includes the atypical PKC: aPKC-ί [10], aPKC-ζ and aPKC-μ (protein kinase D) which are phospholipid dependent. PKC regulates cellular functions, metabolism and proliferation by phosphorylating proteins in response to transmembrane signals from hormones, growth factors, neurotransmitters and pharmacological agents. Thus, agents that inhibit PKC isozymes may block tumor progression. Information on the effects of aloe–emodin on cell proliferation and PKC isozymes is important because PKC overproduction has been linked with the rapid growth rate of gliomas [11], [12].
In this investigation, we evaluated aloe–emodin's antitumor effect on the cell cycle, cell proliferation, PKC activity, PKC isozyme content and apoptosis in transformed glia cell line (SVG) [13] and human glioma U-373MG cell line (U-373MG) which are a highly lethal brain tumor cell line.
Section snippets
Aloe–emodin
Aloe–emodin (1,8-dihydroy-3-[hydroxymethyl]-anthraquione) was purchased from Sigma (catalogue number A7687; St. Louis, MO).
Cell culture
The U-373MG and SVG transformed cell lines (glial cells transformed with the human papovavirus JCV; [13]) were obtained from the American Tissue Culture Collection (Rockville, MD). Cells were seeded (1×106) and grown as monolayers in 75-cm2 flasks containing 90% Dulbecco's modified Eagle's media (DMEM), 10% fetal calf serum (FCS), 2 mM l-glutamine, 4.5 gm/l glucose and
Aloe–emodin delays DNA synthesis (S) phase progression
To establish the cell cycle effects of aloe–emodin on SVG transformed glial cells and U-373MG glioma cells, we used confluent cultures to obtain cells with a high quiescence/Gap 1 (G0/G1) cell population and attempted a reversible G0/G1 arrest by serum starvation. Cells were grown to confluence and serum starved for 48 h. The cell cycle was initiated by serum addition in combination with either dimethylsulfoxide (DMSO; vehicle control) or aloe–emodin (40 μM; dissolved in DMSO). This
Discussion
Our experiments provide further support for aloe–emodin as a potential anticancer chemotherapeutic drug. The data presented here established that aloe–emodin delays S phase progression, inhibits SVG and U-373MG cell proliferation, decreases PKC activity, reduces PKC isozyme protein content (with the exception of PKC-ι) and induces apoptosis, as judged by a reduction in PARP, cleavage of caspase 7 and a decrease in survivin. Other laboratories have published the chemopreventive [30] and
Acknowledgements
We acknowledge the important contribution of the Flow Cytometry Core, H. Lee Moffitt Cancer Center. This project was supported in part by the Research Service of the Veterans' Administration and The Aloe Institute.
References (30)
- et al.
Effects and mechanisms of aloe–emodin on cell death in human lung squamous cell carcinoma
Eur. J. Pharmacol.
(2001) - et al.
Aloe–emodin inhibited N acetylation and DNA adduct of 2-aminofluorene and arylamine N-acetyltransferase gene expression in mouse leukemia L 1210 cells
Leuk. Res.
(2003) - et al.
Emodin induces apoptosis in human promyeloleukemic HL-60 cells accompanied by activation of caspase 3 cascade but independent of reactive oxygen species production
Biochem. Pharmacol.
(2002) - et al.
The antiproliferative activity of aloe–emodin is through p53 dependent and p21-dependent apoptotic pathway in human hepatoma cell lines
Life Sci.
(2002) - et al.
Molecular cloning and characterization of PKCiota, an atypical isoform of PKC derived from insulin-secreting cells
J. Biol. Chem.
(1993) A rapid and sensitive method for the quantitation of microgram quantities of protein utilizing the principle of protein–dye binding
Anal. Biochem.
(1976)- et al.
Atypical protein kinase C iota protects human leukemia cells against drug-induced apoptosis
J. Biol. Chem.
(1997) - et al.
Protein kinase C iota protects neural cells against apoptosis induced by amyloid beta-peptide
Mol. Brain Res.
(2000) - et al.
Chemopreventive effects of emodin and cassiamin B in mouse skin carcinogenesis
Cancer Lett.
(2002) - et al.
Aloe–emodin is a new type of anticancer agent with selective activity against neuroectodermal tumors
Cancer Res.
(2000)
Protein kinase C involvement in aloe–emodin and emodin-induced apoptosis in lung carcinoma cell
Br. J. Pharmacol.
Tumor inhibitors 114 aloe emodin: antileukemic principle isolated from Rhamus frangula L.
Lloydia
The effect of aloe emodin on the proliferation of a new Merkel carcinoma cell line
Am. J. Dermatopathol.
Intracellular signally by hydrolysis of phospholipids and activation of protein kinase C
Science
Inhibition of growth of established human glioma cell lines by modulators of the protein kinase-C system
J. Neurosurg.
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