|
||
Brief Definitive Reports |
by an ICE/CED 3-like Protease Induces Characteristics of Apoptosis






Division of Cancer Pharmacology, Dana-Farber Cancer Institute, Harvard Medical School, Boston, Massachusetts 02115
| Abstract |
|---|
|
|
|---|
is proteolytically activated at the onset of apoptosis induced by DNA-damaging agents, tumor necrosis factor, and anti-Fas antibody. However, the relationship of PKC
cleavage to induction of apoptosis is unknown. The present studies demonstrate that full-length PKC
is cleaved at DMQD330N to a catalytically active fragment by the cysteine protease CPP32. The results also demonstrate that overexpression of the catalytic kinase fragment in cells is associated with chromatin condensation, nuclear fragmentation, induction of sub-G1 phase DNA and lethality. By contrast, overexpression of full-length PKC
or a kinase inactive PKC
fragment had no detectable effect. The findings suggest that proteolytic activation of PKC
by a CPP32-like protease contributes to phenotypic changes associated with apoptosis.
The protein kinase C (PKC) family consists of multiple subspecies that possess a conserved catalytic domain. The classic or group A isoforms (
The nematode Ced-3 cysteine protease is related to the mammalian interleukin-1β converting enzyme (ICE) (5, 6). The demonstration that overexpression of Ced-3 or ICE induces apoptosis has provided support for involvement of these cysteine proteases in cell death pathways (7). ICE/ Ced-3 family members include Nedd2/Ich-1, CPP32/ YAMA/apopain, Tx/Ich-2/ICErelII, ICErelIII, Mch2, Mch3/ ICE-LAP3/CMH-1 (reviewed in reference 8), ICE-LAP6 (9), FLICE/Mch5 (10, 11), and Mch4 (11). ICE cleaves the precursor of IL-1β to the active cytokine (6, 12, 13). Other known substrates of the ICE/Ced-3 family include: (a) poly (ADP-ribose) polymerase (PARP) which is cleaved by CPP32, Mch3 and Ced-3, but not ICE (14–16); and (b) DNA-dependent protein kinase (DNA-PK), the U1 small nuclear ribonucleoprotein and D4-GDP dissociation inhibitor for the Rho family GTPases (D4-GDI), which are cleaved by CPP32 (17, 18). However, the functional role of these cleavage products in the induction of apoptosis is unclear.
The present results demonstrate that PKC
Analysis of Peptide Proteolysis.
Cell Transfections.
, β, and
) require Ca2+ for activity and contain cysteine-rich motifs that confer phospholipid-dependent binding of diacylglycerol (1). The group A PKCs are cleaved at the third variable region (V3) by the neutral proteases, calpains I and II, to catalytically active fragments (2). Recent studies have demonstrated that the Ca2+-independent
isoform, and not the group A PKCs, is selectively cleaved at V3 to a catalytically active fragment in cells induced to undergo apoptosis (3, 4). Inhibition of apoptosis by overexpression of Bcl-2 or Bcl-xL is associated with a block of PKC
cleavage (3, 4). The finding that PKC
is cleaved at a site (DMQD/N) adjacent to aspartic acid has supported the potential involvement of aspartate-specific cysteine proteases which are known to be activated during apoptosis.
is cleaved by CPP32 and not certain other ICE/Ced-3 family members. We also demonstrate that overexpression of the PKC
catalytic fragment is involved in the induction of phenotypic changes that are characteristic of apoptosis.
![]()
Materials and Methods
Top
Abstract
Materials and Methods
Results and Discussion
References
In Vitro Cleavage of PKC
and PARP.
The full-length PKC
cDNA was cloned into the SpeI and BamH1 sites of a modified pSVβ plasmid (Clontech, Palo Alto, CA). PKC
(D327A/D330A) was generated in two steps by overlapping primer extension. PARP cDNA was generated by PCR cloning. The proteins were labeled with [35S]methionine by coupled transcription and translation reactions (Promega, Madison, WI). Labeled proteins were incubated with 5 µg/ml Escherichia coli-derived CPP32β in 50 mM Hepes (pH 7.5), 10% glycerol, 2.5 mM DTT, and 0.25 mM EDTA at room temperature for 30 min. The reaction products were analyzed by electrophoresis in 10-20% SDS–polyacrylamide gels and then autoradiography. For the kinase assays, full-length PKC
, PKC
(D327A/D330A), PKC
catalytic fragment (CF), and PKC
CF(K-R) were prepared by coupled transcription and translation. PKC
and PKC
(D327A/D330A) were incubated with 5 µg/ml CPP32β at room temperature for 30 min. Protein kinase assays using MBP as a substrate were performed as described (PKC Assay Kit; GIBCO BRL, Gaithersburg, MD).
Peptides were synthesized and purified to
95% by standard methods and confirmed by mass spectrometry. Reaction mixtures (810 µl) contained: 100 mM Hepes (pH 7.5), 20% (vol/vol) glycerol, 5 µM dithiothreitol, 0.5 mM EDTA, and 380 ng N-His CPP32 (19). Peptide substrates were added to final concentrations of 10 µM. The reaction mixtures were incubated at 30°C. Aliquots were removed at 10 min intervals for 60 min and added to vials containing 3 M HCl to stop the reactions. The amount of substrate remaining at each time was quantitated by reverse phase HPLC. Data were fit to the equation (St/So) = e–kt, where k is the decay rate constant equal to Vmax/Km. Observed Vmax/Km values were normalized to 1.00 for the PARP peptide.
Cells were seeded at a density of 1.7 x 105 in each well of 6-well dishes 24 h before transfection. For each well, 2 µg DNA construct and 0.5 µg pSvβ plasmid containing β-gal were coprecipitated with calcium phosphate. Cells were incubated with the coprecipitate for 30 h at 37°C and then analyzed by X-gal staining. Cells (1.7 x 105/well) were also transfected with 2 µg DNA construct for 30 h at 37°C, fixed with 4% paraformaldehyde, postfixed with 5% acetic acid in ethanol and then stained with 5 µg/ml Hoechst dye. For sub-G1 DNA content, cells transfected by lipofectamine were stained with propidium iodide and monitored by FACScan®. Chromatin condensation was assessed by staining with acridine orange and ethidium bromide (20).
![]()
Results and Discussion
Top
Abstract
Materials and Methods
Results and Discussion
References
To determine whether PKC
is cleaved by one of the known ICE-like proteases, full-length 78-kD PKC
labeled with [35S]methionine was incubated with purified recombinant proteases. Cleavage of PKC
to a 40-kD fragment was observed with purified CPP32β (14) (Fig. 1 A). In contrast, ICE failed to cleave PKC
at concentrations up to 600 U/µl (3). The related Ich-1, Ich-2, Mch2, Mch3, and ICErelIII proteases also failed to cleave PKC
(data not shown). Because PKC
is cleaved at DMQD330N in vivo (3, 4), we asked whether this site is responsible for CPP32mediated cleavage in vitro. CPP32 may prefer peptidic substrates with aspartic acid at the P1 and P4 positions (15). Consequently, we prepared a PKC
mutant with substitution of D327A and D330A. Incubation with CPP32 resulted in no detectable CPP32-mediated cleavage of this mutant to the 40-kD catalytic fragment, while there was partial digestion to a species of
55 kD (not observed with wild-type substrate) (Fig. 1 A). Recombinant CPP32 also cleaved the 116-kD full-length PARP to the predicted 85-kD fragment (14, 15) (Fig. 1 A). Using peptides derived from the cleavage sites of PARP and PKC
in proteolytic assays, we found that CPP32 cleaves both substrates and not a peptide spanning the IL-1β maturation site (Table 1). These findings confirm that PKC
, like PARP, is a substrate for CPP32.
|
|
by CPP32 is associated with activation of the kinase function. Fulllength PKC
exhibited a low level of myelin basic protein (MBP) phosphorylation, while incubation with CPP32 resulted in a greater than sixfold increase in kinase activity (Fig. 1 B). In contrast, CPP32 had no detectable effect on kinase function of the PKC
(D327A/D330A) mutant (Fig. 1 B). A recombinant 40-kD CF of PKC
(amino acids 331676) exhibited constitutive kinase activity, while a mutant of the fragment with K-378 in the ATP binding site mutated to R (K378R; designated K-R) yielded background levels of MBP phosphorylation found with control bacterial lysates (Figs. 1, A and B). These findings collectively demonstrate that CPP32-mediated cleavage of the DMQD330N site activates PKC
.
To study the role of PKC
in apoptosis, we used the transient HeLa cell transfection system previously found to demonstrate induction of apoptosis by ICE-like proteases (7). Cotransfection of the kinase inactive PKC
CF(K-R) mutant with the β-galactosidase (β-gal) marker gene had little effect on HeLa cell morphology (Fig. 2 A). Most of the blue X-gal positive cells remained flat and attached to the dish (Fig. 2 A). Cotransfection of the kinase active PKC
CF and β-gal resulted in condensed, small blue cells (Fig. 2 B), consistent with the induction of apoptosis (7). Similar findings were obtained with NIH3T3 cells (Figs. 2, C and D). Overexpression of PKC
in both cell types also resulted in detachment of non-viable cells into the culture medium.
|
had no detectable changes in nuclear morphology (Fig. 3 A), but overexpression of PKC
CF resulted in fragmented nuclei (Fig. 3 B). Transfection of kinase inactive PKC
CF(K-R) was associated with a normal nuclear morphology (Fig. 3 C). The changes observed with expression of the PKC
CF were also compared to those found upon exposure to 1-β-D-arabinofuranosylcytosine (ara-C), a DNA-damaging agent that induces proteolytic cleavage of PKC
and apoptosis (4). Treatment of HeLa cells with ara-C resulted in a similar pattern of nuclear fragmentation (Fig. 3 D).
|
CF are associated with induction of apoptosis, we assessed the effects of transfection on the appearance of HeLa cells with sub-G1 DNA content. Transfection of the empty vector, full-length PKC
or PKC
CF(K-R) resulted in 10-15% of cells with sub-G1 DNA (Fig. 4 A and data not shown). By contrast, transfection of PKC
CF was associated with 30– 35% of cells with sub-G1 DNA (Fig. 4 A). Cells were also stained with acridine orange and ethidium bromide to assess chromatin condensation (20). Transfection of PKC
CF, but not PKC
CF(K-R), resulted in the appearance of bright yellow-green nuclear staining of condensed chromatin (Fig. 4 B).
|
CF expression on cell viability, we cotransfected PKC
CF or PKC
CF(K-R) and the green fluorescence gene (Clontech) into HeLa cells. Positive transfectants were selected by flow cytometry, reseeded in culture medium and assayed at 24 h for viability by trypan blue exclusion. Less than 5% of the PKC
CF transfectants were viable, while over 90% of the kinase inactive PKC
CF(K-R) transfectants were viable and attached to the dish. Viability of 90–95% was observed after transfection of the null vector and sorting. We conclude that the kinase active catalytic domain of PKC
induces characteristics typical of cells undergoing apoptosis: (a) size reduction and round morphology; (b) nuclear fragmentation; (c) chromatin condensation; (d) sub-G1 DNA content; and (e) detachment and loss of viability.
Multiple events that lead to destruction of nuclear and cytoplasmic integrity are probably required for apoptosis. Activation of ICE-family proteases may be a central trigger, resulting in the cleavage of substrates such as PARP (21), lamin B1 (22, 23), topoisomerase 1 (23), D4-GDI (18), DNA-PK, and the U1 small nuclear ribonucleoprotein (17). PKC
, but not PKC
, β,
, or
, is also cleaved at the onset of apoptosis (3, 4). Little is known about the physiological function of PKC
(24, 25). We demonstrate that PKC
is cleaved by CPP32 and not other ICE/Ced-3 family members in vitro. The results also demonstrate that expression of the PKC
catalytic fragment induces morphologic changes characteristic of apoptosis. We propose that the proteolytic cleavage of PKC
is a key mediator of nuclear fragmentation and cell death, and not a bystander effect of protease activation. Moreover, the finding that proteolytic activation of PKC
is blocked by Bcl-2 and Bcl-xL suggests that these anti-apoptotic proteins act upstream to this event (3). Elucidation of the substrates phosphorylated as a consequence of PKC
cleavage should provide insights into the pathways activated by the catalytic fragment.
Submitted: 13 August 1996
| References |
|---|
|
|
|---|
1 Nishizuka Y. Intracellular signaling by hydrolysis of phospholipids and activation of protein kinase C, Science (Wash DC), 1992, 258, 607–614.
2 Kishimoto, A. 1990. Limited proteolysis of protein kinase C by calpain, its possible implication. In The Biology and Medicine of Signal Transduction. Y. Nishizuka, M. Endo, and C. Tanaka, editors. Raven Press, New York. 472–477.
3 Emoto Y, Manome G, Meinhardt G, Kisaki H, Kharbanda S, Robertson M, Ghayur T, Wong WW, Kamen R, Weichselbaum R & Kufe D. Proteolytic activation of protein kinase C
by an ICE-like protease in apoptotic cells, EMBO (Eur Mol Biol Organ) J, 1995, 14, 6148–6156.[Medline]
4 Emoto Y, Kisaki H, Manome Y, Kharbanda S & Kufe D. Activation of protein kinase C
in human myeloid leukemia cells treated with 1-β-D-arabinofuranosylcytosine, Blood, 1996, 87, 1990–1996.
5 Hugunin M, Quintal LJ, Mankovich JA & Ghayur T. Protease activity of in vitro transcribed and translated Caenorhabditis elegans cell death gene (ced-3) product, J Biol Chem, 1996, 271, 3517–3522.
6 Yuan J, Shaham S, Ledoux S, Ellis HM & Horvitz HR. The C. eleganscell death gene ced-3 encodes a protein similar to mammalian interleukin-1β-converting enzyme, Cell, 1993, 75, 641–752.[Medline]
7 Miura M, Zhu H, Rotello R, Hartweig EA & Yuan J. Induction of apoptosis in fibroblasts by IL-1β-converting enzyme, a mammalian homolog of the C. eleganscell death gene ced-3, Cell, 1993, 75, 653–660.[Medline]
8 Nicholson DW. ICE/CED3-like proteases as therapeutic targets for the control of inappropriate apoptosis, Nat Biotechnol, 1996, 14, 297–301.[Medline]
9 Duan H, Orth K, Chinnaiyan AM, Poirier GG, Froelich CJ, He W-W & Dixit VM. ICE-LAP6, a novel member of the ICE/Ced-3 gene family, is activated by the cytotoxic T cell protease granzyme B, J Biol Chem, 1996, 271, 16720–16724.
10 Muzio M, Chinnaiyan AM, Kischkel FC, O'Rourke K, Shevchenko A, Ni J, Scaffidi C, Bretz JD, Zhang M, Gentz R et al.. FLICE, a novel FADD-homologous ICE/ CED-3-like protease, is recruited to the CD95 (Fas/APO-1) death-inducing signaling complex, Cell, 1996, 85, 817–827.[Medline]
11 Fernandes-Alnemri T, Armstrong RC, Krebs J, Srinivasula SM, Wang L, Bullrich F, Fritz L, Trapani JA, Tomaselli KJ, Litwack G & Alnemri ES. In vitro activation of CPP32 and Mch3 by Mch4, a novel human apoptotic cysteine protease containing two FADD-like domains, Proc Natl Acad Sci USA, 1996, 93, 7464–7469.
12 Cerretti DP, Kozlosky CJ, Mosley B, Nelson N, Ness KV, Greenstreet TA, March CJ, Kronheim SR, Druck T, Canizzaro LA et al.. Molecular cloning of the interleukin-1β-converting enzyme, Science (Wash DC), 1992, 256, 97–100.
13 Thornberry NA, Bull HG, Calaycay JR, Chapman KT, Howard AD, Kostura MJ, Miller DK, Molineaux SM, Weidner JR, Aunins J et al.. A novel heterodimeric cysteine protease is required for interleukin-1β processing in monocytes, Nature (Lond), 1992, 356, 768–774.[Medline]
14 Tewari M, Quan LT, O'Rourke K, Desnoyers S, Zeng Z, Beidler DR, Poirier GG, Salvesen GS & Dixit VM. Yama/CPP32β, a mammalian homolog of CED-3, is a CrmA-inhibitable protease that cleaves the death substrate poly(ADP-ribose) polymerase, Cell, 1995, 81, 801–809.[Medline]
15 Nicholson DW, Ali A, Thornberry NA, Vaillancourt JP, Ding CK, Gallant M, Gareau Y, Griffin PR, Labelle M, Lazebnik YA et al.. Identification and apoptosis, Nature (Lond), 1995, 376, 37–43.[Medline]
16 Fernandes-Alnemri T, Takahashi A, Armstrong R, Krebs J, Fritz L, Tomaselli KJ, Wang L, Yu Z, Croce CM, Salveson G, Earnshaw WC, Litwack G & Alnemri ES. Mch3, a novel human apoptotic cysteine protease highly related to CPP32, Cancer Res, 1995, 55, 6045–6052.
17 Casciola-Rosen L, Nicholson DW, Chong T, Rowan KR, Thornberry NA, Miller DK & Rosen A. Apopain/CPP32 cleaves proteins that are essential for cellular repair: a fundamental principle of apoptotic death, J Exp Med, 1996, 183, 1957–1964.
18 Na S, Chuang T-H, Cunningham A, Turi TG, Hanke JH, Bokoch GM & Danley DE. D4-GDI, a substrate of CPP32, is proteolyzed during Fas-induced apoptosis, J Biol Chem, 1996, 271, 11209–11213.
19 Bump NJ, Hackett M, Hugunin M, Seshagiri S, Brady K, Chen P, Ferenz C, Franklin S, Ghayur T, Li P et al.. Inhibition of ICE family proteases by baculovirus antiapoptotic protein p35, Science (Wash DC), 1995, 269, 18851888.
20 McGahon AJ, Martin SJ, Bissonnette RP, Mahboubi A, Shi Y, Mogli RJ, Nishioka WK & Green DR. The end of the (cell) line: methods for the study of apoptosis in vitro, Methods Cell Biol, 1995, 46, 153–185.[Medline]
21 Kaufmann SH, Desnoyers S, Ottaviano Y, Davidson NE & Poirier GG. Specific proteolytic cleavage of poly(ADP-ribose) polymerase: an early marker of chemotherapy-induced apoptosis, Cancer Res, 1993, 53, 3976–3985.
22 Neamati N, Fernandez A, Wright S, Kiefer J & McConkey DJ. Degradation of lamin B1 precedes oligonucleosomal DNA fragmentation in apoptotic thymocytes and isolated thymocyte nuclei, J Immunol, 1995, 154, 3788–3795.[Abstract]
23 Voelkel-Johnson C, Entingh AJ, Wold WSM, Gooding LR & Laster SM. Activation of intracellular proteases is an early event in TNF-induced apoptosis, J Immunol, 1995, 154, 1707–1716.[Abstract]
24 Watanabe T, Ono Y, Taniyama Y, Hazama K, Igarashi K, Ogita K, Kikkawa U & Nishizuka Y. Cell division arrest induced by phorbol ester in CHO cells overexpressing protein kinase C-
subspecies, Proc Natl Acad Sci USA, 1992, 89, 10159–10163.
25 Mischak H, Goodnight J, Kolch W, Martiny-Baron G, Schaechtle C, Kazanietz MG, Blumberg PM, Pierce JH & Mushinski JF. Overexpression of protein kinase c-
and -
in NIH 3T3 cells induces opposite effects on growth, morphology, anchorage dependence, and tumorigenicity, J Biol Chem, 1993, 268, 6090–6096.
This article has been cited by other articles:
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| TABLE OF CONTENTS |
|