Up-regulated P21CIP1 expression is part of the regulation quantitatively controlling serum deprivation-induced apoptosis

Mild Hyperthermia-Induced Myogenic Differentiation in Skeletal Muscle Cells: Implications for Local Hyperthermic Therapy for Skeletal Muscle Injury

The percutaneous application of controlled temperature on damaged muscle is regarded as a prevalent remedy. However, specific mechanisms are not completely understood. Therefore, cellular behaviors of myoblasts were investigated under a physiological hyperthermic temperature. The myoblasts were cultured under no treatment (NT, 37°C, 24 h/day), intermittent heat treatment (IHT, 39°C, 2 h/day), and continuous heat treatment (CHT, 39°C, 24 h/day) during proliferation, migration, or myogenic differentiation. Although the effects of mild heat on migration were not observed, the proliferation was promoted by both IHT and CHT. The myogenic differentiation was also enhanced in a treatment time-dependent manner, as evidenced by an increase in myotube size and fusion index. The gene expressions of mitochondrial biogenesis (Pgc-1α, Nrf1, and Tfam), a subset of mitochondrial dynamics (Mfn1 and Drp1), and a myogenic regulatory factor (myogenin) were increased in a heat treatment time-dependent manner. Interestingly, the mild heat-induced myogenic differentiation and myogenin expression were retarded significantly in PGC-1α-targeted siRNA-transfected cells, suggesting that mild hyperthermia promotes myogenic differentiation via the modulation of PGC-1α. This study provides cellular evidence supporting that local hyperthermic treatment at 39°C is regarded as an effective therapeutic strategy to promote satellite cell activities in regenerating myofibers.

GDF11/BMP11 activates both smad1/5/8 and smad2/3 signals but shows no significant effect on proliferation and migration of human umbilical vein endothelial cells

GDF11/BMP11, a member of TGF-β superfamily, was reported to rejuvenate heart, skeletal muscle and blood vessel architecture in aged mice. However, the rejuvenative effects of GDF11 were questioned recently. Here, we investigated the effects of GDF11 on smad and non-smad signals in human umbilical vein endothelial cells (HUVECs) and the effects of GDF11 on proliferation and migration of HUVECs and primary rat aortic endothelial cells (RAECs). GDF11 factor purchased from two different companies (PeproTech and R&D Systems) was comparatively studied. Western blot was used to detect the protein expressions. The cell viability and migration were examined by using MTT and wound healing assays. Results showed that GDF11 activated both smad1/5/8 and smad2/3 signals in HUVECs. GDF11 increased protein expression of NADPH oxidase 4(NOX4) in HUVECs. GDF11 showed no significant effect on the protein level of p38, p-p38, ERK, p-ERK, Akt, p-Akt (Ser473) and p-Akt(Thr308), but increased the protein level of p-JNK and p-AMPK in HUVECs, and these increases were inhibited by antioxidant mitoTEMPO treatment. GDF11 slightly increased cell viability after short-term treatment and slightly decreased cell viability after long-term treatment. GDF11 showed no significant effect on cell proliferation and migration. These data indicated that the notion of GDF11 as a rejuvenation-related factor for endothelial cells needs to be cautious.

Short-term serum deprivation confers sensitivity to taxanes in platinum-resistant human ovarian cancer cells

BACKGROUND

Based on the evidences showing that serum deprivation provokes apoptosis in a variety of cells, we have investigated the effect of serum deprivation on drug sensitivity.

METHODS

After human ovarian cancer cells were preincubated in 0.5 % serum containing medium for 12 hours, cellular drug sensitivities were determined by colony-forming assay.

RESULTS

Serum deprivation treatment resulted in significant increase in paclitaxel sensitivity by factors of mean ± SD, 148.6 ± 28.1 and 10.1 ± 1.0 (n = 3; P < 0.001) fold in platinum-resistant C13 and CP70 cells, respectively. Similarly, serum deprivation induced significant docetaxel sensitivity in these cell lines. However, no enhancement effect of serum deprivation was observed in platinum-sensitive 2008 and A2780 cells. Serum deprivation did not have any effect on the sensitivities to cisplatin, vincristin, and doxorubicin in all of these cells. More than 7-fold increase of apoptotic cells were observed in C13 or CP70 cells when they were treated by serum deprivation followed by paclitaxel compared with the treatment of either serum deprivation or paclitaxel alone. Confocal laser microscopy using rhodamine 123 and flow cytometric analysis with 3,3'-dihexyloxacarbocyanine iodide revealed that serum deprivation decreased mitochondrial membrane potential in C13 or CP70 cells, whereas no change was observed in 2008 and A2780 cells. This indicates that serum deprivation induced depolarization specifically in platinum-resistant cells. Electron microscopy revealed that serum deprivation caused regeneration of mitochondrial matrix structure in C13 or CP70 cells where mitochondria were usually destructed and disappeared.

DISCUSSIONS

These results indicate that serum deprivation confers taxane hypersensitivity specifically in platinum-resistant cells by recovering their impaired mitochondrial functions. The evidence might be clinically beneficial for the development of new chemotherapeutic technology, particularly for the patients with platinum-resistant ovarian cancer.

20-Hydroxyeicosatetraenoic acid inhibits the apoptotic responses in pulmonary artery smooth muscle cells

20-Hydroxyeicosatetraenoic acid (20-HETE), a omega-hydroxylation product of arachidonic acid catalyzed by cytochrome P450 4A (CYP4A), plays a role in vascular smooth muscle remodeling. Although its effects on angiogenic responses are known, it remains unclear whether 20-HETE acts on apoptosis of pulmonary arterial smooth muscle cells (PASMC), an important step in PASMC remodeling, and what pathways are involved in the process. Here we show evidence for the missing information. The effect of 20-HETE on PASMC apoptosis and the apoptosis-associated signaling pathways were determined with cell viability assay, Annexin V and propidium idodide binding, terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL), mitochondrial potentials assay, caspase activity assay and Western blots. We found that exogenous 20-HETE suppressed the serum deprivation-induced loss of bovine PASMCs and prevented Annexin V binding, DNA nick end labeling and chromatin condensation. The effect was worsened by 17-octadecynoic acid (17-ODYA), which inhibited the production of endogenous 20-HETE. Furthermore, 20-HETE induced the expression of bcl-2, maintained the stability of mitochondria membrane, and relieved the activation of caspase-9 and caspase-3. Such effects were reversed in the presence of 17-ODYA. Thus, these findings indicate that 20-HETE protects PASMCs against apoptosis by acting on, at least in part, the intrinsic apoptotic pathway.

c-Jun NH2-terminal kinase decreases ubiquitination and promotes stabilization of p21(WAF1/CIP1) in K562 cell

Proteasome-dependent degradation of regulatory proteins is a known mechanism of cell cycle control. p21(WAF1/CIP1) (p21), a negative regulator of the cell division cycle, exhibits proteasome-sensitive turnover and ubiquitination. In the present study, we analyzed the regulatory effects of JNK1 on p21 protein accumulation in p53 null K562 cells. We found that JNK1 (wild type, WT) mediated H(2)O(2)-induced p21 protein up-regulation. Over-expression of JNK1 (WT) could elevate endogenous p21 protein level but did not affect p21 mRNA level and also prolong the p21 half-life as well as inhibited the p21 ubiquitination. These findings indicated that JNK1 could regulate cellular p21 level via inhibiting ubiquitination of p21, which provided a new insight for analyzing the regulatory effect of JNK after stress.

p21 (Waf1/Cip1) and FasL gene activation via Sp1 and NFkappaB is required for leukemia cell survival but not for cell death induced by diverse stimuli

The molecular mechanisms of the cellular response to different apoptotic effectors are only partially understood. Herein, the role of transcription factors, Sp1 and NFkappaB in differentiation-related and etoposide-induced apoptosis was examined in a number of human leukemia cell lines (HL-60, NB4, HEL, THP-1, K562). This was investigated with respect to the recruitment of one cell-cycle regulating gene, p21 and one cell death gene, FasL. Using electrophoretic mobility shift assay (EMSA), we consistently observed Sp1 and NFkappaB binding activity to the promoter of either gene during cell differentiation and the decrease associated with apoptosis upon long-term treatment with differentiation inducers in HL-60, NB4 and HEL cells. By contrast, Sp1 and NFkappaB binding capacities were lost in all myeloid cell lines undergoing etoposide-induced fast apoptosis. This effect was eliminated by the broad-spectrum caspase inhibitor, benzyloxycarbonyl-valinyl-alaninyl-aspartyl fluoromethylketone, thus restoring transcription factors' binding activity. However, sustained NFkappaB binding to the FasL promoter was noticed in apoptosis undergoing HEL cells treated by etoposide. Our results suggest that p21 and FasL gene activation is required for myeloid leukemia cell survival or maturation but not for cell death via Sp1 and NFkappaB as regulators of these genes. The findings also support the idea of a common mechanism for cellular responses to different apoptotic effectors in malignant hematopoietic cell lines.

p53 mediates a default programme of mammary gland involution in the absence of STAT3

Previous studies have demonstrated a proapoptotic role for the transcription factor STAT3 in involuting murine mammary epithelium, resulting in delayed involution and lower levels of apoptosis in the STAT3 null gland relative to wild-type controls. As p53 was implicated in the eventual involution of the STAT3 null gland, we examined the effect of STAT3 loss in the mammary gland in a p53 null background. Combined loss of STAT3 and p53 severely perturbed involution, with hyperdelayed loss of epithelium and reappearance of adipocytes. The early apoptotic response was almost completely abrogated, although elevated levels of delayed apoptosis persisted at days 6, 17 and 4 weeks of involution in STAT3-p53 doubly null mammary glands. A 5.7-fold upregulation of the cyclin-dependent kinase inhibitor p21Waf1 at 3 days of involution in STAT3 null glands was abolished in STAT3-p53 doubly null glands -- suggesting that the critical factor triggering delayed involution in the STAT3 null gland is a p53-dependent rise in p21Waf1 levels around day 3 of involution. Further, STAT3-p53 doubly null glands showed significantly higher levels of proliferation compared to STAT3 or p53 singly null (or wild-type) glands at days 6, 17 and 4 weeks of involution. Combined loss of STAT3 and p53 therefore results in hyperdelayed involution, demonstrating their synergistic physiological roles in normal involution. This inappropriate retention of p53-deficient cells may represent a novel mechanism of tumour predisposition.

Down-regulation of p21WAF1 promotes apoptosis in senescent human fibroblasts: involvement of retinoblastoma protein phosphorylation and delay of cellular aging

It has been suggested that genes which exercise checkpoint control during cell cycle traverse are equally important to the process of apoptotic cell death. In this study, we show that the key cell cycle regulatory gene p21(WAF1) is also involved in the execution of apoptosis. p21(WAF1) expression was down-regulated during NaBu-induced apoptosis of senescent normal diploid human 2BS fibroblasts. Conversely, when p21(WAF1) expression was actively suppressed in 2BS cells by a stably transfected antisense p21(WAF1) construct, apoptosis was accelerated and senescence was delayed, as shown by several markers of cell aging. Down-regulation of p21(WAF1) by antisense caused an increase in the phosphorylation and inactivation of pRb. Phosphorylation of pRb was further enhanced upon induction of apoptosis by NaBu. Our results suggest that p21(WAF1), acting through the phosphorylation of pRb, regulates whether 2BS cells cease to proliferate and become senescent but resistant to apoptosis, or whether they accelerate proliferation while becoming more susceptible to apoptotic stimuli.

Sp1 is involved in the transcriptional activation of p16(INK4) by p21(Waf1) in HeLa cells

Both p16(INK4) and p21(Waf1) are very important negative regulators of the cell cycle. In this study we examined the effects of p21(Waf1) on the transcription of p16(INK4). We determined that p21(Waf1) can activate the transcription of p16(INK4), and that this effect is GC-box dependent. We also found that the transcription factor Sp1 plays a key role in this event. Upregulation of Sp1 contributes to the transcriptional activation and protein level of p16(INK4) mediated by p21(Waf1), and is a potential point of cooperation between the p16/pRb and p14 (ARF)/p53 tumor suppressor pathways.

Endogenous p21WAF1/CIP1 status predicts the response of human tumor cells to wild-type p53 and p21WAF1/CIP1 overexpression

Expression of exogenous wild-type (wt) p53 protein can suppress the growth and/or induce apoptosis in different tumor cells. The effect of exogenous p21(WAF1/CIP1) expression is more controversial: while it can induce apoptosis in some cells, it can protect against p53-mediated apoptosis in others. We used adenoviral vectors to introduce p53 and p21(WAF1/CIP1) genes into human tumor cell lines with different p53 and/or p21(WAF1/CIP1) status. The cell growth inhibition and the induction of apoptosis were measured. Overexpression of wt p53 induced more efficient growth inhibition and apoptosis in SW 620 (mutant p53) and HeLa (inactivated p53 protein) than in MCF-7 (wt p53) and CaCo-2 cell line, which was the most resistant to p53 overexpression despite the p53 mutation. Unlike HeLa and SW 620 cells, the basal p21 protein level was readily detected in CaCo-2 and MCF-7 cells. Overexpression of p21(WAF1/CIP1) gene induced somewhat less pronounced growth inhibition of all cell lines tested, but it also induced apoptosis in HeLa and SW 620 cells. These results suggest that the basal, but not the inducible, levels of p21(WAF1/CIP1) protein in tumor cells could protect from p53-mediated apoptosis. On the other hand, overexpression of p21(WAF1/CIP1) gene itself can induce apoptosis in cells with no basal p21(WAF1/CIP1) protein level. Possible mechanisms of the differential response to these genes are discussed.

Tissue-specific p53 responses to ionizing radiation and their genetic modification: the key to tissue-specific tumour susceptibility?

Although little is understood of the underlying mechanisms, there are tissue-specific responses to tumourigenic and therapeutic agents and these responses are influenced by genetic factors. Ionizing radiation is an important tumourigenic and therapeutic agent for which there is substantial evidence for such tissue-dependent and genotype-dependent responses. Because the p53 tumour suppressor protein is a major determinant of cellular responses to radiation, the present study has investigated whether modification of the p53 pathway contributes to tissue-dependent and genotype-dependent responses using inbred strains of mice. Comparison of responses in haemopoietic and epithelial cells in irradiated C57BL/6 and DBA/2 mice revealed significant differences in p53 and apoptotic responses in different cell types and in different cells of the same type, reflecting the complexity of damage responses operating in the whole organism. The data suggest that p53-mediated up-regulation of Bax is a major determinant of apoptosis in the spleen, but not in the intestine, whereas p53-mediated induction of p21(waf1) plays an anti-apoptotic role in the spleen, but not in the intestine. It is also shown that p53 stabilization and differential transactivational activities towards Bax or p21(waf1) are influenced by genetic factors that act in a tissue-specific manner. Analysis of ATM, a potential mediator of differential p53 activation, indicates that this key regulator of radiation responses is preferentially induced in epithelial cells, but is unlikely to account for genetic modification of p53 or apoptotic responses in the mouse strains studied. Polymorphisms in the p53 or DNA-PKcs genes are also unlikely to account for the genetic modifications that are reported here. There are numerous further potential modifiers of the p53 pathway, but analysis of backcross and inter-cross mice demonstrates that genes responsible for the complex modification of these in vivo responses can be identified by linkage analysis. This approach has the potential to reveal new or unexpected interactions involving the p53 pathway that determine both short-term and long-term effects of radiation exposure and the basis of tissue-specific responses and tumour susceptibility.

Inhibition of ultraviolet B (UVB) induced apoptosis in A431 cells by mimosine is not dependent on cell cycle arrest

Ultraviolet (UV) radiation is a strong apoptotic trigger in many cell types. We have previously reported that a plant amino acid, mimosine (beta [N-(3-hydroxy-4-pyridone)]-alpha-aminopropionic acid), with a well-known reversible G1 cell cycle arrest activity can inhibit apoptosis induced by UV irradiation and RNA polymerase II blockage in human A431 cells. Here, apoptosis was measured with a fluorimetric caspase activation assay. Interestingly, the protective state was effective up to 24 h following removal of mimosine from the culture medium while cells were progressing in the cell cycle. Our results demonstrate that the protective effect of mimosine against UV-induced apoptosis can be dissociated from its G1 cell-cycle arrest activity.

Peptide elongation factor eEF1A-2/S1 expression in cultured differentiated myotubes and its protective effect against caspase-3-mediated apoptosis

Peptide elongation factor eEF1A-2/S1, which shares 92% homology with eEF1A-1/EF-1alpha, is exclusively expressed in brain, heart, and skeletal muscle. In these tissues, eEF1A-2/S1 is the only type 1A elongation factor expressed in adulthood because a transition from eEF1A-1/EF-1alpha to eEF1A-2/S1 occurs in early postnatal development. In this article, we report that the expression of eEF1A-2/S1 protein is activated upon myogenic differentiation. Furthermore, we show that upon serum deprivation-induced apoptosis, eEF1A-2/S1 protein disappears and is replaced by its homolog eEF1A-1/EF-1alpha in dying myotubes; cell death is characterized by the activation of caspase-3. In addition, we show that the continuous expression of eEF1A-2/S1 resulting from adenoviral gene transfer protects differentiated myotubes from apoptosis by delaying their death, thus suggesting a prosurvival function for eEF1A-2/S1 in skeletal muscle. In contrast, myotube death is accelerated by the introduction of the homologous gene, eEF1A-1/EF-1alpha, whereas cells transfected with antisense eEF1A-1/EF-1alpha are protected from apoptosis. These results demonstrate that the two sister genes, eEF1A-1/EF-1alpha and eEF1A-2/S1, regulate myotube survival with the former exerting prodeath activity and the latter a prosurvival effect.

v-Abl protein-tyrosine kinase up-regulates p21WAF-1 in cell cycle arrested and proliferating myeloid cells

v-Abl protein-tyrosine kinase (PTK) promotes cell survival without cell proliferation in interleukin (IL)-3-deprived IC.DP premast cells (1). We now show that in these conditions v-Abl PTK transcriptionally up-regulated the cyclin-dependent kinase inhibitor (CDKI) p21(WAF-1) and inhibited CDK2 and CDK4. When readdition of IL-3 stimulated cell proliferation, p21(WAF-1) was inactivated as a CDKI despite maintenance of elevated protein level. p21(WAF-1) was also up-regulated yet was nonfunctional as a CDKI when v-Abl PTK was activated in cells maintained in IL-3, but this occurred without increased p21(WAF-1) transcription. Using a C-terminal epitope-specific p21(WAF-1) antibody, v-Abl PTK-mediated increase in p21(WAF-1) could be detected in intact cells only in the presence of IL-3. This indicated different binding partners of p21(WAF-1) and/or protein conformation in nondividing or proliferating cells, respectively. The binding of CDK2, CDK4, or proliferating cell nuclear antigen to p21(WAF-1) and its subcellular localization were unchanged in the presence or absence of IL-3. However, two-dimensional analysis revealed different forms of up-regulated p21(WAF-1) in IL-3-deprived, nondividing cells compared with IL-3-stimulated proliferating cells. These data demonstrate that elevation of the CDKI p21(WAF-1) is not always sufficient for cell cycle arrest and indicate an IL-3-sensitive pathway for the inactivation of p21(WAF-1) function as a CDKI.

Different effects of genistein on molecular markers related to apoptosis in two phenotypically dissimilar breast cancer cell lines

The association between consumption of genistein-containing soybean products and lower risk of breast cancer suggests a cancer chemopreventive role for genistein. Consistent with this suggestion, exposing cultured human breast cancer cells to genistein inhibits cell proliferation, although this is not completely understood. To better understand how genistein works, the ability of genistein to induce apoptosis was compared in phenotypically dissimilar MCF-7 and MDA-MB-231 human breast cancer cells that express the wild-type and mutant p53 gene, respectively. After 6 days of incubation with 50 microM genistein, MCF-7 but not MDA-MB-231 cells, showed morphological signs of apoptosis. Marginal proteolytic cleavage of poly-(ADP-ribose)-polymerase and significant DNA fragmentation were also detected in MCF-7 cells. In elucidating these findings, it was determined that after 2 days of incubation with genistein, MCF-7 but not MDA-MB-231 cells, had significantly higher levels of p53. Accordingly, the expression of certain proteins modulated by p53 was studied next. Levels of p21 increased in both of the genistein-treated cell lines, suggesting that p21 gene expression was activated but in a p53-independent manner, whereas no significant changes in levels of the pro-apoptotic protein, Bax, were found. In MCF-7 cells, levels of the anti-apoptotic protein, Bcl-2, decreased slightly at 18-24 h but then increased considerably after 48 h. Hence, the Bax:Bcl-2 ratio initially increased but later decreased. These data suggest that at the genistein concentration tested, MCF-7 cells in contrast to MDA-MB-231 cells were sensitive to the induction of apoptosis by genistein, but Bax and Bcl-2 did not play clear roles.

Different impact of p53 and p21 on the radiation response of mouse tissues

Mammalian tissues differ dramatically in their sensitivity to genotoxic stress, although the mechanisms determining these differences remain largely unknown. To analyse the role of p53 and p21 in determination of tissue specificity to DNA damage in vivo, we compared the effects of gamma radiation on DNA synthesis on whole-body sections of wild type, p53-deficient and p21-deficient mice. A dramatic reduction in 14C-thymidine incorporation after gamma irradiation was observed in the majority of rapidly proliferating tissues of wild type and p21-/- but not in p53-/- mice, confirming the key role of p53 in determination of tissue response to genotoxic stress in vivo and suggesting that p53-mediated inhibition of DNA synthesis does not depend on p21. Rapid radiation induced p53-dependent apoptosis was mapped to the areas of high levels of p53 mRNA in radiation sensitive tissues analysed (white pulp in the spleen and bases of crypts in small intestine), indicating that p53 regulation at the mRNA level is a determinant of cellular sensitivity to genotoxic stress. High p53 mRNA expression is inherited as a recessive trait in cell-cell hybrids suggesting the involvement of a negative control mechanism in the regulation of p53 gene expression.

CD95/Fas signaling in T lymphocytes induces the cell cycle control protein p21cip-1/WAF-1, which promotes apoptosis

Ligation of CD95 on T lymphocytes resulted in the up-regulation of a cell cycle control protein, p21cip-1/WAF-1, an inhibitor of cyclin-dependent kinases. This up-regulation was completely blocked by the cysteine protease inhibitor Z-VAD-fmk (benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone), whereas DEVD-CHO (succinyl-Asp-Glu-Val-Asp-aldehyde), a caspase 3 inhibitor, had no effect. In Faslpr-cg mice, a point mutation in the death domain of CD95 results in failure to recruit FADD (Fas-associated death domain), and in the present study this mutation prevented both CD95-mediated apoptosis and p21cip-1/WAF-1 induction. During apoptotic cell death due to irradiation, p21cip-1/WAF-1 is up-regulated by a p53-dependent pathway that responds to DNA damage. However, CD95-induced up-regulation of p21cip-1/WAF-1 in T cells was p53-independent. T cells deficient in p21cip-1/WAF-1 were less susceptible to CD95-induced apoptosis. We conclude that in T cells, ligation of CD95 and activation of caspases cause the induction of p21cip-1/WAF-1, which acts to promote cell death.

Transcriptional repression of p21((Waf1/Cip1/Sdi1)) gene by c-jun through Sp1 site

Previously, we found that c-jun represses the tumor suppressor p21((Waf1/Cip1/Sdi1)) (p21) gene expression. In this study, we further investigated the mechanism of the inhibitory effect of c-jun on p21. After analysis of a series of deletion and point mutants of p21 promoter, we found that Sp1-3 site (-77 and -83) relative to the transcription start site played an important role for c-jun-repressing-responsive element in the p21 promoter. Both Sp1 and Sp3 transcription factors were the key factors for this event. However, the data from electrophoretic mobility shift assay indicated that c-jun did not change the Sp1 DNA-binding affinity, suggesting that additional factors may be involved in the repression of p21 by c-jun. Furthermore, c-jun could inhibit butyrate-inducing p21 gene expression through Sp1, indicating at least one common pathway whereby p21 expression is affected by c-jun and butyrate in opposing actions. Moreover, the hyperphosphorylated retinoblastoma protein (Rb) increased in c-jun expressing cells, indicating that phosphorylated Rb may play a role in regulating Sp1 to repress p21 expression. This is the first demonstration of how housekeeping factors and oncogene product counteract the function of tumor suppressor genes to control cell cycle progression.

Inhibition of Myc-dependent apoptosis by eukaryotic translation initiation factor 4E requires cyclin D1

Ectopically expressed eukaryotic translation initiation factor 4E (eIF4E) stimulates cell proliferation, suppresses apoptosis in growth factor restricted cells, and induces malignant transformation in primary rodent fibroblasts when coexpressed with protooncogene myc. We report here that eIF4E rescued rat embryo fibroblasts ectopically expressing c-Myc (REF/Myc) from genotoxic and non-genotoxic cytostatic drugs and identify cyclin D1 as a downstream effector in the antiapoptotic mechanism. In clones of REF/Myc ectopically expressing eIF4E, resistance to apoptosis paralleled steady state levels of cyclin D1. Stable expression of cyclin D1 in REF/Myc inhibited apoptosis in response to a broad range of cell cycle specific cytostatic agents. Partial loss-of-cyclin D1 function in REF/Myc ectopically expressing eIF4E (REF/Myc/4E) significantly increased chemosensitivity; either soluble antisense cyclin D1 oligomers or transfection with a dominant negative cyclin D1 mutant that prevents translocation of cyclin D-dependent kinases to the nucleus, significantly blunted the antiapoptotic effect of eIF4E. These data directly link eIF4E rescue from cytostatic drugs to cyclin D1. Since overexpression of eIF4E and cyclin D1 is observed in many aggressive forms of chemoresistant cancers, these findings provide insight into possible mechanisms responsible for this biological behavior.

Cyclin kinase inhibitor p21CIP1/WAF1 limits interstitial cell proliferation following ureteric obstruction

Tubulointerstitial renal injury induced by unilateral ureteric obstruction (UUO) is characterized by marked cell proliferation and apoptosis. Proliferation requires cell cycle transit that is positively regulated by cyclins and cyclin-dependent kinases (CDKs) and inhibited by the CIP/KIP family of cyclin-dependent kinase inhibitors (CKIs: p21, p27, and p57). We have shown that the absence of p27 results in markedly increased tubular epithelial cell proliferation and apoptosis following UUO (V. Ophascharoensuk, M. L. Fero, J. Hughes, J. M. Roberts, and S. J. Shankland. Nat. Med. 4: 575-580, 1998). Since p21 mRNA is upregulated following UUO, we hypothesized that p21 would also serve to limit cell proliferation and apoptosis. We performed UUO in p21 +/+ and p21 -/- mice. Cell proliferation [bromodeoxyuridine (BrdU), proliferating cell nuclear antigen (PCNA)], apoptosis [terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) method], interstitial myofibroblast accumulation (actin), macrophage infiltration (F4/80), and collagen I expression were quantified at days 3, 7, and 14. In contrast to p27 -/- mice, there was no difference in tubular epithelial cell proliferation or apoptosis between p21 -/- and p21 +/+ mice at any time point. However, interstitial cell proliferation at day 3 was significantly increased in p21 -/- mice [BrdU, 40.7 +/- 1.9 cells/high-power field (cells/hpf) vs. 28.8 +/- 2, P < 0.005], although, interestingly, no difference was seen in interstitial cell apoptosis. Actin/BrdU double staining demonstrated increased interstitial myofibroblast proliferation at day 3 in p21 -/- animals (10 +/- 0.12 vs. 5.8 +/- 0. 11 cells/hpf, P < 0.05), which was followed by increased myofibroblast accumulation at day 7 in p21 -/- mice. No differences were detected in interstitial macrophage infiltration, collagen I deposition or transforming growth factor-beta1 mRNA (in situ hybridization) expression. In conclusion p21, unlike p27, is not essential for the regulation of tubular epithelial cell proliferation and apoptosis following UUO, but p21 levels do serve to limit the magnitude of the early myofibroblast proliferation. This study demonstrates a differential role for the CKI p21 and p27 in this model.

DNA damage and p21(WAF1/CIP1/SDI1) in experimental injury of the rat adrenal cortex and trauma-associated damage of the human adrenal cortex

In vivo models are needed to study the reactions of tissues to DNA damage, such as the induction of the cyclin-dependent kinase inhibitor p21, indicating potential repair of the damage, versus apoptosis, indicating the elimination of the damaged cells. Damage to DNA occurs in tissues during shock, sepsis, and other critical medical conditions. Previous studies have found evidence of damage to the cortex of adrenal glands from organ donors who had undergone severe trauma prior to death. The present experiment studied rats under experimental interventions of clinical relevance to patients with conditions that put them at risk for damage to the adrenal glands. These interventions comprised ischaemia and reperfusion injury, sepsis following caecal ligation and puncture, acute pancreatitis, and administration of chemical agents (zymosan and acrylonitrile). All the interventions caused an increase in p21 mRNA as assessed by northern blotting and in situ hybridization. Increased nuclear p21 protein was shown by immunohistochemistry. All the interventions caused damage to DNA, as shown by labelling of available 3' termini of single-strand breaks with terminal transferase. The number of cells undergoing apoptosis, visualized by ligation of a hairpin oligonucleotide probe to double-strand breaks in DNA, was much lower. In rat adrenal glands, apoptotic cells were infrequent under all the conditions studied. They were more abundant in human organ donor adrenal glands that were previously shown to have extensive DNA damage accompanied by induction of p21. The similarity of the effects of a wide variety of surgical interventions and chemical agents suggest a common pathophysiological mechanism which is not specific to the initiating injury. Experimental injury of the rat adrenal cortex provides a model for investigating the role of organ DNA damage and of mediators of the response to DNA damage, such as p21.

Cancer dormancy and cell signaling: induction of p21(waf1) initiated by membrane IgM engagement increases survival of B lymphoma cells

The p21(WAF1) (p21) cyclin-dependent kinase inhibitor plays a major role in regulating cell cycle arrest. It was recently reported that the p53-independent elevation of p21 protein levels is essential in mediating the G(1) arrest resulting from signal transduction events initiated by the crosslinking of membrane IgM on Daudi Burkitt lymphoma cells. Although the role of p21 in cell cycle regulation is well documented, there is little information concerning its role in antibody-mediated apoptosis. In the present study, we examined the involvement of p21 in the regulation of apoptosis by suppressing its induction in anti-IgM-treated Daudi cells through a p21 antisense expression construct approach. Reduction in induced p21 protein levels resulted in diminished G(1) arrest and increased apoptosis. The increased susceptibility to anti-IgM-mediated apoptosis was associated with increased caspase-3-like activity and poly-(ADP)ribose polymerase cleavage. These data suggest that p21 may directly interfere with the caspase cascade, thus playing a dual role in regulating both cell cycle progression and apoptosis.

Effect of p21waf1/cip1 transgene on radiation induced apoptosis in T cells

The cyclin kinase inhibitor p21WAF1/Cip1 is upregulated by the tumor suppressor p53. While p21 is central for the G-1 arrest mediated by p53, it is still unclear if p21 also functions as a downstream effector of p53 dependent apoptosis. Apoptosis induced by DNA damage but not dexamethasone is p53 dependent in thymocytes. To investigate the physiological role of p21 in apoptosis, we have generated transgenic mice in which the p21 transgene is targeted for restricted expression in the T cell lineage. Thymocytes from p21 transgenic mice were hypersensitive to cell death induced by DNA damaging agents such as ionizing radiation and UV, but not be dexamethasone. Irradiated p21 transgenic thymocytes had approximately twofold more apoptotic cells as compared to irradiated age matched littermate control mice. Radiation induced death is comparable in thymocytes from p21 + Bcl2 + double transgenic mice and age matched littermate controls, indicating that the Bcl2 transgene rescues the radiation hypersensitivity imposed by p21. However, thymocytes from p53-/- mice even when they expressed the p21 transgene, were resistant to death induced by radiation. Together these results show that thymocytes from p21 transgenic mice are hypersensitive to radiation induced programmed cell death and suggest that the radiation hypersensitivity of p21 transgenic thymocytes involves p53 dependent pathway and signals in addition to p21.

Adenovirus-mediated p21((WAF1/SDII/CIP1)) gene transfer induces apoptosis of human cervical cancer cell lines

p21((WAF1/SDII/CIP1)) (p21) arrests cell growth by inhibiting cyclin-depend kinases. To explore the potential of using p21 for the gene therapy of cervical cancer, we infected human papillomavirus (HPV)-positive cervical cancer cells (HeLa, SiHa, and Z172) and HPV-negative cervical cancer cells (C33A) with recombinant adenovirus encoding p21 cDNA. The results revealed that effective inhibition of cell growth could be achieved by sense p21 adenovirus but not antisense p21 adenovirus infection and occurred through apoptosis as measured by DNA fragmentation and chromatin condensation. Apoptosis was also observed in xenografts of human cervical cancer cells infected with sense p21 adenovirus, as confirmed by in situ terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling (TUNEL). The apoptosis was not prevented by overexpression of the bcl-2 transgene. To sum up, the apoptotic effect suggests that p21 should be a tumoricidal agent instead of a tumoristatic agent in preventing cervical cancers. In addition, our report substantiates the combination of the high efficiency of adenovirus vector-mediated gene delivery and the apoptotic effect of p21.

p21Waf1/Cip1/Sdi1 induces permanent growth arrest with markers of replicative senescence in human tumor cells lacking functional p53

We have shown previously that wild type p53 can rapidly induce replicative senescence in EJ human bladder carcinoma cells lacking functional p53. A major effector of p53 functions is p21Waf1/Cip1/Sdi1, a potent cyclin-dependent kinase inhibitor. p21Waf1/Cip1/Sdi1 has been shown to be involved in both p53 dependent and independent control of cell proliferation, differentiation and death. To directly investigate the effects of p21Waf1/Cip1/Sdi1 in the p53 response observed in EJ tumor cells, we established p21Waf1/Cip1/Sdi1 inducible lines using the tetracycline-regulatable vector system. p21Waf1/Cip1/Sdi1 induction caused irreversible cell cycle arrest in both G1 and G2/M, and diminished Cdk2 kinase activity. In addition, p21Waf1/Cip1/Sdi1 induction led to morphological alterations characteristic of cells undergoing replicative senescence with morphological, biochemical and ultrastructural markers of the senescent phenotype. Furthermore, sustained p21Waf1/Cip1/Sdi1 induction sensitized EJ cells to apoptotic cell death induced by mitomycin C, a cross-linking DNA damaging agent. These findings support the function of p21Waf1/Cip1/Sdi1 as an inducer of replicative senescence and a major mediator of this phenomenon in response to p53. Moreover, our results imply that therapeutic intervention in human cancers might be aimed at sustained elevation of p21Waf1/Cip1/Sdi1 expression.

Transforming growth factor beta1 rescues serum deprivation-induced apoptosis via the mitogen-activated protein kinase (MAPK) pathway in macrophages

Cell death and cell survival are central components of normal development and pathologic states. Transforming growth factor beta1 (TGF-beta1) is a pleiotropic cytokine that regulates both cell growth and cell death. To better understand the molecular mechanisms that control cell death or survival, we investigated the role of TGF-beta1 in the apoptotic process by dominant-negative inhibition of both TGF-beta1 and mitogen-activated protein kinase (MAPK) signaling pathways. Murine macrophages (RAW 264.7) undergo apoptosis following serum deprivation, as determined by DNA laddering assay. However, apoptosis is prevented in serum-deprived macrophages by the presence of exogenous TGF-beta1. Using stably transfected RAW 264.7 cells with the kinase-deleted dominant-negative mutant of TbetaR-II (TbetaR-IIM) cDNA, we demonstrate that this protective effect by TGF-beta1 is completely abrogated. To determine the downstream signaling pathways, we examined TGF-beta1 effects on the MAPK pathway. We show that TGF-beta1 induces the extracellular signal-regulated kinase (ERK) activity in a time-dependent manner up to 4 h after stimulation. Furthermore, TGF-beta1 does not rescue serum deprivation-induced apoptosis in RAW 264.7 cells transfected with a dominant-negative mutant MAPK (ERK2) cDNA or in wild type RAW 264.7 cells in the presence of the MAPK kinase (MEK1) inhibitor. Taken together, our data demonstrate for the first time that TGF-beta1 is an inhibitor of apoptosis in cultured macrophages and may serve as a cell survival factor via TbetaR-II-mediated signaling and downstream intracellular MAPK signaling pathway.

Abrogation of cyclin D1 expression predisposes lung cancer cells to serum deprivation-induced apoptosis

Cyclin D1 antisense (D1AS)-transfected lung epithelial cell lines were serum deprived and then analyzed for three hallmarks of apoptosis: appearance of single-strand DNA breaks, alteration of apoptosis-related protein expression, and induction of chromatin condensation. Single-strand DNA breaks appeared at significant levels 24 h after serum deprivation, whereas induction of chromatin condensation was observed after 72 h. The antioxidants dimethyl sulfoxide, ascorbate, and glutathione, as well as insulin-like growth factor-I, inhibited induction of DNA damage in this assay. Additionally, proliferating cell nuclear antigen expression is completely suppressed in the D1AS cells, indicating a mechanism to explain the reduced capacity for DNA repair. Increased expression of cyclin D1, which is a common lesion in lung cancer, may thus prevent induction of apoptosis in an oxidizing and growth factor-poor environment. Reducing cyclin D1 expression in lung cancer cells by expression of D1AS RNA disrupted these protective pathways.

p27Kip1 induces drug resistance by preventing apoptosis upstream of cytochrome c release and procaspase-3 activation in leukemic cells

The cyclin-dependent kinase inhibitor p27Kip1 has been implicated as a drug resistance factor in tumor cells grown as spheroids or confluent monolayers. Here, we show that p27Kip1 overexpression also induces resistance to drug-induced apoptosis and cytotoxicity in human leukemic cells growing in suspension. The anti-apoptotic effect of p27Kip1 is not restricted to DNA-damaging agents but extends to the tubulin poison vinblastin, agonistic anti-Fas antibodies and macromolecule synthesis inhibitors. To further identify at which level this protein interferes with the cell death pathway, we investigated its influence on caspase activation and mitochondrial changes. Exposure of mock-transfected U937 cells to 50 microm etoposide activates procaspase-3 and the long isoform of procaspase-2 and induces mitochondrial potential decrease and cytochrome c release from mitochondria to the cytosol. All these events are prevented by p27Kip1 overexpression. p27Kip1 does not modulate Bcl-2, Bcl-X(L), Mcl-1 and Bax protein level in leukemic cells but suppresses Mcl-1 expression decrease observed in mock-transfected U937 cells undergoing etoposide-induced cell death. We conclude that p27Kip1 prevents cell death upstream of the final pathway common to many apoptotic stimuli that involves cytochrome c release from mitochondria and activation of downstream caspases.

Volatile fatty acid, metabolic by-product of periodontopathic bacteria, induces apoptosis in WEHI 231 and RAJI B lymphoma cells and splenic B cells

The ability of butyric acid, an extracellular metabolite from periodontopathic bacteria, to induce apoptosis in murine WEHI 231 cells, splenic B cells, and human RAJI cells was examined. The culture filtrate of Porphyromonas gingivalis, Prevotella loescheii, and Fusobacterium nucleatum, which contains high a percentage of butyric acid, induced DNA fragmentation in WEHI 231 cells. Volatile fatty acid, especially butyric acid, significantly suppressed B-cell viability in a concentration-dependent fashion. The DNA fragmentation assay indicated that butyric acid rapidly induced apoptosis in WEHI 231 cells (with 1.25 mM butyric acid and 6 h after treatment), splenic B cells (with 1.25 mM butyric acid), and RAJI cells (with 2.5 mM butyric acid). Incubation of WEHI 231 cells with butyric acid for 16 h resulted in the typical ladder pattern of DNA fragmentation and the apoptoic change such as chromatin condensation and hypodiploid nuclei. Cell cycle analysis implied that butyric acid arrested the cells at the G1 phase. The inhibitory assay suggested that butyric acid-induced apoptosis of WEHI 231 and splenic B cells was inhibited by W-7, a calmodulin inhibitor. These results suggest that calmodulin-dependent regulation is involved in the signal transduction pathway of butyric acid.

Apoptosis and DNA damage in type 2 alveolar epithelial cells cultured from hyperoxic rats

Apoptosis is a genetically controlled cellular response to developmental stimuli and environmental insult that culminates in cell death. Sublethal hyperoxic injury in rodents is characterized by a complex but reproducible pattern of lung injury and repair during which the alveolar surface is damaged, denuded, and finally repopulated by type 2 alveolar epithelial cells (AEC2). Postulating that apoptosis might occur in AEC2 after hyperoxic injury, we looked for the hallmarks of apoptosis in AEC2 from hyperoxic rats. A pattern of increased DNA end labeling, DNA laddering, and induction of p53, p21, and Bax proteins, strongly suggestive of apoptosis, was seen in AEC2 cultured from hyperoxic rats when compared with control AEC2. In contrast, significant apoptosis was not detected in freshly isolated AEC2 from oxygen-treated rats. Thus the basal culture conditions appeared to be insufficient to ensure the ex vivo survival of AEC2 damaged in vivo. The oxygen-induced DNA strand breaks were blocked by the addition of 20 ng/ml of keratinocyte growth factor (KGF) to the culture medium from the time of plating and were partly inhibited by Matrigel or a soluble extract of Matrigel. KGF treatment resulted in a partial reduction in the expression of the p21, p53, and Bax proteins but had no effect on DNA laddering. We conclude that sublethal doses of oxygen in vivo cause damage to AEC2, resulting in apoptosis in ex vivo culture, and that KGF can reduce the oxygen-induced DNA damage. We speculate that KGF plays a role as a survival factor in AEC2 by limiting apoptosis in the lung after acute hyperoxic injury.

Inhibition of growth of human vascular smooth muscle cells by overexpression of p21 gene through induction of apoptosis

The senescent cell-derived inhibitor (sdi)-1 protein (p21 product) has been identified as a downstream mediator of the tumor suppressor p53 in the regulation of cell cycle progression through a G1 phase checkpoint. Given the importance of cell cycle inhibition for the treatment of restenosis, in this study we focused on the function of p21 gene in inhibiting proliferation of vascular smooth muscle cells (VSMC). To test the hypothesis, we transfected human p21 gene into human aortic VSMC using hemagglutinating virus of Japan-liposome-mediated transfer. Initially, we examined the successful transfection of human p21 gene into VSMC. p21 protein was increased in VSMC transfected with p21 vector as compared with control vector. Accompanied by increased p21 protein, transfection of p21 vector resulted in a significant decrease in number of VSMC induced by 2% serum (P<.01). Although p21 has been reported to play an important role in the regulation of apoptosis in some cells, apoptosis mediated by p21 is still controversial. Therefore, we hypothesized that overexpression of p21 mediates apoptosis in human VSMC, in addition to the blockade of cell cycle progression. First, we assessed the concordance between morphologic analysis and apoptosis as determined by nuclear staining with Hoechst 33342. Cells transfected with p21 gene exhibited the characteristic features of cell shrinkage, membrane blebbing, and rounding that are typical of apoptotic death. Of greater interest, a significant increase in apoptotic cells was observed in VSMC transfected with p21 vector as compared with control vector (P<.01). These results were confirmed by the measurement of DNA fragmentation. Consistent with nuclear staining, DNA fragmentation in VSMC transfected with human p21 gene was significantly increased as compared with that in VSMC transfected with control vector (P<.05). To study the molecular mechanisms of apoptosis mediated by overexpression of p21 gene, the protein levels of bax, a promoter of apoptosis, and bcl-2, an inhibitor of apoptosis, were also measured by Western blotting. Overexpression of p21 gene significantly increased protein of bax (P<.05), whereas transfection of p21 gene did not alter bcl-2 protein. Importantly, the ratio of bax to bcl-2 was significantly increased in VSMC transfected with human p21 vector as compared with control vector (P<.05). Overall, these results demonstrated that inhibition of VSMC growth by overexpression of human p21 gene was accompanied by induction of apoptosis through an inappropriate increase in bax protein. These results suggest that regulation of cell cycle by p21 may be closely linked to programmed cell death/apoptosis in human VSMC.