Epidermal growth factor induces Gadd45 (growth arrest and DNA damage inducible protein) expression in A431 cells

Expression of p21 and p53 in rat gingival and human oral epithelial cells after cyclosporine A treatment

BACKGROUND AND OBJECTIVE

Expression of p21 and p53 were examined, at gene and protein levels, in edentulous gingival epithelial cells from rats and from a human oral epidermoid carcinoma cell line, OECM1, after cyclosporine A therapy.

MATERIAL AND METHODS

In vivo: 20 partially edentulous SD rats were assigned into cyclosporine A feeding and control groups. After the rats were killed, p21 and p53 in gingiva were evaluated by reverse transcription-polymerase chain reaction and immunohistochemistry. In vitro: after cyclosporine A treatment, p21 and p53 of OECM1 cells were evaluated by western blot and the luciferase assay. The distribution of OECM1 cells in each phase of the cell cycle was evaluated by flow cytometry.

RESULTS

The mRNA expression of p21 was significantly higher in the cyclosporine A group than in the control group. A greater number of positive anti-p21-stained cells were observed in the gingival epithelium of the cyclosporine A group than in the control group. Significantly higher levels of p21 protein and activity were observed in OECM1 cells after cyclosporine A treatment than in cells without treatment. A relative increase of cells in G0/G1 phases, and a decrease of cells in G2/M phases, were observed in OECM1 cells after cyclosporine A treatment.

CONCLUSION

In the present study, higher p21 mRNA and protein expressions were observed after cyclosporine A treatment. Thus, an up-regulation of p21 expression, via a p53-independent pathway, by cyclosporine A in gingival and oral epithelial cells was suggested.

Transcriptional signature of epidermal keratinocytes subjected to in vitro scratch wounding reveals selective roles for ERK1/2, p38, and phosphatidylinositol 3-kinase signaling pathways

Covering denuded dermal surfaces after injury requires migration, proliferation, and differentiation of skin keratinocytes. To clarify the major traits controlling these intermingled biological events, we surveyed the genomic modifications occurring during the course of a scratch wound closure of cultured human keratinocytes. Using a DNA microarray approach, we report the identification of 161 new markers of epidermal repair. Expression data, combined with functional analysis performed with specific inhibitors of ERK, p38(MAPK) and phosphatidylinositol 3-kinase (PI3K), demonstrate that kinase pathways exert very selective functions by precisely controlling the expression of specific genes. Inhibition of the ERK pathway totally blocks the wound closure and inactivates many early transcription factors and EGF-type growth factors. p38(MAPK) inhibition only delays "healing," probably in line with the control of genes involved in the propagation of injury-initiated signaling. In contrast, PI3K inhibition accelerates the scratch closure and potentiates the scratch-dependent stimulation of three genes related to epithelial cell transformation, namely HAS3, HBEGF, and ETS1. Our results define in vitro human keratinocyte wound closure as a repair process resulting from a fine balance between positive signals controlled by ERK and p38(MAPK) and negative ones triggered by PI3K. The perturbation of any of these pathways might lead to dysfunction in the healing process, similar to those observed in pathological wounding phenotypes, such as hypertrophic scars or keloids.

Effect of reduced EGFR function on the radiosensitivity and proliferative capacity of mouse jejunal crypt clonogens

BACKGROUND AND PURPOSE

Previous data indicate that the EGFR pathway is involved in the response of tumor cell lines to irradiation. To determine if this receptor plays a role in the response of the intestinal mucosa, the effect of a spontaneous mutation in EGFR (B6C3-a-wa-2) on radiosensitivity and proliferative capacity was investigated using in vivo clonogenic assays and immunohistochemistry.

PATIENTS AND METHODS

EGFR mutant mice were compared with wild-type mice using the in vivo jejunal microcolony assay using single and split doses to measure the radiosensitivity and repopulation of clonogenic jejunal mucosal cells. In addition, paraffin-embedded tissue sections were assessed for proliferation (PCNA), DNA repair (Ku70 and gamma H2AX), and apoptosis (TUNEL) by immunofluorescent staining (wild-type vs. heterozygous only) at various times after 5 Gy single dose.

RESULTS

After the high doses used in the split-dose experiments, EGFR heterozygous and homozygous mutant mice were significantly more radiosensitive than their wild-type littermates. There was no clear difference in split-dose repair based on EGFR function. After 5 Gy single dose there were significantly more apoptotic cells within the crypts of heterozygous mice than of wild-type mice, beginning at 3h post irradiation. Decreased proliferation was observed only in the homozygous mutant mice. PCNA staining was lower in the heterozygous mice than in wild-type mice at 1 and 3 h post-5 Gy.

CONCLUSION

The results indicate that after high doses the radiosensitivity of EGFR mutant mice is significantly higher than that of wild-type, and that this could be the result of an increase in apoptosis rather than reduced DNA repair. Proliferative capacity was modestly reduced, but only in the homozygous mutants.

Exogenous Fibroblast Growth Factors Maintain Viability, Promote Proliferation, and Suppress GADD45α and GAS6 Transcript Content of Prostate Cancer Cells Genetically Modified to Lack Endogenous FGF-2

Understanding processes regulating prostate cancer cell survival is critical to management of advanced disease. We used prostate cancer cell transfectants genetically modified to be deficient in either endogenous fibroblast growth factor (FGF-1) or endogenous FGF-2 to examine FGF maintenance of transfectant survival and proliferation and FGF-2-regulated expression of transfectant growth arrest DNA damage (GADD) and growth arrest sequences (GAS) family genes (known modulators of cell cycle progression and survival) and the AS3 gene (an androgen-modulated effector of prostate cell proliferation). When propagated in the absence of exogenous FGFs, FGF-2-deficient transfectants undergo exponential death, whereas FGF-1-deficient transfectants proliferate. Exogenous FGF-1, FGF-2, FGF-7, or FGF-8 promote survival and proliferation of FGF-2-deficient transfectants and enhance FGF-1-deficient transfectant proliferation. Transfectants express FGF receptor FGFR1, FGFR2(IIIb), FGFR2(IIIc), and FGFR3 transcripts, findings consistent with the effects of exogenous FGFs. FGF-2-deficient transfectants express high levels of AS3, GADD45α, GADD45γ, GAS8, and GAS11 transcripts and moderate levels of GADD153, GAS2, GAS3, and GAS6 transcripts and lack demonstrable GAS1 or GAS5 transcripts. FGF withdrawal-mediated death of FGF-2-deficient transfectants did not significantly affect cell AS3, GADD153, GADD45γ, GAS2, GAS3, GAS7, GAS8, or GAS11 transcript content, whereas GADD45α and GAS6 transcript content was elevated. These studies establish that endogenous FGF-2 dominantly regulates prostate cancer cell survival and proliferation and that exogenous FGFs may assume this function in the absence of endogenous FGF-2. Additionally, we provide the first evidence that FGFs regulate prostate GADD45α and GAS6 transcript content. The latter observations suggest that GADD45α and GAS6 proteins may be effectors of processes that regulate prostate cancer cell survival. Additional studies are required to examine this possibility in detail.

Effects of Tumor Necrosis Factor-α (TNFα) in Epidermal Keratinocytes Revealed Using Global Transcriptional Profiling

Identification of tumor necrosis factor-alpha (TNF alpha) as the key agent in inflammatory disorders, e.g. rheumatoid arthritis, Crohn's disease, and psoriasis, led to TNF alpha-targeting therapies, which, although avoiding many of the side-effects of previous drugs, nonetheless causes other side-effects, including secondary infections and cancer. By controlling gene expression, TNF alpha orchestrates the cutaneous responses to environmental damage and inflammation. To define TNF alpha action in epidermis, we compared the transcriptional profiles of normal human keratinocytes untreated and treated with TNF alpha for 1, 4, 24, and 48 h by using oligonucleotide microarrays. We found that TNF alpha regulates not only immune and inflammatory responses but also tissue remodeling, cell motility, cell cycle, and apoptosis. Specifically, TNF alpha regulates innate immunity and inflammation by inducing a characteristic large set of chemokines, including newly identified TNF alpha targets, that attract neutrophils, macrophages, and skin-specific memory T-cells. This implicates TNF alpha in the pathogenesis of psoriasis, fixed drug eruption, atopic and allergic contact dermatitis. TNF alpha promotes tissue repair by inducing basement membrane components and collagen-degrading proteases. Unexpectedly, TNF alpha induces actin cytoskeleton regulators and integrins, enhancing keratinocyte motility and attachment, effects not previously associated with TNF alpha. Also unanticipated was the influence of TNF alpha upon keratinocyte cell fate by regulating cell-cycle and apoptosis-associated genes. Therefore, TNF alpha initiates not only the initiation of inflammation and responses to injury, but also the subsequent epidermal repair. The results provide new insights into the harmful and beneficial TNF alpha effects and define the mechanisms and genes that achieve these outcomes, both of which are important for TNF alpha-targeted therapies.

Reversal of multidrug resistance in cancer cells by pyranocoumarins isolated from Radix Peucedani

The pyranocoumarins, (+/-)-3'-angeloyl-4'-acetoxy-cis-khellactone, were isolated from Radix Peucedani, the dry root of Peucedanum praeruptorum Dunn, through bioassay-guided fractionation. The chemical structure of pyranocoumarins was determined by mass spectrometry and nuclear magnetic resonance (NMR) spectroscopy. X-ray crystallography showed that there are eight molecules (i.e. two each of four conformers) in each unit cell with their optical activities equally cancelled out. The four conformers are 3'(R)-angeloyl-4'(R)-acetoxy-khellactone in two conformational forms, and 3'(S)-angeloyl-4'(S)-acetoxy-khellactone in two conformational forms. Pyranocoumarins caused apoptotic cell death with IC50 of 41.9+/-2.8 and 17.3+/-8.2 microM for drug-sensitive KB-3-1 and multidrug resistant (MDR) KB-V1, respectively. The two- to threefold sensitivity difference between the two cell lines is interesting considering that the same ratio for doxorubicin is 50-300. Strong synergistic interactions were demonstrated when pyranocoumarins were combined with common anti-tumor drugs including doxorubicin, paclitaxel, puromycin or vincristine in MDR KB-V1 cell line, but not in drug-sensitive KB-3-1 cells. Pyranocoumarins increased doxorubicin accumulation in KB-V1 cells by about 25% after 6 h of incubation. Pyranocoumarins treatment for 24 h down-regulated the expression of P-glycoprotein in KB-V1 cells at both protein and mRNA levels. Pyranocoumarins also transiently reduced the cellular ATP contents in KB-V1 cells in a dose-dependent manner. Our results suggest that pyranocoumarins could be a potential MDR reversing agent.

Role of Gadd45alpha in the density-dependent G1 arrest induced by p27(Kip1)

p27(Kip1), an inhibitor of cyclin-dependent kinases, is an important regulator of cell cycle progression. We have previously shown that p27(Kip1) inhibits the G0 to S transition when ectopically expressed in p27-47 mouse fibroblasts arrested at high but not low densities. In the study described here, we identify Gadd45alpha, a member of the growth arrest- and DNA damage-inducible family of proteins, as a potential mediator of the density-dependent effects of p27(Kip1) on cell proliferation. Gadd45alpha mRNA and protein were more abundant in p27-47 cells arrested at high densities than at low densities. Amounts of both decreased and remained low when cells arrested at high densities were exposed to mitogens in the absence, but not in the presence, of ectopically expressed p27(Kip1). Importantly, enforced expression of Gadd45alpha prevented density-arrested mouse fibroblasts from initiating DNA synthesis in response to mitogens. We suggest that amounts of Gadd45alpha above a certain threshold are growth inhibitory and that such amounts are achieved in cells arrested at high but not low densities. For cultures arrested at high densities, the resumption of cell cycle traverse requires a sustained reduction in Gadd45alpha abundance, a process that is induced by mitogens and inhibited by p27(Kip1).

Stress and radiation-induced activation of multiple intracellular signaling pathways

Exposure of cells to a variety of stresses induces compensatory activations of multiple intracellular signaling pathways. These activations can play critical roles in controlling cell survival and repopulation effects in a stress-specific and cell type-dependent manner. Some stress-induced signaling pathways are those normally activated by mitogens such as the EGFR/RAS/PI3K-MAPK pathway. Other pathways activated by stresses such as ionizing radiation include those downstream of death receptors, including pro-caspases and the transcription factor NFKB. This review will attempt to describe some of the complex network of signals induced by ionizing radiation and other cellular stresses in animal cells, with particular attention to signaling by growth factor and death receptors. This includes radiation-induced signaling via the EGFR and IGFI-R to the PI3K, MAPK, JNK, and p38 pathways as well as FAS-R and TNF-R signaling to pro-caspases and NFKB. The roles of autocrine ligands in the responses of cells and bystander cells to radiation and cellular stresses will also be discussed. Based on the data currently available, it appears that radiation can simultaneously activate multiple signaling pathways in cells. Reactive oxygen and nitrogen species may play an important role in this process by inhibiting protein tyrosine phosphatase activity. The ability of radiation to activate signaling pathways may depend on the expression of growth factor receptors, autocrine factors, RAS mutation, and PTEN expression. In other words, just because pathway X is activated by radiation in one cell type does not mean that pathway X will be activated in a different cell type. Radiation-induced signaling through growth factor receptors such as the EGFR may provide radioprotective signals through multiple downstream pathways. In some cell types, enhanced basal signaling by proto-oncogenes such as RAS may provide a radioprotective signal. In many cell types, this may be through PI3K, in others potentially by NFKB or MAPK. Receptor signaling is often dependent on autocrine factors, and synthesis of autocrine factors will have an impact on the amount of radiation-induced pathway activity. For example, cells expressing TGFalpha and HB-EGF will generate protection primarily through EGFR. Heregulin and neuregulins will generate protective signals through ERBB4/ERBB3. The impact on radiation-induced signaling of other autocrine and paracrine ligands such as TGFbeta and interleukin 6 is likely to be as complicated as described above for the ERBB receptors.

p38 mitogen-activated protein kinase-independent induction of gadd45 expression in nerve growth factor-induced apoptosis in medulloblastomas

We describe a novel nerve growth factor (NGF)-signaling pathway leading to gadd45 induction that is independent of JNK and p38 MAPK. We used cDNA arrays representing 588 genes to investigate the role of differential gene expression in NGF-mediated pleiotropic responses. We compared the gene expression profiles obtained from MED283-TrkA cells undergoing NGF-induced apoptosis to PC12 cells undergoing NGF-induced differentiation. An early and specific transcriptional target of NGF in MED283-TrkA cells was the DNA-damage-inducible gene gadd45. Its magnitude of induction directly correlated with the magnitude of apoptosis in MED283 clones transfected with mutant TrkA receptors. Although gadd45 has been implicated in stress response signaling, in vitro kinase assays indicated that NGF neither activated c-Jun NH2-terminal kinase (JNK) nor p38 mitogen-activated protein kinase (MAPK). Furthermore, the p38 MAPK inhibitor SB203580 (20 microM) failed to prevent NGF-induced apoptosis and NGF-induced gadd45 expression. These results suggest that differential regulation of gadd45 expression possibly through BRCA1 may be a potential mechanism whereby NGF regulates pleiotropic responses.

PKCdelta-dependent deubiquitination and stabilization of Gadd45 in A431 cells overexposed to EGF

Epidermal growth factor (EGF) receptor-overexpressing p53-deficient A431 cells response to toxic dose of EGF by G1 arrest and apoptosis was studied. We previously reported an increased expression of growth arrest and DNA-damage-inducible gene, Gadd45, in EGF-overexposed A431 cells. The mechanism for this induction was increased half-lives of mRNA and protein. In this study, using phorbol ester (a PKC activator) and specific inhibitors of PKC isoforms, we showed that protein kinase C-delta (PKCdelta) was involved in the increase of Gadd45 protein stability. We further demonstrated that Gadd45 is ubiquitinated and is regulated by proteolysis. While EGF induced ubiquitination of total cellular proteins, there was a decrease in Gadd45 ubiquitination, which could be inhibited by Rottlerin, a PKCdelta-specific inhibitor. These results suggest that an increase in Gadd45 stability may involve PKCdelta-dependent ubiquitin-proteasome pathway.