K-ras p21 expression and activity in lung and lung tumors

Repression of BCL2 by the tumor suppressor activity of the lysyl oxidase propeptide inhibits transformed phenotype of lung and pancreatic cancer cells

The gene encoding lysyl oxidase (LOX) was identified as the ras recision gene (rrg), with the ability to revert Ras-mediated transformation of NIH 3T3 fibroblasts. Mutations in RAS genes have been found in approximately 25% of lung cancers and in 85% of pancreatic cancers. In microarray analysis, these cancers were found to display reduced LOX gene expression. Thus, the ability of the LOX gene to repress the transformed phenotype of these cancer cells was tested. LOX is synthesized as a 50-kDa secreted precursor Pro-LOX that is processed to the 32-kDa active enzyme (LOX) and to an 18-kDa propeptide (LOX-PP). Recently, we mapped the rrg activity of Pro-LOX to the LOX-PP in Ras-transformed NIH 3T3 cells. Ectopic Pro-LOX and LOX-PP expression in H1299 lung cancer cells inhibited growth in soft agar and invasive colony formation in Matrigel and reduced activation of extracellular signal-regulated kinase (ERK) and Akt, with LOX-PP showing substantially higher activity. Similarly, LOX-PP expression in PANC-1 pancreatic cancer cells effectively reduced ERK and Akt activity and inhibited growth in soft agar and ability of these cells to migrate. Nuclear Factor-kappaB (NF-kappaB) and its target gene BCL2, which are overexpressed in 70% to 75% of pancreatic cancers, have recently been implicated in invasive phenotype. LOX-PP substantially reduced NF-kappaB and Bcl-2 levels. Reintroduction of Bcl-2 into PANC-1 or H1299 cells expressing LOX-PP restored the transformed phenotype, suggesting that Bcl-2 is an essential target. Thus, LOX-PP potently inhibits invasive phenotype of lung and pancreatic cancer cells, suggesting potential therapeutic applications in treatment of these cancers.

Targeting receptor tyrosine kinase signalling in small cell lung cancer (SCLC): what have we learned so far?

Small cell lung cancer (SCLC) is an aggressive form of lung cancer, which represents 13% of all cases and is strongly associated with cigarette smoking. The survival of SCLC patients is dismal and has not greatly improved in the last 20 years, despite advances in chemotherapy regimens and a better understanding of SCLC biology. The development of resistance to chemotherapy and metastasis are commonly recognized as important causes of poor clinical outcome in SCLC. Targeting receptor tyrosine kinase (RTK) signalling represents an attractive approach to develop new drugs for SCLC, in view of the accumulating data demonstrating that polypeptide growth factors play a key role in driving SCLC cell proliferation, chemoresistance and metastasis. The insulin-like growth factor-I receptor (IGF-IR), c-Kit, vascular endothelial growth factor receptor (VEGFR) and epidermal growth factor receptor (EGFR) have been identified as potential drug targets in SCLC. Moreover, downstream signalling mediators of RTKs, such as phosphoinositide 3-kinase (PI3K)/Akt and the mammalian target of rapamycin (mTOR) may also represent attractive candidate molecules for anti-cancer therapies in SCLC. Here we will review the available data concerning results with RTK inhibitors in SCLC and the clinical trials undertaken to investigate the potential of these compounds as anti-tumour agents in SCLC.

Elevated K-ras activity with cholestyramine and lovastatin, but not konjac mannan or niacin in lung--importance of mouse strain

Our previous work established that hypocholesterolemic agents altered K-ras intracellular localization in lung. Here, we examined K-ras activity to define further its potential importance in lung carcinogenesis. K-ras activity in lungs from male A/J, Swiss and C57BL/6 mice was examined. For 3 weeks, mice consumed either 2 or 4% cholestyramine (CS), 1% niacin, 5% konjac mannan (KM), or were injected with lovastatin 25mg/kg three or five times weekly (Lov-3X and Lov-5X). A pair-fed (PF) group was fed the same quantity of diet consumed by the Lov-5X mice to control for lower body weights in Lov-5X mice. After 3 weeks, serum cholesterol was assayed with a commercial kit. Activated K-ras protein from lung was affinity precipitated with a Raf-1 ras binding domain-glutathione-S-transferase fusion protein bound to glutathione-agarose beads, followed by Western blotting, K-ras antibody treatment, and chemiluminescent detection. Only KM reduced serum cholesterol (in two of three mouse strains). In C56BL/6 mice treated with Lov-3X, lung K-ras activity increased 1.8-fold versus control (p=0.009). In normal lung with wild-type K-ras, this would be expected to be associated with maintenance of differentiation. In A/J mice fed 4% CS, K-ras activity increased 2.1-fold (p=0.02), which might be responsible for the reported enhancement of carcinogenesis in carcinogen-treated rats fed CS. KM feeding and PF treatment had no significant effects on K-ras activity. These data are consistent with the concept that K-ras in lung has an oncogenic function when mutated, but may act as a tumor suppressor when wild-type.

Transformation of human bronchial epithelial cells alters responsiveness to inflammatory cytokines

BACKGROUND

Inflammation is commonly associated with lung tumors. Since inflammatory mediators, including members of the interleukin-6 (IL-6) cytokine family, suppress proliferation of normal epithelial cells, we hypothesized that epithelial cells must develop mechanisms to evade this inhibition during the tumorigenesis. This study compared the cytokine responses of normal epithelial cells to that of premalignant cells.

METHODS

Short-term primary cultures of epithelial cells were established from bronchial brushings. Paired sets of brushings were obtained from areas of normal bronchial epithelium and from areas of metaplastic or dysplastic epithelium, or areas of frank endobronchial carcinoma. In 43 paired cultures, the signalling through the signal transducer and activator of transcription (STAT) and extracellular regulated kinase (ERK) pathways and growth regulation by IL-6, leukemia inhibitory factor (LIF), oncostatin M (OSM), interferon-gamma (IFNgamma) or epidermal growth factor (EGF) were determined. Inducible expression and function of the leukemia inhibitory factor receptor was assessed by treatment with the histone deacetylase inhibitor depsipeptide.

RESULTS

Normal epithelial cells respond strongly to OSM, IFNgamma and EGF, and respond moderately to IL-6, and do not exhibit a detectable response to LIF. In preneoplastic cells, the aberrant signaling that was detected most frequently was an elevated activation of ERK, a reduced or increased IL-6 and EGF response, and an increased LIF response. Some of these changes in preneoplastic cell signaling approach those observed in established lung cancer cell lines. Epigenetic control of LIF receptor expression by histone acetylation can account for the gain of LIF responsiveness. OSM and macrophage-derived cytokines suppressed proliferation of normal epithelial cells, but reduced inhibition or even stimulated proliferation was noted for preneoplastic cells. These alterations likely contribute to the supporting effects that inflammation has on lung tumor progression.

CONCLUSION

This study indicates that during the earliest stage of premalignant transformation, a modified response to cytokines and EGF is evident. Some of the altered cytokine responses in primary premalignant cells are comparable to those seen in established lung cancer cell lines.

Distinct and sequential upregulation of genes regulating cell growth and cell cycle progression during hepatic ischemia-reperfusion injury

Ischemia-reperfusion injury (IRI) in liver and other organs is manifested as an injury phase followed by recovery and resolution. Control of cell growth and proliferation is essential for recovery from the injury. We examined the expression of three related regulators of cell cycle progression in liver IRI: spermidine/spermine N-acetyltransferase (SSAT), p21 (a cyclin-dependent kinase inhibitor), and stathmin. Mice were subjected to hepatic IRI, and liver tissues were harvested at timed intervals. The expression of SSAT, the rate-limiting enzyme in the polyamine catabolic pathway, had increased fivefold 6 h after IRI and correlated with increased putrescine levels in the liver, consistent with increased SSAT enzymatic activity in IRI. The expression of p21, which is transactivated by p53, was undetectable in sham-operated animals but was heavily induced at 12 and 24 h of reperfusion and declined to undetectable baseline levels at 72 h of reperfusion. The interaction of the polyamine pathway with the p53-p21 pathway was shown in vitro, where activation of SSAT with polyamine analog or the addition of putrescine to cultured hepatocytes induced the expression of p53 and p21 and decreased cell viability. The expression of stathmin, which is under negative transcriptional regulation by p21 and controls cell proliferation and progression through mitosis, remained undetectable at 6, 12, and 24 h of reperfusion and was progressively and heavily induced at 48 and 72 h of reperfusion. Double-immunofluorescence labeling with antibodies against stathmin and PCNA, a marker of cell proliferation, demonstrated colocalization of stathmin and PCNA at 48 and 72 h of reperfusion in hepatocytes, indicating the initiation of cell proliferation. The distinct and sequential upregulation of SSAT, p21, and stathmin, along with biochemical activation of the polyamine catabolic pathway in IRI in vivo and the demonstration of p53-p21 upregulation by SSAT and putrescine in vitro, points to the important role of regulators of cell growth and cell cycle progression in the pathophysiology and/or recovery in liver IRI. The data further suggest that SSAT may play a role in the initiation of injury, whereas p21 and stathmin may be involved in the resolution and recovery after liver IRI.

The wild-type Ras: road ahead

The cellular Ras is known to play an important role in cellular proliferation mediated by growth factor receptor. Evidence also points to its role in growth arrest. Substantiated proof for growth-suppressive activity of wild-type Ras comes from studies that showed 1) loss of wild-type ras allele in tumors, 2) suppression of growth in cells transformed by oncogenic ras upon overexpression of wild-type Ras, and 3) up-regulation of Ras expression during postnatal development and following growth arrest of untransformed cells in culture. To understand the mechanism by which the wild-type Ras brings about these diverse actions, we evaluated its well-known role in actively proliferating cells and its less understood role in growth arrest. This led to the proposal that wild-type Ras in either GDP or GTP-bound state can antagonize the function of oncogenic Ras.-Singh, A., Sowjanya, A. P., Ramakrishna, G. The wild-type Ras: road ahead.

In vitro anti-tumor immune response induced by dendritic cells transfected with recombinant adenovirus carrying mutant k-ras genes

The specific anti-tumor immune response induced by mouse bone marrow dendritic cells (DCs) transfected with recombinant adenovirus carrying mutant k-ras genes was investigated. DCs were generated from mouse bone marrow in the presence of rmGM-CSF (3.3 ng/mL) and rmIL-4 (1.3 ng/mL) and detected by FACS, and then transfected with the recombinant adenovirus encoding mutant k-ras gene. The efficacy of transfection and T cell stimulating activity of DCs were detected. CTL activity of the mice vaccinated with DCs was observed. The results showed that DCs had dendritic veiled morphology. BmDCs highly expressed B7-1 (80%), B7-2 (77%), MHC II (70%), CD11c (65%), CD40 (70%) and CD54 (96%) with FACS, and no significant difference in the expression was observed before and after the transfection (P > 0.05). The DCs transfected by mutant k-ras gene could significantly stimulate lymphocytes proliferation as compared with those transfected by Ad-c or non-modified DCs (P < 0.05). DC vaccine transfected by mutant k-ras gene could induce CTL activity against Lewis lung cancer, but not against B16. The specific cytotoxicity against Lewis lung cancer in Ad-k-ras/12-transduced DC group was significantly higher than those in the control, vector and non-transfected DCs groups (P < 0.05). It was concluded that special antitumor response could be induced by DCs transfected with recombinant adenovirus carrying mutant k-ras genes.

Phospho-Akt overexpression in non-small cell lung cancer confers significant stage-independent survival disadvantage

PURPOSE

Akt is a signal transduction protein that plays a central role in inhibiting apoptosis in a variety of cell types including human cancer cells. In cell lines derived from human non-small cell lung cancers (NSCLCs), Akt has been shown to confer chemoresistance by inhibition of apoptosis in response to different chemotherapeutic agents including platinum-based agents, which are often the first-line therapy for NSCLCs. Only 20% to 30% of patients with NSCLC treated with chemotherapy have clinical evidence of response. The purpose of this study is to determine whether or not overexpression of activated Akt [i.e., phosphorylated Akt (pAkt)] is correlated with survival.

EXPERIMENTAL DESIGN

We studied tumors from 61 patients with NSCLC in three tissue microarrays. All patients were followed for a period of 10 years or until death. The arrays were studied immunohistochemically with antibodies against pAkt, p53, and Ki-67.

RESULTS

There was a statistically significant difference in survival between the 14 patients with strong pAkt staining and the 47 patients with weak to absent pAkt staining both by log-rank (P = 0.0416) and Breslow analysis (P = 0.0446). Difference in survival time with respect to pAkt status was also statistically significant even after accounting for stage at diagnosis (P = 0.004). Neither p53 nor Ki-67 was a statistically significant prognostic factor.

CONCLUSIONS

Overexpression of pAkt is an independent prognostic factor. Additional studies of human NSCLCs are warranted to drive the development of targeted tumor-specific antineoplastic therapies.

Lung-specific expression of active Raf kinase results in increased mortality of influenza A virus-infected mice

Alterations in signalling via the Raf/MEK/ERK pathway interfere with influenza A virus replication in cell culture. While virus yields are reduced in cells expressing dominant-negative Raf or ERK, virus propagation is enhanced upon expression of constitutively active Raf or MEK. To study the impact of active Raf on influenza virus propagation in vivo, we investigated transgenic mice expressing an activated mutant of c-Raf (Raf-BxB) in the main target tissue of influenza virus, the lung. Raf-BxB expression results in multicentric alveolar adenomas. Influenza virus A infection of Raf-BxB mice results in increased disease symptoms and higher mortality rates. The immune response against viral pathogens in transgenic animals did not differ from wild-type mice as determined by the use of a Pseudorabies virus (PRV) as a model for a viral infection not affecting the lung. No significant differences of influenza virus titers in the lung of Raf-BxB and wild-type mice were observed. However, immunohistology revealed increased numbers of influenza NP-positive cells in the alveolar linings of Raf-BxB mice, demonstrating the strong tropism of influenza virus for cells expressing active Raf. These findings disclose the possibility to use modified influenza virus for the therapy of tumors with an activated Ras/Raf signalling pathway.

JAK/STAT, Raf/MEK/ERK, PI3K/Akt and BCR-ABL in cell cycle progression and leukemogenesis

The roles of the JAK/STAT, Raf/MEK/ERK and PI3K/Akt signal transduction pathways and the BCR-ABL oncoprotein in leukemogenesis and their importance in the regulation of cell cycle progression and apoptosis are discussed in this review. These pathways have evolved regulatory proteins, which serve to limit their proliferative and antiapoptotic effects. Small molecular weight cell membrane-permeable drugs that target these pathways have been developed for leukemia therapy. One such example is imatinib mesylate, which targets the BCR-ABL kinase as well as a few structurally related kinases. This drug has proven to be effective in the treatment of CML patients. However, leukemic cells have evolved mechanisms to become resistant to this drug. A means to combat drug resistance is to target other prominent signaling components involved in the pathway or to inhibit BCR-ABL by other mechanisms. Treatment of imatinib-resistant leukemia cells with drugs that target Ras (farnysyl transferase inhibitors) or with the protein destabilizer geldanamycin has proven to be a means to inhibit the growth of resistant cells. This review will tie together three important signal transduction pathways involved in the regulation of hematopoietic cell growth and indicate how their expression is dysregulated by the BCR-ABL oncoprotein.

Treatment with lovastatin, cholestyramine or niacin alters K-ras membrane association in mouse lung in a strain-dependent manner: results in females

Hypocholesterolemic drugs may themselves increase (cholestyramine, CS) or decrease (lovastatin, Lov) peripheral tissue de novo cholesterol biosynthesis. This will alter the abundance of prenyl groups and potentially increase (CS) or decrease (Lov) K-ras membrane localization, with possible pro- or anti-carcinogenic effects (K-ras is a proto-oncogene frequently mutated in lung cancer). Female A/J, Swiss, and C57BL/6 mice were fed 2 or 4% CS, 1% niacin, or injected with Lov three (Lov-3x) or five (Lov-5x) times per week. After three weeks, serum cholesterol and triglycerides were determined enzymatically. Total, membrane, and cytoplasmic K-ras proteins were determined in lung homogenates by immunoprecipitation followed by Western blotting with a K-ras specific antibody. CS feeding increased membrane K-ras as hypothesized in A/J and C57BL/6 mice, but had no effect in Swiss mice. Lov failed in all three strains to reduce membrane K-ras, and resulted in an increase in total K-ras in A/J and C57BL/6 mice, while again lacking effect in Swiss mice. Niacin had no effect on K-ras protein in any mouse strain. These results differ from our published results for male mice of the same strains, particularly for A/J mice. Increased amounts of K-ras protein in the membrane fraction of A/J females (but not males) treated with either Lov or CS imply that if K-ras were to become mutated, CS could result in increased lung tumorigenesis and Lov would be less likely to be protective in females. In the light of these data, both sexes should be included in future animal and human chemoprevention trials.

Responses of tumorigenic and non-tumorigenic mouse lung epithelial cell lines to electrophilic metabolites of the tumor promoter butylated hydroxytoluene

A model system to investigate the promotion phase of pulmonary carcinogenesis involves chronic exposure of carcinogen-initiated mice to the food additive, butylated hydroxytoluene (BHT). Previous studies strongly suggested that this activity is due to the cytochrome p450-catalyzed formation of quinone methides 2,6-di-tert-butyl-4-methylenecyclohexa-2,5-dienone (BHT-QM) and 6-tert-butyl-2-(1',1'-dimethyl-2'-hydroxy)ethyl-4-methylenecyclohexa-2,5-dienone (BHTOH-QM). The effects of these electrophiles on non-tumorigenic C10 and E10 epithelial cell lines derived from a normal mouse lung explant were compared with effects on their corresponding neoplastic siblings, the A5 and E9 spontaneous transformants, respectively. The tumorigenic cells were more resistant to cell killing, with LC(50) values of 165-180 microM for BHT-QM and 12-22 microM for BHTOH-QM, versus LC(50) values in the non-tumorigenic cells of 105-118 microM and 5.0-6.0 microM, respectively. Constitutive glutathione (GSH) concentrations were 12-20 nmol/10(6) cells, and BHT-QM toxicity was enhanced >2-fold by depleting GSH with buthionine sulfoximine (BSO). Formation of the GSH conjugate of BHT-QM accounted for a substantial fraction of the cellular GSH lost by quinone methide exposure. Enhanced lipid peroxidation and superoxide formation occurred in all cell lines treated with BHT-QM, but both tumorigenic lines contained higher levels of GSH S-transferase and superoxide dismutase (SOD) activities. These data suggest the possibility that BHT-derived quinone methides may exert their promoting effects by inducing oxidative stress; such stress is better tolerated by tumorigenic cells, which have higher levels of antioxidant enzymes. Normal cells are destroyed more readily which allows neoplastic cells to expand their proliferation.

Pharmacogenetics of anticancer drug sensitivity in non-small cell lung cancer

In mammalian cells, the process of malignant transformation is characterized by the loss or down-regulation of tumor-suppressor genes and/or the mutation or overexpression of proto-oncogenes, whose products promote dysregulated proliferation of cells and extend their life span. Deregulation in intracellular transduction pathways generates mitogenic signals that promote abnormal cell growth and the acquisition of an undifferentiated phenotype. Genetic abnormalities in cancer have been widely studied to identify those factors predictive of tumor progression, survival, and response to chemotherapeutic agents. Pharmacogenetics has been founded as a science to examine the genetic basis of interindividual variation in drug metabolism, drug targets, and transporters, which result in differences in the efficacy and safety of many therapeutic agents. The traditional pharmacogenetic approach relies on studying sequence variations in candidate genes suspected of affecting drug response. However, these studies have yielded contradictory results because of the small number of molecular determinants of drug response examined, and in several cases this approach was revealed to be reductionistic. This limitation is now being overcome by the use of novel techniques, i.e., high-density DNA and protein arrays, which allow genome- and proteome-wide tumor profiling. Pharmacogenomics represents the natural evolution of pharmacogenetics since it addresses, on a genome-wide basis, the effect of the sum of genetic variants on drug responses of individuals. Development of pharmacogenomics as a new field has accelerated the progress in drug discovery by the identification of novel therapeutic targets by expression profiling at the genomic or proteomic levels. In addition to this, pharmacogenetics and pharmacogenomics provide an important opportunity to select patients who may benefit from the administration of specific agents that best match the genetic profile of the disease, thus allowing maximum activity.

Cell condition-dependent regulation of ERK5 by cAMP

ERK5 activity is increased by agents known to activate receptor tyrosine kinases, G-protein coupled receptors, and stress response pathways. We now find a role for cAMP in the regulation of ERK5. ERK5 is activated by forskolin, isoproterenol, and epinephrine in NIH3T3 cells and C2C12 myoblasts. ERK1/2 are also activated by cAMP in NIH3T3 cells, but not in C2C12 myoblasts, demonstrating differential regulation of ERK5 and ERK1/2 by cAMP. We examined the effect of cell context on activation of ERK5 and discovered ERK5 activity is inhibited, rather than activated, by cAMP in confluent, serum-deprived NIH3T3 cells and C2C12 myoblasts. Our results suggest that regulation of MAP kinase pathways by cAMP is not only dictated by cell type, but also by cell context.

Alterations in membrane-bound and cytoplasmic K-ras protein levels in mouse lung induced by treatment with lovastatin, cholestyramine, or niacin: effects are highly mouse strain dependent

Agents that either increase (cholestyramine, CS) or decrease (lovastatin, Lov) de novo peripheral cholesterol synthesis may increase (CS) or decrease (Lov) ras protein membrane localization by altering protein prenylation, and potentially have pro- or anti-carcinogenic effects. Male A/J, Swiss, and C57/BL6 mice were treated with 2 or 4% CS, 1% dietary niacin, or 25mg/kg of Lov three times per week (Lov-3X) or five times per week (Lov-5X). After 3 weeks, serum cholesterol and triglycerides were determined enzymatically. Membrane and cytoplasmic K-ras proteins in lung were determined by immunoprecipitation followed by western blotting with a K-ras specific antibody. Results confirmed the hypothesis only in isolated instances. A/J mice had a significant 30% increase in cytoplasmic K-ras and a 40% decrease in membrane K-ras from Lov treatment, as predicted. C57/BL6 mice had a significant 77% increase in membrane K-ras, as expected from CS feeding. At variance with the hypothesis, Swiss mice had increased levels (3-28%) of membrane K-ras with all treatments (including Lov), and C57/BL6 mice treated with Lov had a 58-78% increase in cytoplasmic K-ras without any reduction in the levels of membrane K-ras. Niacin, predicted to have no effect on ras membrane localization, decreased cytoplasmic K-ras in A/J mice, increased both membrane and cytoplasmic K-ras in Swiss mice, and had no effect in C57/BL6 mice. Results may have differed from those predicted because of strain-dependent differences in response to the cholesterol-lowering agents. A difference in response among the mouse strains suggests that individual genetic differences may alter the effect of hypocholesterolemic agents on K-ras membrane localization, and potentially the risk of ras-dependent cancer.

The Role of Farnesyltransferase Inhibitors in Lung Cancer Therapy

Protein farnesylation is required for the localization and function of several proteins pivotal to signal transduction pathways and cytoskeletal organization, including the Ras proteins. Ras proteins are constitutively activated in 30% of human tumors, including lung cancer tumors, as a consequence of mutations in ras genes. Farnesyltransferase inhibitors (FTIs) were thus designed to curtail the Ras-mediated aberrant signals that regulate cell proliferation, apoptosis, invasion, and angiogenesis. These processes are vital to the perpetuation of the malignant phenotype. However, current evidence suggests that the antitumor activity of FTIs is Ras-independent. This article reviews preclinical and clinical data pertinent to the use of FTIs in lung cancer.

The intracellular mechanism of alpha-fetoprotein promoting the proliferation of NIH 3T3 cells

AIM

The existence and properties of alpha-fetoprotein (AFP) receptor on the surface of NIH 3T3 cells and the effects of AFP on cellular signal transduction pathway were investigated.

METHODS

The effect of AFP on the proliferation of NIH 3T3 cells was measured by incorporation of 3H-TdR. Receptor-binding assay of 125I-AFP was performed to detect the properties of AFP receptor in NIH 3T3 cells. The influences of AFP on the [cAMP]i and the activities of protein kinase A (PKA) were determined. Western blot was used to detect the change of K-ras P21 protein expression.

RESULTS

The proliferation of NIH 3T3 cells treated with 0-80 mg/L of AFP was significantly enhanced. The Scatchard analysis indicated that there were two classes of binding sites with KD of 2.722 x 10(-9)M (Bmax=12810 sites per cell) and 8.931 x 10(-8)M (Bmax=119700 sites per cell) respectively. In the presence of AFP (20 mg/L), the content of cAMP and activities of PKA were significantly elevated . The level of K-ras P21 protein was upregulated by AFP at the concentration of 20 mg/L. The monoclonal antibody against AFP could reverse the effects of AFP on the cAMP content, PKA activity and the expression of K-ras p21 gene.

CONCLUSION

The effect of AFP on the cell proliferation was achieved by binding its receptor to trigger the signal transduction pathway of cAMP-PKA and alter the expression of K- ras p21 gene.

Decrease in K-ras p21 and increase in Raf1 and activated Erk 1 and 2 in murine lung tumors initiated by N-nitrosodimethylamine and promoted by 2,3,7,8-tetrachlorodibenzo-p-dioxin

Recent evidence suggests that K-ras protooncogene protein p21 may have a tumor-suppressive role in the context of development of lung adenocarcinoma. Levels of K-ras p21, raf-1, mitogen-activated protein kinases Erk 1 and 2, the phosphorylated-activated forms of Erk 1 and 2 (Erk 1P and 2P), and proliferating cell nuclear antigen (PCNA) were measured by immunoblotting in mouse lung tumors (5 to 9 mm in size) caused by N-nitrosodimethylamine (NDMA) and in control lungs. In tumors compared with normal lung, cell membrane-associated K-ras p21 was significantly decreased and cytosolic K-ras p21 increased. Total, membrane, and cytosolic raf-1 and Erk 1P and 2P were increased in tumors compared with normal lung. A single dose of 5 nmol/kg 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) given after NDMA resulted in a significant 2.4-fold increase in tumor multiplicity. A significantly greater decrease in membrane-associated K-ras p21 and increase in total and membrane associated raf-1 occurred in the NDMA/TCDD tumors compared with the NDMA-only tumors. PCNA levels increased in tumors, a finding confirmed by immunohistochemistry, and correlated with tumor size after NDMA/TCDD treatment but not after NDMA only. The increase in raf-1 in the tumors was confirmed by immunohistochemistry, which also revealed an increase in raf-1-positive alveolar macrophages specifically associating with tumors from the earliest stages. These results suggest a possible tumor-suppressive function for K-ras p21 in lung and a positive role for raf-1 and Erk 1/2 in lung tumorigenesis. TCDD may promote tumors by contributing to downregulation of K-ras and stimulation of raf-1.