Midkine induces the transformation of NIH3T3 cells.

Midkine (MK) is a heparin-binding growth factor and is frequently expressed at high levels in many human carcinomas. To investigate further the roles of MK in the regulation of cell growth, we introduced MK expression in NIH3T3 cells. A mixture of transfectants of an MK expression vector, but not a control vector, formed colonies in soft agar, showed an elevated cell number at confluence, and formed tumours in nude mice. An interesting characteristic of the transformed cells was that they became spontaneously detached from the culture dish substratum. In the transformed cells, MK was not only secreted, but also localized, in the perinuclear region as spots. The present data indicate that MK has the potential to transform NIH3T3 cells and suggest that overexpression of the MK gene may promote unregulated cell growth in vivo.     

Isoforms of c-KIT differ in activation of signalling pathways and transformation of NIH3T3 fibroblasts.

Alternate splicing of mRNA encoding c-KIT results in isoforms which differ in the presence or absence of four amino acids (GNNK) in the juxtamembrane region of the extracellular domain of the receptor. In this study we show that these isoforms of human c-KIT, expressed at similar levels in NIH3T3 cells, display differential effects on various attributes of transformation. The GNNK- isoform strongly promoted anchorage independent growth (colony formation in semi-solid medium), loss of contact inhibition (focus formation), and led to tumorigenicity in nude mice. In contrast, the GNNK+ isoform elicited colony formation but relatively poor focus formation and no tumorigenicity. Saturation binding analysis indicated that the isoforms do not differ significantly in their affinity for the KIT ligand, Steel Factor (SLF). Negligible ligand-independent receptor phosphorylation was observed in either case but, after ligand stimulation, the GNNK- isoform displayed more rapid and extensive tyrosine autophosphorylation and faster internalization. Both isoforms recruited the p85 subunit of phosphatidylinositol 3-kinase and led to similar phosphorylation of its downstream effector c-Akt, but the GNNK- isoform gave rise to more MAP kinase phosphorylation. Thus the c-KIT isoforms display different signalling characteristics and have different transforming activity in NIH3T3 cells.     

Malignant transformation of NIH 3T3 fibroblasts by human c-sis is dependent upon the level of oncogene expression.

High-level expression of the c-sis oncogene, which encodes the beta chain of platelet-derived growth factor, transforms immortalized rodent fibroblasts in vitro to a malignant phenotype. c-sis gene expression has been demonstrated in a variety of human tumors, although generally at levels much lower than those shown to transform cells in vitro. We examined the effect of lower levels of c-sis expression on the phenotype of NIH 3T3 fibroblasts. Clones with various levels of c-sis expression were generated by transfecting NIH 3T3 cells with a plasmid that expressed the human c-sis cDNA and the TN5 neomycin-resistance gene. G418-resistant clones, which expressed the c-sis cDNA, were selected and characterized. Alterations in the phenotype of the clones that expressed c-sis ranged from increased growth in soft agar to malignant tumor formation in nude and syngeneic mice. Increased levels of c-sis cDNA expression correlated with the acquisition of features of transformation in a dose-dependent manner and altered the cellular phenotype in a manner consistent with the progression of cells towards malignancy. These data support a model in which low levels of sis gene expression in tumors contribute to the acquisition of some features of transformation but require complementation by other genes or factors to produce a fully malignant phenotype.     

Selective activation of oncogenic Ha-ras-induced apoptosis in NIH/3T3 cells.

A Ha-ras transformant ''7-4'', derived from mouse NIH/3T3 fibroblasts, was used to study the relationship between overexpression of activated Ha-ras and cell apoptosis. This cell line contains an inducible Ha-rasVal12 oncogene, which was under the regulation of the Escherichia coli (E. coli) lac operator/repressor system. We demonstrate that overexpression of activated Ha-ras oncogene by exogenous isopropyl-beta-D-thiogalactoside (IPTG) under serum-depleted conditions can stimulate cell apoptosis. Cell cycle analysis showed that most of the 7-4 cells with Ha-ras overexpression accumulated at S-phase and that the expression level of p34cdc2 kinase was decreased, suggesting that p34cdc2 may be involved in 7-4 cell apoptosis. Overexpression of bcl-2 transgene in these cells blocked Ha-ras-induced apoptosis, and this blockage was confirmed downstream of Ha-ras gene expression. Cycloheximide blocked the apoptosis of 7-4 cells in a dose-dependent manner, indicating that specific protein regulating apoptosis may be synthesized through Ha-ras overexpression. Ha-ras overexpression-triggered apoptosis was also prevented in the 7-4 derivatives that express either dominant-negative rasAsn17 or dominant-negative raf-1C4B to suppress Ha-ras signal transduction at different stages, indicating that overexpression of activated Ha-ras can induce cell apoptosis and that raf-1 pathway activity is required for this process.     

Calcium-induced activation of a mutant G-protein-coupled receptor causes in vitro transformation of NIH/3T3 cells

The calcium-sensing receptor (CaR) is a G-protein-coupled receptor that is widely expressed, has tissue-specific functions, and regulates cell growth. Activating mutations of this receptor cause autosomal dominant hypocalcemia, a syndrome characterized by hypocalcemia and hypercalciuria. The identification of a family with an activating mutation of the CaR (Thr151Met) in which hypocalcemia cosegregates with several unusual neoplasms led us to examine the transforming effects of this mutant receptor. Transfection of NIH/3T3 cells with the mutant but not the normal receptor supported colony formation in soft agar at subphysiologic calcium concentrations. The mutant CaR causes a calcium-dependent activation of the extracellular signal-regulated protein kinase (ERK) 1/2 and Jun-N-terminal kinase/stress-activated (JNK/SAPK) pathways, but not P38 MAP kinase. These findings contribute to a growing body of information suggesting that this receptor plays a role in the regulation of cellular proliferation, and that aberrant activation of the mutant receptor in this family may play a role in the unusual neoplastic manifestations.     

Inhibition of H-ras oncogene transformation of NIH3T3 cells by protease inhibitors

The protease inhibitors antipain, leupeptin, alpha 1-antitrypsin, and epsilon-aminocaproic acid were found to inhibit transformation of NIH3T3 cells after transfection with an activated H-ras oncogene. Inhibition of focus formation by protease inhibitors was concentration dependent and maximal at 50% of control values. Transfection of a gene for neomycin resistance was not affected by protease inhibitors. Antipain was inactive if present only during the first 2 days of the gene transfer protocol or only during the final 10 days of the experiment. However, the full effect was observed when antipain was added at the subculture step on day 3 and during the subsequent cell proliferation. If cells were not subcultured, the yield of the foci per microgram of DNA was sharply reduced and addition of antipain did not further suppress the transformation rate. Subculture of NIH3T3 cells 3 days after transfection at lower cell densities resulted in higher transformation efficiency. The results suggest that transformation of NIH3T3 cells by a single mutated oncogene may involve multiple stages including cell proliferation and that part of this process is susceptible to inhibition by protease inhibitors.     

Rho kinase regulates the survival and transformation of cells bearing oncogenic forms of KIT, FLT3, and BCR-ABL

We show constitutive activation of Rho kinase (ROCK) in cells bearing oncogenic forms of KIT, FLT3, and BCR-ABL, which is dependent on PI3K and Rho GTPase. Genetic or pharmacologic inhibition of ROCK in oncogene-bearing cells impaired their growth as well as the growth of acute myeloid leukemia patient-derived blasts and prolonged the life span of mice bearing myeloproliferative disease. Downstream from ROCK, rapid dephosphorylation or loss of expression of myosin light chain resulted in enhanced apoptosis, reduced growth, and loss of actin polymerization in oncogene-bearing cells leading to significantly prolonged life span of leukemic mice. In summary we describe a pathway involving PI3K/Rho/ROCK/MLC that may contribute to myeloproliferative disease and/or acute myeloid leukemia in humans.     

RACK1 regulates Ki-Ras-mediated signaling and morphological transformation of NIH 3T3 cells

Activating Ras mutations are involved in a significant fraction of human tumors. A suppressor screen using a retroviral mouse fibroblast cDNA library was performed to identify novel factors in Ras-mediated transformation. We identified a novel potent inhibitor of Ras-mediated morphological transformation encoded by a truncated version of the receptor for activated C-kinase (RACK1). The truncated protein, designated RACK1DeltaWD1, lacked the N-terminal 49 amino acids encoding the first of the 7 WD40 repeats in RACK1. RACK1DeltaWD1 expression restored contact inhibition, stress fiber formation and reduced ERK phosphorylation in Ki-Ras transformed NIH 3T3 cells. We demonstrate that truncated RACK1 is involved in complexes consisting of wild-type RACK1 and protein kinase C isoforms alpha, betaI and delta, compromising the transduction of an activated Ras signal to the Raf-MEK-ERK pathway. The cellular localization of RACK1DeltaWD1 differed from wtRACK1, indicating that signaling complexes containing the truncated version of RACK1 are incorrectly localized. Notably, 12-O-tetradecanoyl-13-phorbol acetate (TPA) mediated intracellular translocation of RACK1-interacting PKC alpha and delta was abrogated in RACK1DeltaWD1-expressing cells. Our data support a model where RACK1 acts as a key factor in Ki-Ras-mediated morphological transformation.     

Effect of adeno-associated virus on transformation of NIH 3T3 cells by ras gene and on tumorigenicity of an NIH 3T3 transformed cell line

Transfection of NIH-3T3 cells with the plasmid pJ234, containing DNA from the human bladder carcinoma T24 cell line (ras gene), results in their transformation. Adeno-associated virus did not affect significantly the number of the transformed foci when different multiplicities of infection were used and when the virus was added to the cultures at different time intervals before or after transfection. A transformed cell line was derived following transfection of NIH 3T3 cells by the ras gene. Infection of these cells with adeno-associated virus resulted in a decrease in their growth rate and cloning efficiency. These infected cells showed a dose-dependent reduction in the frequency and an increase in the latent period for tumor appearance in nude mice.     

Sensitivity pattern of normal and Ha-ras transformed NIH3T3 fibroblasts to antineoplastic drugs

Ha-ras-transformed NIH3T3 fibroblasts were compared with the parental cell line to investigate the influence of the Ha-ras oncogene on cellular chemosensitivity to antineoplastic drugs. Four NIH3T3 cell clones independently transformed by the Ha-ras oncogene, activated by mutation or overexpression, were analyzed: 3 clones were obtained by transfection of NIH3T3 cells with a mutation-activated Ha-ras gene and 1 clone by transfection of a large copy number of the normal Ha-ras proto-oncogene. Chemosensitivity of the transformed clones and of the parental cell line was analyzed when cells were in the same condition of proliferative activity and cell cycle phase distribution. No significant differences in chemosensitivity were observed between transformed and untransformed cell lines to doxorubicin, VP-16, cis-platinum or mitomycin C. Therefore, data suggest that activated Ha-ras oncogenes have no role in sensitivity to these antineoplastic agents.     

Overexpression of phosphoinositide-specific phospholipase Cgamma in NIH 3T3 cells promotes transformation and tumorigenicity

Phosphoinositide-specific phospholipase Cgamma (PLCgamma) is a key regulatory enzyme that binds to the phosphoryl-tyrosine residues in the cytoplasmic domain of certain activated receptors and catalyses the hydrolysis of phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2] forming IP3 and diacylglycerol (DAG) in response to several mitogenic factors. Previously, we determined that microinjected PLCgamma induces DNA synthesis in G0-arrested NIH 3T3 cells, suggesting the possibility that PLCgamma may have an oncogenic potential. In this report, we demonstrate that overexpression of PLCgamma in NIH 3T3 cells results in altered growth properties and cellular transformation. The PLCgamma/3T3 transfectants do not require serum growth factors to proliferate, display anchorage-independent growth in soft agar and induce tumors when transplanted into nude mice. These findings suggest that overexpression of PLCgamma facilitates the transformation of NIH 3T3 cells. Furthermore, PLCgamma expression and activity have been shown to be elevated in many human tumors. Thus, PLCgamma signaling may contribute to the promotion and/or progression of human cancers.      

Transformation of NIH3T3 fibroblasts by an expression vector for the human epidermal growth factor precursor

Epidermal growth factor (EGF) and transforming growth factor alpha (TGF alpha) bind to a common cell surface receptor that mediates their diverse biological activities. NIH3T3 fibroblasts transfected with either full-length EGF precursor (preproEGF) or proTGF alpha cDNA displayed distinct patterns of growth in culture. PreproEGF induced focal transformation, and transfectants grew in a chemically defined medium (CDM) at low cell density in the absence of added EGF. In contrast, TGF alpha failed to cause focal transformation, and transfectants grew in CDM in the absence of added growth factors only when seeded at high cell density. The 53 amino acid EGF portion of the preproEGF translation product was essential for its effects. These results indicate that constitutive expression of preproEGF is sufficient to establish autocrine growth of NIH3T3 expressing low levels of EGF receptors. At high cell density, where paracrine as well as autocrine effects of these growth factors would be evident, TGF alpha transfectants displayed at least as high or higher levels of EGF receptor (EGFR) tyrosine phosphorylation than preproEGF transfectants. Since quantitative levels of ligand expression did not account for differences in their transforming properties, preproEGF must be more efficient than proTGF alpha in binding and/or activating EGF receptors in an autocrine manner.     

Polyamine metabolism and interconversion in NIH 3T3 and ras-transfected NIH 3T3 cells

The effect of transfection of NIH 3T3 cells by the human ras (c-Ha-ras-1) oncogene on uptake, interconversion, and excretion of polyamines was studied. Uptake and interconversion of spermidine were higher in the ras-transfected cells. Acetylpolyamines were excreted into the medium by the ras-transfected cells, whereas they were retained by NIH 3T3 cells. In addition to acetylpolyamines, some unknown polyamine conjugates occurred in the ras-transfected cells.     

热休克蛋白90通过抑制Bid裂解抑制NIH3T3成纤维细胞凋亡

目的探讨热休克蛋白90(heatshockproteins90,HSP90)抑制肿瘤坏死因子α(tumornecrosisfactorα,TNFα)和放线菌酮(cycloheximide,CHX)诱导的细胞凋亡作用机制。方法采用电穿孔技术建立稳定过表达HSP90的细胞克隆;应用激光共聚焦显微镜和流式细胞仪,观察TNFα/CHX诱导的细胞凋亡及HSP90对细胞凋亡的拮抗作用;应用Westernblotting及免疫沉淀方法,检测HSP90是否直接作用于Bid(BH3interactingdeathag-onist)及HSP90抑制剂格尔德霉素的功能。结果在稳定过表达HSP90的NIH3T3细胞中,HSP90能够抑制TNF-α/CHX诱导的细胞凋亡;HSP90通过直接与Bid结合阻止Bid的裂解来抑制TNF-α/CHX诱导的细胞凋亡;HSP90的特异性抑制剂格尔德霉素可以拮抗HSP90,阻止Bid裂解。结论HSP90的大量存在(即使在生理条件下)不仅通过促进蛋白质的折叠,而且通过阻止Bid的裂解而保持前凋亡因子的惰性状态,使细胞免于凋亡,对细胞稳态的维持发挥重要作用;HSP90抑制剂作为抗肿瘤药物的一个作用机制,可能通过促进Bid从HSP90复合物中释放,进而促进肿瘤细胞凋亡。     

Overexpression of antizyme-inhibitor in NIH3T3 fibroblasts provides growth advantage through neutralization of antizyme functions

Antizyme inhibitor (AzI) is a homolog of ornithine decarboxylase (ODC), a key enzyme of polyamine synthesis. Antizyme inhibitor retains no enzymatic activity, but exhibits high affinity to antizyme (Az), a negative regulator of polyamine homeostasis. As polyamines are involved in maintaining cellular proliferation, and since AzI may negate Az functions, we have investigated the role of AzI in regulating cell growth. We show here that overexpression of AzI in NIH3T3 cells increased growth rate, enabled growth in low serum, and permitted anchorage-independent growth in soft agar, while reduction of AzI levels by AzI siRNA reduced cellular proliferation. Moreover, AzI overproducing cells gave rise to tumors when injected into nude mice. AzI overexpression resulted in elevation of ODC activity and of polyamine uptake. These effects of AzI are a result of its ability to neutralize Az, as overexpression of an AzI mutant with reduced Az binding failed to alter cellular polyamine metabolism and growth properties. We also demonstrate upregulation of AzI in Ras transformed cells, suggesting its relevance to some naturally occurring transformations. Finally, increased uptake activity rendered AzI overproducing and Ras-transformed cells more sensitive to toxic polyamine analogs. Our results therefore imply that AzI has a central and meaningful role in modulation of polyamine homeostasis, and in regulating cellular proliferation and transformation properties.     

Expression of full length or truncated epidermal growth factor precursor transforms NIH3T3 fibroblasts.

Epidermal growth factor (EGF) is derived from a large precursor (EGFP) of unusual structure. As EGFP remains unprocessed in certain tissues, it is of biological relevance to study its activity. Activation of the EGF receptor by EGF is involved in transformation of NIH3T3 fibroblasts. We isolated clones of NIH3T3 expressing full length, cytoplasmic region deleted or EGF-repeats deleted EGFP. All clones formed colonies in soft agarose and tumors in nude mice. Two clones expressing EGF-repeats deleted EGFP formed more and larger colonies. To conclude, EGFP is biologically active. Deletion of the 8 EGF repeats may enhance anchorage independent growth in NIH3T3.     

Antigens expressed on NIH 3T3 cells following transformation with DNA from human pancreatic tumor

This report documents that the pancreatic adenocarcinoma cell line, HPAF, contains oncogene activity detected by transformation of NIH 3T3 cells through transfection with HPAF DNA. The HPAF transfected NIH 3T3 cells do not contain oncogenes homologous with c-H-ras, c-K-ras, c-N-ras, v-fms, c-myb, c-sis, v-fgr, c-mos, c-myc, c-fos, v-fes, v-src, v-erb A, v-erb B, c-N-myc, v-raf, or v-abl, other than the endogenous mouse genes. The transfectants do express proteins detected by two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis which were not found in nontransfected NIH 3T3 cells. Monoclonal antibodies raised against the transfectants recognize proteins not found in untransfected NIH 3T3 cells that are antigenically identical to proteins found in the HPAF cells. These antigens are also detected on six other human pancreatic adenocarcinoma cell lines but show a much more restricted distribution on lymphoblastoid, melanoma, prostatic carcinoma, and normal skin fibroblast cell lines.     

林县人尿中的亚硝基异脯氨酸对NIH3T3细胞的恶性转化作用

N-Nitrosothiazolidine 4-carboxylic acid (NTCA), a nonvolatile N-Nitroso compound containing sulfur was first found in the urine of normal subjects in Lin-xian county, a high risk area of esophageal cancer. The content of NTCA in the urine of the general population of Lin-xian is higher than that in Fan-xian county, a low risk area of esophageal cancer. NTCA could induce mutation in V79 cells. The results showed that NIH 3T3 cells could be induced to undergo malignant transformation by NTCA. If NIH 3T3 cells were cultured in soft agar medium, transformed cells could grow progressively to form colonies and became anchorage-independent. These transformed cells were tumorigenic in nude mice. The above results indicate that NTCA formed in vivo, being one of the risk factors of esophageal cancer in Lin-xian county, is a potential carcinogen. This investigation also demonstrates that the N-Nitroso compounds are closely related to esophageal cancer.