Neoplastic transformation of a human kidney epithelial cell line transfected with v-Ha-ras oncogene

Evaluation of renal in vitro models used in ochratoxin research

Ochratoxin A (OTA) induces renal carcinomas in rodents with a specific localisation in the S3 segment of proximal tubules and distinct early severe tissue alterations, which have been observed also in other species. Pronounced species- and sex-specific differences in toxicity occur and similar effects cannot be excluded in humans, however precise mechanism(s) remain elusive until today. In such cases, the use of in vitro models for mechanistic investigations can be very useful; in particular if a non-genotoxic mechanism of cancer formation is assumed which include cytotoxic effects. However, potential genotoxic mechanisms can also be investigated in vitro. A crucial issue of in vitro research is the choice of the appropriate cell model. Apparently, the cellular target of OTA is the renal proximal tubular cell; therefore cells from this tissue area are the most reasonable model. Furthermore, cells from affected species should be used and can be compared to cells of human origin. Another important parameter is whether to use primary cultures or to choose a cell line from the huge variety of cell lines available. In any case, important characteristics and quality controls need to be verified beforehand. Therefore, this review discusses the renal in vitro models that have been used for the investigation of renal ochratoxin toxicity. In particular, we discuss the choice of the models and the essential parameters making them suitable models for ochratoxin research together with exemplary results from this research. Furthermore, new promising models such as hTERT-immortalised cells and 3D-cultures are briefly discussed.

H-ras-transformed NRK-52E renal epithelial cells have altered growth, morphology, and cytoskeletal structure that correlates with renal cell carcinoma in vivo

We studied the effect of the ras oncogene on the growth kinetics, morphology, cytoskeletal structure, and tumorigenicity of the widely used NRK-52E rat kidney epithelial cell line and two H-ras oncogene-transformed cell lines, H/1.2-NRK-52E (H/1.2) and H/6.1-NRK-52E (H/6.1). Population doubling times of NRK-52E, H/1.2, and H/6.1 cells were 28, 26, and 24 h, respectively, with the transformed cells reaching higher saturation densities than the parent cells. NRK-52E cells had typical epithelial morphology with growth in colonies. H/1.2 and H/6.1 cell colonies were more closely packed, highly condensed, and had increased plasma membrane ruffling compared to parent cell colonies. NRK-52E cells showed microfilament, microtubule, and intermediate filament networks typical of epithelial cells, while H/1.2 and H/6.1 cells showed altered cytoskeleton architecture, with decreased stress fibers and increased microtubule and intermediate filament staining at the microtubule organizing center. H/1.2 and H/6.1 cells proliferated in an in vitro soft agar transformation assay, indicating anchorage-independence, and rapidly formed tumors in vivo with characteristics of renal cell carcinoma, including mixed populations of sarcomatoid, granular, and clear cells. H/6.1 cells consistently showed more extensive alterations of growth kinetics, morphology, and cytoskeleton than H/1.2 cells, and formed tumors of a more aggressive phenotype. These data suggest that analysis of renal cell characteristics in vitro may have potential in predicting tumor behavior in vivo, and significantly contribute to the utility of these cell lines as in vitro models for examining renal epithelial cell biology and the role of the ras proto-oncogene in signal transduction involving the cytoskeleton.

Differential effect of polyunsaturated fatty acids on cell proliferation during human epithelial in vitro carcinogenesis: involvement of epidermal growth factor receptor tyrosine kinase

Polyunsaturated fatty acids (PUFAs) have been implicated in tumour development and have been shown to influence cell proliferation in vitro. We report here that n-3 and n-6 PUFAs at concentration > 10 microM inhibited the proliferation of a human kidney epithelial cell line (21HKE), which has retained phenotypic characteristics of normal kidney epithelial cells. In contrast, the proliferation was stimulated by n-3 and n-6 PUFAs at concentrations < 10 microM under defined growth conditions. The stimulatory effect of n-3 and n-6 PUFAs was even more profound in the presence of EGF. In human kidney epithelial cell lines reflecting different stages of transformation (11HKE and 1THKEras), the stimulatory effect was abrogated both in the presence and absence of EGF. Saturated fatty acids did not show any stimulatory effect on cell growth. The tyrosine kinase inhibitors genistein and tyrphostin-47 inhibited EGF-induced protein tyrosine phosphorylation dose-dependently in the 21HKE cells, and abolished the growth stimulatory effect of docosahexaenoic acid (DHA). This indicates the involvement of EGF receptor tyrosine kinase activity in the observed increase in cell proliferation.

Host range restrictions of oncogenes: myc genes transform avian but not mammalian cells and mht/raf genes transform mammalian but not avian cells

The host range of retroviral oncogenes is naturally limited by the host range of the retroviral vector. The question of whether the transforming host range of retroviral oncogenes is also restricted by the host species has not been directly addressed. Here we have tested in avian and murine host species the transforming host range of two retroviral onc genes, myc of avian carcinoma viruses MH2 and MC29 and mht/raf of avian carcinoma virus MH2 and murine sarcoma virus MSV 3611. Virus vector-mediated host restriction was bypassed by recombining viral oncogenes with retroviral vectors that can readily infect the host to be tested. It was found that, despite high expression, transforming function of retroviral myc genes is restricted to avian cells, and that of retroviral mht/raf genes is restricted to murine cells. Since retroviral oncogenes encode the same proteins as certain cellular genes, termed protooncogenes, our data must also be relevant to the oncogene hypothesis of cancer. According to this hypothesis, cancer is caused by mutation of protooncogenes. Because protooncogenes are conserved in evolution and are presumed to have conserved functions, the oncogene hypothesis assumes no host range restriction of transforming function. For example, mutated human proto-myc is postulated to cause Burkitt lymphoma, because avian retroviruses with myc genes cause cancer in birds. But there is no evidence that known mutated protooncogenes can transform human cells. The findings reported here indicate that host range restriction appears to be one of the reasons (in addition to insufficient transcriptional activation) why known, mutated protooncogenes lack transforming function in human cells.

Proliferative heterogeneity of human renal cell carcinomas and prevalence of ras gene point mutations

The variable prevalence and a possible stage-dependent increase of ras gene point mutations in human tumors might correspond to clonal growth advantages of ras-activated cells. Tumor areas with activated ras genes might thus differ in proliferative activity from those lacking ras gene activation. This hypothesis is studied in a series of human renal cell carcinomas that had been used previously for an analysis of proliferative compartments after post-operative vascular [3H]/[14C]thymidine perfusion [Rabes et al. (1979) Cancer 44: 799-813]. The growth fraction of different subcompartments of these tumors was studied by immunohistochemistry with mib1 antibody, recognizing a fixation- and embedding-resistant epitope of Ki-67 protein. Thirty subpopulations of 14 human renal cell carcinomas that exhibited a broad spectrum of proliferative activity were chosen for an analysis of the prevalence of K-ras point mutations in exon 1 by a mutation-enriching primer-mediated restriction-fragment-length-polymorphism analysis and/or direct sequencing of polymerase-chain-reaction-amplified material. The combined autoradiographic and immunohistochemical analysis confirmed the intra- and intertumoral proliferative heterogeneity. Compared to [3H]/[14C]thymidine labeling indices, mib1 labeling indices are higher. The ratio of mib1 to [3H]/[14C]thymidine labeling indices varies from 1.9 to 4.1 for the individual tumor subcompartments. However, neither in K-ras codons 12/13 nor in adjacent codons did we detect any mutations in the various tumor compartments. The results suggest that neither mode of proliferation nor type of differentiation is related to K-ras exon 1 point mutations in human renal cell carcinomas.

Direct tumorigenic conversion of human gallbladder carcinoma cells by v-src but not by activated c-H-ras oncogene

The roles of activated ras and src oncogene products in the acquisition of fully neoplastic phenotype by human gallbladder adenocarcinoma cells were investigated by co-transfecting non-tumorigenic HAG-I human gallbladder carcinoma cells with the pSV2neo plasmid and a plasmid carrying either activated c-H-ras or v-src oncogene. G418-resistant clones were isolated and assessed for the acquisition of anchorage-independent growth potential. Neither the 10 established clones transfected with pSV2neo alone nor the 17 clones transfected with activated c-H-ras, including 4 clones expressing the mutated p21H-ras protein, could form colonies in soft agar. By contrast, out of 10 clones transfected with v-src, 2 formed colonies in soft agar and produced tumors in athymic nude mice, the resulting progressive neoplasms being poorly differentiated adenocarcinomas. These tumorigenic clones were shown to have v-src DNA and mRNA levels with p60v-src protein, but there were no significant chromosomal alterations following tumorigenic conversion. Moreover, herbimycin A, a selective src-kinase inhibitor, markedly reduced clonogenic growth of these cells in soft agar rather than monolayer growth, suggesting that anchorage-independent growth of the v-src-transformed HAG-I cells might be driven directly by p60v-src kinase activity. Taken together, our data suggest that the fully neoplastic conversion of HAG-I cells depends on src-related tyrosine-kinase activity, but not solely on the function mediated by activated ras, thus providing evidence of an src-related signaling pathway for the acquisition of tumorigenic potential by human gallbladder adenocarcinoma cells.

Effects of n-3 fatty acids during neoplastic progression and comparison of in vitro and in vivo sensitivity of two human tumour cell lines

Several studies have shown that dietary lipid exerts an effect on carcinogenesis. We report here that progression to malignancy in vitro is associated with changes in the response to fatty acids (FAs). Tumorigenic (THKE) cells were more sensitive to the n-3 FAs eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) than immortalised (IHKE) cells. The growth of THKE cells was inhibited 25% more than the growth of IHKE cells at 80 microM EPA (P < 0.01) and 35% more at 40 microM DHA (P < 0.001). Furthermore, the results indicate that there is a wide cell type variation in the response to FAs. We found that the in vitro inhibition by FAs correlated with the reduction in the growth rate of the tumour in nude mice fed K85 (55% EPA and 30% DHA). A significant difference in tumour latency was observed for the A427 cell tumour groups (10 days, P < 0.05). Tumours in the animals fed n-3 FA exhibited significantly higher levels of EPA and DHA; the level of arachidonic acid (ARA) was significantly lower in THKE tumours and the level of linoleic acid (LA) was significantly lower in A427 tumours than in controls fed corn oil. The higher sensitivity of the A427 cell line was not explained by higher uptake of EPA/DHA.

Mutations in the ras protooncogenes are rare events in renal cell cancer

Mutations in codon 12, 13 or 61 of one of the three ras genes, Ha-ras, Ki-ras, and N-ras, convert these genes into active oncogenes. To determine the role mutated ras genes play in the carcinogenesis of renal cell carcinoma, we analysed tumour DNA and unaffected renal tissue derived from 55 patients. The polymerase chain reaction technique was used to amplify DNA fragments containing Ki-, Ha-, and N-ras codons 12, 13, and 61. The amplified fragments were then probed on slot-blots with labeled mutation-specific oligomers. A single Ki-ras mutation (codon 12, gly- greater than val) was detected in a patient with a pT2N2M1 tumour. We concluded that ras oncogene mutations do not play an important role in the initiation of renal cell carcinoma.