Immortalization by c-myc, H-ras, and Ela oncogenes induces differential cellular gene expression and growth factor responses.

Abstract

Early-passage rat kidney cells were immortalized or rescued from senescence with three different oncogenes: viral promoter-driven c-myc, H-ras (Val-12), and adenovirus type 5 E1a. The normal c-myc and H-ras (Gly-12) were unable to immortalize cells under similar conditions. Quantitation of RNA in the ras-immortalized lines demonstrated that the H-ras oncogene was expressed at a level equivalent to that of the normal H-ras gene in established human or rat cell lines. Cell lines immortalized by different oncogenes were found to have distinct growth responses to individual growth factors in a short-term assay. E1a-immortalized cells were largely independent of serum growth factors, whereas c-myc-immortalized cells responded to serum better than to epidermal growth factor and insulin. H-ras-immortalized cells responded significantly to insulin alone and gave a maximal response to epidermal growth factor and insulin. Several cellular genes associated with platelet-derived growth factor stimulation, including c-myc, were expressed at high levels in the H-ras-immortalized cells, and c-myc expression was deregulated, suggesting that the H-ras oncogene has provided a "competence" function. H-ras-immortalized cells could not be morphologically transformed by secondary transfection with a long terminal repeat-c-myc oncogene, but secondary transfection of the same cells with H-ras (Val-12) produced morphologically transformed colonies that had 20- to 40-fold higher levels of H-ras oncogene expression. Thus, transformation in this system is dependent on high levels of H-ras oncogene expression rather than on the presence of activated H-ras and c-myc oncogenes in the same cell.

Adenovirus 5 E1A is responsible for increased expression of insulin receptor substrate 4 in established adenovirus 5-transformed cell lines and interacts with IRS components activating the PI3 kinase/Akt signalling pathway

“…The Ad5E1A13S-mediated increase in IRS-4 expression may explain earlier observations of the growth factor requirements of AdE1-transformed cells, that is, the proliferation of Ad5E1-transformed cells is relatively unaffected by removal of extrinsic growth factors, such as insulin and IGF-1, whereas Ad12E1-transformed cells show a marked decrease in their proliferation (Kelekar and Cole, 1987;Timmers et al, 1988). Our results indicate that this is because of increased expression of IRS-4 in Ad5E1A13S expressing cells, which is able to associate with PI3 kinase and activate Akt, even in serum-starved conditions (Figures 7a-c).…”

Telomerase reverse transcriptase mediated immortalization of human bone marrow stromal cells

“…MSCs are also known as marrow stromal stem cells and marrow mesenchymal stem cells (Richardson et al 2010;Zellner et al 2010 (Satija et al 2007). In several studies, exogenous virus, or oncogene has been introduced to target the cells to construct the immortalized cells (Kelekar and Cole 1987;Arimura et al 2007;Wu et al 2007), in which the integration of target gene was random and expression of target gene might have interfered with the intracellular physiological processes, which could result in unexpected changes such as loss of differentiation characteristic and lack of control of check point. The cells treated with virus, or oncogene belong to transformed cells but not the normal cells, and thus they are different partially, or completely from the normal cells in the transformation features such as changes in cell morphology, karyotype and tumorigenicity, as well as loss of suspended growth and contact inhibition (Gipson et al 2007).…”

Overexpression of an Activated rasG Gene during Growth Blocks the Initiation of Dictyostelium Development

“…For example, transfection of rat Schwann cells with activated Haras prevents outgrowth of these cells, and microinjection of oncogenic Ras proteins into these cells inhibits DNA synthesis (34). Furthermore, in cultured rat kidney cells, only low levels of activated ras expression are tolerated (20), and overexpression of an activated Ha-Ras protein in REF52 rat embryo fibroblast cells induces morphological changes and cell growth arrest (14). Finally, in PC12 cells, an activated ras gene induces cell growth arrest and neurite differentiation (2,36).…”