Immortalization of human embryonic fibroblasts by overexpression of c-myc and simian virus 40 large T antigen

Abstract

SV40 large T antigen, a viral oncoprotein, is known to immortalize human diploid fibroblast by soaking up cellular RB and p53, but its frequency is extremely low. Additional genetic alteration is necessary for single-step immortalization. We attempted to find out what this alteration is by overexpressing cellular signal mediator genes; c-myc and cyclin D frequently amplified in many cancer cells. Overexpression of cyclin D did not affect the immortalization, but, overexpression of c-myc along with T antigen could immortalize normal human diploid fibroblast. Several cellular markers tested during immortalization process showed that p21, a cyclin-dependent kinase inhibitor and a marker of cellular senescence, disappeared in the life span-extended cells by T antigen and in the immortalized cells by c-myc. p21 was, however, elevated in the senescent cells and in the cells of crisis. Interestingly, p16 was upregulated whenever T antigen is overexpressed. Telomerase activity was also activated only in the immortalized cells. These results suggest that overexpression of c-myc contributes to immortalization of human diploid fibroblast by activating telomerase activity and suppressing p21 activity.

Generation of Cancerous Neural Stem Cells Forming Glial Tumor by Oncogenic Stimulation

“…6), may be responsible for the oncogenic transformation induced by a combination of v-myc and H-Ras. It is currently unclear as to the manner in which hfNSCs escape from apoptosis or cell cycle arrest when v-myc is introduced to effect cellular immortalization, as v-myc expression itself is sufficient to induce apoptosis or cellular senescence in a p53-dependent manner [44–46]. It is also worth noting that the oncogenic transformation induced by v-myc and H-Ras in hfNSCs did not occur when the hfNSCs lost neural stemness as the consequence of differentiation.…”

Distinct PKC isoforms mediate cell survival and DNA synthesis in thrombin-induced myofibroblasts

“…Evidence indicates that a major target for PKC-regulated inhibition of cell cycle progression is the cyclindependent kinase inhibitor p21/Cip1/WAF1 (1,25,26,52). Activation of PKC in NIH 3T3 cells may result in elevation of p21/Cip1/WAF1, extracellular signal-regulated kinase activation, and inhibition of DNA synthesis (3).…”

Dexamethasone-induced differentiation of pancreatic AR42J cell involves p21(waf1/cip1)and MAP kinase pathway

“…The nuclear oncogene c-myc executes its multiple activities mostly through the transcriptional regulation of target genes. c-Myc is well known as a multifaceted protein that controls regulation of the cell cycle, cell growth, activities genomic instability, and stimulates angiogenesis, cell transformation, and apoptosis (Kim et al, 2001;Oster et al, 2002). At this time, it is unclear what roles are played by each of these nuclear oncogenes during the dexamethasone-induced differentiation.…”