Pattern Of Proto-oncogene Expression Research Articles

Timing of protooncogene expression varies in toxin‐induced liver regeneration

Hepatic expression of the protooncogenes c-fos and c-myc occurs within 2 h after partial hepatectomy, and these immediate early genes are thought to prime the hepatocytes for subsequent proliferation. To examine whether such gene activation occurred in the setting of hepatocyte proliferation after toxic liver injury, protooncogene expression was examined during the regenerative response following liver injury from carbon tetrachloride (CCl4) or galactosamine (GalN). The pattern of protooncogene expression after CCl4 mirrored that seen after partial hepatectomy, with rises in c-fos and c-myc mRNA content within 2 h, and then a rapid return to baseline levels. In contrast, early c-fos and c-myc expression did not occur after GalN injury. Instead GalN-induced regeneration led to a delayed, and prolonged c-fos and c-myc activation which peaked 24-48 h after injury. Increases in c-jun, jun-B, and jun-D mRNA levels also occurred in both models at times similar to the rises of c-fos and c-myc expression. Although the timing of DNA synthesis was identical after GalN or CCl4 treatment, the proliferative response after GalN injury was significantly less than that of CCl4, and marked by the histologic appearance of oval cells. The coadministration of 2-acetylaminofluorene, an inhibitor of differentiated hepatocyte proliferation, together with CCl4 altered the usual pattern of post-CCl4 protooncogene expression to one resembling that seen after GalN injury. Thus, the timing of protooncogene expression during liver regeneration may vary considerably. These variations may influence the nature of the proliferative response in terms of which cell type(s) proliferates, and the amount of regeneration that ensues.

Inhibition of abnormal T cell development and autoimmunity in gld mice by transgenic T cell receptor beta chain.

Mice homozygous for the gld (generalized lymphoproliferative disease) mutation developed systemic autoimmune disease and severe lymphadenopathy due to an age-related accumulation in the peripheral lymphoid organs of polyclonal T cells bearing a unique phenotype (CD4-CD8-TCR alpha beta+B220+). These T cells overexpress T cell receptor (TcR) alpha beta chain RNA, proto-oncogenes c-myb and fyn, and proliferate poorly in response to TcR-mediated stimulation. The origin of these T cells is poorly understood. To study the influence of a functionally rearranged TcR beta chain on the T cell developmental abnormality of the gld mutation and autoimmunity, we have backcrossed TcR V beta 8.1-transgenic mice to C3H-gld/gld to homozygosity (transgenic gld mice). In transgenic gld mice, lymphadenopathy was markedly inhibited and the accumulation of CD4-CD8- T cells did not occur, although the remaining T cells overexpressed c-myb and proliferated poorly in response to TcR occupancy. These features indicate that the pattern of proto-oncogene expression and abnormal function persist in phenotypically normal T cells in transgenic gld mice, and that these characteristics can be dissociated from the accumulation of CD4-CD8- T cells. The hypergammaglobulinemia and anti-double-stranded DNA (anti-dsDNA) antibody production was partially improved in transgenic gld mice, supporting the critical role of T cells in abnormal B cell activation described in autoimmunity-prone mice. To investigate further the mechanisms underlying the inhibition of CD4-CD8- T cell accumulation in transgenic gld mice, the fetal ontogeny of T cells in transgenic mice was compared with that of non-transgenic mice. In transgenic thymus, development of TcR alpha beta+ cells was accelerated as detected by earlier expression of CD4, CD8 and TcR in fetal thymus. In contrast, the number of TcR gamma delta+ cells was reduced. We suggest that altered T cell development in transgenic mice directly or indirectly inhibits the accumulation of abnormal T cells in gld mice.

A coordinated proto-oncogene expression characterizes MCF 247 murine leukemia virus-induced T-cell lymphomas irrespectively of proviral insertion affecting myc loci

Proto-oncogene transcriptional activation was analyzed in a group of MCF 247 MuLv-induced T-cell lymphomas to identify transformation-specific gene activations and determine whether the proviral insertion near a myc gene could promote a peculiar mechanism of transformation through a differential proto-oncogene expression pattern. Of the six lymphomas analyzed, three showed the MCF 247 provirus integrated within the N- myc locus, one carried the provirus integrated near c- myc, whereas for the remaining two, no evidence of proviral integrations in any of the known myc loci was obtained. Independently of the integrative events, the pattern of proto-oncogene expression was almost identical in all six lymphomas. These findings seem to rule out the existence of a peculiar pathway of transformation associated with the proviral insertion near a myc locus. Moreover, the transcription pattern observed was qualitatively identical to that displayed by normal thymocytes; only quantitative differences in c- or N- myc, c- myb and Ha- ras were observed. These results suggest that the T-cell proto-oncogene activation program is not qualitatively affected by the transforming event(s)

Different pattern of expression of cellular oncogenes in human non-small-cell lung cancer cell lines

Altered and deregulated cellular oncogenes were found in many human solid tumors. Except for a few types of tumors that consistently exhibited specific altered proto-oncogenes, the majority of tumors are associated with a number of transcriptionally activated cellular oncogenes. In the heterologous group of non-small-cell lung cancer (NSCLC), nothing about a specific pattern of proto-oncogene expression is known. Therefore, we investigated the expression of a panel of cellular oncogenes in NSCLC cell lines. DNA and RNA from 11 established NSCLC cell lines (4 adenocarcinoma cell lines, 3 squamous cell carcinoma cell lines, 3 large-cell carcinoma cell lines and 1 mesothelioma cell line) were isolated and analysed using the Southern, dot blot and Northern hybridization technique. c-myc RNA expression was found in all NSCLC cell line, L-myc expression only in 1 adenocarcinoma cell line, N-myc and c-myb expression in none of the 11 cell lines examined. No c-myc amplification could be detected in the DNAs. v-sis-related mRNA was observed in 5/11 cell lines without association to a specific NSCLC subtype. v-src-related mRNA, found in all tested cells, exhibited increased levels in 1 adenocarcinoma cell line (A-549) compared to the other cell lines. Binding sites for epidermal growth factor (EGF) had been described previously in NSCL, therefore we found erbB homologue transcripts coding for the EGF receptor in all NSCLC cell lines. Also, c-raf1-, N-ras-, Ki-ras-, and H-ras-related RNA expression was observed in all lines. We conclude that L-myc, N-myc, and c-myb expression does occur less frequently in NSCLC than in SCLC. Also amplification does not appear to be an important mechanism by which the c-myc proto-oncogene is activated in NSCLC. A specific pattern of oncogene expression could not be detected in NSCLC cells; each cell line examined showed its own pattern. However, transcriptional activation of a proto-oncogene like erbB, ras, raf, src, and c-myc, which are all involved in the progression pathway of EGF, may be a common feature of NSCLC.

Compensatory ovarian hypertrophy occurs by a mechanism distinct from compensatory growth in the regenerating liver

The mechanism by which compensatory ovarian growth occurs is complex and not completely understood. To compare the molecular events in compensatory ovarian growth with those known to occur in other compensatory growth processes such as the regenerating liver, the temporal pattern of proto-oncogene expression and dexoyribonucleic acid synthesis was investigated in rat ovarian tissue after unilateral castration. One hundred fifty female rats were subjected to either a left hemioophorectomy or a sham oophorectomy. Twenty-four rats from each group were put to death at 3 and 14 days after the initial procedure and the ovaries were weighed. There was a mean compensatory weight increase in the right ovaries of the hemioophorectomy group of 7.9% at 3 days and 22.5% at 14 days. The temporal pattern of proto-oncogene expression was determined by removing the right ovary from six rats in each group at 4, 8, 12, 24, 36, and 48 hours after the initial procedure. The ovaries were paired into three samples in each group for each time point and the ribonucleic acid was extracted. Dot blot hybridization was performed on each ribonucleic acid sample with radiolabeled complementary deoxyribonucleic acid probes for the proto-oncogenes c-myc, c-HA-ras, and c-fos. There was no significant increase in proto-oncogene expression in the right ovaries of the hemioophorectomy group when compared with the right ovaries of the sham oophorectomy group. The temporal pattern of dexoyribonucleic acid synthesis was determined by removing the right ovary from three rats in each group at 8, 12, 24, 36, and 48 hours after the initial procedure. Each rat had been injected intraperitoneally with [3H]thymidine 2 hours before the right oophorectomy. The specific activity of dexoyribonucleic acid extracted from each ovarian sample did not demonstrate a significant increase in ovarian dexoyribonucleic acid synthesis after hemioophorectomy or any significant difference in dexoyribonucleic acid synthesis between the hemioophorectomy and the sham oophorectomy groups. This report concludes that compensatory ovarian growth occurs by a mechanism distinct from compensatory growth in the regenerating liver.

Patterns of proto‐oncogene expression in human glioma cell lines

Previously reported studies have suggested that variations in the pattern of proto-oncogene expression within a specific tumor type may denote an underlying difference in the biology and clinical behavior of those tumors. To more sensitively characterize malignant tumors of the central nervous system, we have used Northern blot hybridization analysis to determine the patterns of expression of seven proto-oncogenes in 20 cell lines established from biopsy specimens of patients with malignant glioma. The following proto-oncogenes are expressed at detectable levels in 30 micrograms of total RNA from most glioma cell lines examined: c-myc (20/20), c-mil/raf-1 (18/18), neu (19/20), c-erbB (19/20), and c-myb (17/20). In contrast, only half of the cell lines expressed detectable c-sis (10/20). In none of the cell lines tested was N-myc (0/20) mRNA detected. Morphologic analysis of these 20 cell lines revealed three different growth patterns: bipolar, epithelial, and pleomorphic-glial. Detectable levels of c-sis mRNA typically occurred with either an epithelial or pleomorphic-glial morphology. The pleomorphic-glial subgroup was also characterized by the expression of glial fibrillary acidic protein.

Proto-oncogene expression in HL-60 cells exposed to ara-C.

To verify the reported differentiation/maturation-inducing effects of cytosine-beta-D-arabinofuranoside (ara-C, Sigma Chemical Corp, St Louis) on hematopoietic cells, we studied the morphologic changes and patterns of proto-oncogene expression in HL-60 cells that had been exposed to the drug. At the 1 X 10(-7) mol/L concentration of ara-C, approximately 10% of HL-60 cells became nitroblue tetrazolium (NBT) reduction test positive after four days exposure. However, no cells became nonspecific esterase-positive during the culture period. Doses less than 1 X 10(-8) mol/L had virtually no effect on maturation and proliferation of the target cells while doses greater than 1 X 10(-6) mol/L were lethal to HL-60 cells. Cells treated with 1 X 10(-7) mol/L and 1 X 10(-9) mol/L ara-C did not evidence any of the changes in c-myc, c-myb, c-fos, or c-fes that are noted when dimethyl sulfoxide (DMSO) or 12-0-tetradecanoyl phorbol 13-acetate (TPA, Sigma Chemical Corp, St Louis) are used to induce the differentiation of HL-60 cells. In both doses, temporary decreases of the S-phase specific and proliferation related histone H3 gene expression occurred. This phenomenon may be related to an increase in the tendency of these cells to spontaneously differentiate. Because of the possibility of drug inactivation during culture and because HL-60 cells have already matured to the promyelocytic stage, these kinds of experimental systems may be inadequate in in vitro models for low-dose ara-C therapy.

N-myc and c-src genes are differentially regulated in PCC7 embryonal carcinoma cells undergoing neuronal differentiation.

We examined the expression of N-myc, c-myc, and c-src in four embryonic carcinoma (EC) cell lines during different states of cell growth and following induction of in vitro differentiation. N-myc mRNA was detected in undifferentiated cells of four EC cell lines (PCC7, PCC3, PCC4, F9) neither of which showed N-myc gene amplification. No N-myc transcripts could be detected in mRNA prepared from a murine neuroblastoma cell line and from a murine fibroblast line. The level of N-myc mRNA decreased by 85% when PCC7 EC cells were induced by retinoic acid and cAMP treatment to form nerve-like cells. Six days after induction, the PCC7 cells changed into aggregates of neurofilament positive cells with massive neurite outgrowths. At this stage DNA replication had been reduced by more than 95%. The decreased N-myc expression in induced PCC7 cells was parallelled by 300-500% increase in c-src expression. Slowing of cell multiplication by serum starvation, on the other hand, did not affect the level of N-myc or c-src mRNA levels in PCC7 cells. C-myc was expressed in all EC lines except PCC7, which surprisingly did not express c-myc even at an exponential rate of proliferation. Chemical induction of F9 EC cells to form visceral endoderm or parietal endoderm resulted in markedly reduced (85%) levels of N-myc transcripts. A similar decline in c-myc expression was found in differentiated F9 cells. No c-src transcripts were detected in proliferating or differentiated F9 cells. These results suggest that N-myc may be expressed not only in neural development, but also in very early, undetermined embryonic cells. The activation of c-src expression when PCC7 EC cells differentiate into nerve-like cells shows that the pattern of proto-oncogene expression may change during a differentiation process, some proto-oncogenes increasing, others decreasing their representation in the mRNA pool.