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Carcinoembryonic antigen, a human tumor marker, cooperates with Myc and Bcl-2 in cellular transformation.

Screaton RA, Penn LZ, Stanners CP - J. Cell Biol. (1997)

Bottom Line: The further expression of CEA has a dominant effect in blocking differentiation, regardless of the presence of the other activated oncogenes, generating cells that enter a reversible quiescent G0-like state in medium promoting differentiation.Transfectants expressing CEA with or without v-myc and bcl-2 allow the emergence of cells with the property of heritable, efficient, anchorage-independent growth in soft agar and the ability to markedly reduce the latency for tumor formation in nude mice.We propose that by prolonging cell survival in the presence of differentiation signals, CEA represents a novel class of dominant differentiation-blocking oncogene.

View Article: PubMed Central - PubMed

Affiliation: McGill Cancer Centre and Department of Biochemistry, McGill University, Montreal, Quebec, Canada H3G 1Y6.

ABSTRACT
Carcinoembryonic antigen (CEA) is a tumor marker that is overexpressed in many human cancers and functions in vitro as a homotypic intercellular adhesion molecule. We have investigated the possibility of synergy between CEA, v-Myc, and Bcl-2 in the transformation of cells with differentiation capacity. We find that v-Myc increases the cell division rate and maximum density of rat L6 myoblasts but also markedly stimulates both apoptosis and surprisingly, differentiation, thus preventing transformation. The superposition of Bcl-2 blocks the apoptotic stimulation of v-Myc and independently promotes further cell division at confluence, but still allows differentiation. The further expression of CEA has a dominant effect in blocking differentiation, regardless of the presence of the other activated oncogenes, generating cells that enter a reversible quiescent G0-like state in medium promoting differentiation. Transfectants expressing CEA with or without v-myc and bcl-2 allow the emergence of cells with the property of heritable, efficient, anchorage-independent growth in soft agar and the ability to markedly reduce the latency for tumor formation in nude mice. We propose that by prolonging cell survival in the presence of differentiation signals, CEA represents a novel class of dominant differentiation-blocking oncogene.

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Frequency of apoptosis of L6 transfectants in  DM. (A) Electron micrograph showing chromatin  condensation and compaction at the periphery of the  nuclear membrane characteristic of apoptosis in L6  v-Myc+ cells incubated under low serum conditions.  (B) The percentage of nuclei  in L6 transfectant cultures  demonstrating chromatin  condensation when stained  with orcein. Subconfluent  cultures in GM were washed  and incubated in DM for 24 h  before fixation and staining  with orcein. Results are representative of several independent experiments. Two  cell suspensions and three  fields per cell suspension  were scored, and the results  were averaged. Photomicrographs of subconfluent (C)  parental L6 and (D) v-Myc+  cells stained with orcein showing condensation of chromatin and damaged nuclei (arrows) in v-Myc+ cells. Bar:  (A) 4 μm; (C and D) 40 μm.
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Figure 6: Frequency of apoptosis of L6 transfectants in DM. (A) Electron micrograph showing chromatin condensation and compaction at the periphery of the nuclear membrane characteristic of apoptosis in L6 v-Myc+ cells incubated under low serum conditions. (B) The percentage of nuclei in L6 transfectant cultures demonstrating chromatin condensation when stained with orcein. Subconfluent cultures in GM were washed and incubated in DM for 24 h before fixation and staining with orcein. Results are representative of several independent experiments. Two cell suspensions and three fields per cell suspension were scored, and the results were averaged. Photomicrographs of subconfluent (C) parental L6 and (D) v-Myc+ cells stained with orcein showing condensation of chromatin and damaged nuclei (arrows) in v-Myc+ cells. Bar: (A) 4 μm; (C and D) 40 μm.

Mentions: The increased cell mortality in response to depletion of growth factors was suggestive of an apoptotic response, as seen with Rat-1 fibroblasts overexpressing c-myc (Evan et al., 1992). To maximize cell death and minimize myotube formation, cells were grown in GM until one day before confluence, when the medium was changed to DM. After 24 h of incubation in DM, 40% of subconfluent M cells compared to 6% of P cells displayed condensed chromatin and damaged nuclei, hallmarks of apoptotic cell death as confirmed by electron microscopy (Fig. 6) by the degradation of DNA into discrete bands visible as a “ladder” on electrophoretic gels (data not shown) and by the fact that coexpression of Bcl-2 abrogated the myc-induced increase. The remaining M cells were sparse but multinucleated, indicative of myogenic fusion (Fig. 5 A).


Carcinoembryonic antigen, a human tumor marker, cooperates with Myc and Bcl-2 in cellular transformation.

Screaton RA, Penn LZ, Stanners CP - J. Cell Biol. (1997)

Frequency of apoptosis of L6 transfectants in  DM. (A) Electron micrograph showing chromatin  condensation and compaction at the periphery of the  nuclear membrane characteristic of apoptosis in L6  v-Myc+ cells incubated under low serum conditions.  (B) The percentage of nuclei  in L6 transfectant cultures  demonstrating chromatin  condensation when stained  with orcein. Subconfluent  cultures in GM were washed  and incubated in DM for 24 h  before fixation and staining  with orcein. Results are representative of several independent experiments. Two  cell suspensions and three  fields per cell suspension  were scored, and the results  were averaged. Photomicrographs of subconfluent (C)  parental L6 and (D) v-Myc+  cells stained with orcein showing condensation of chromatin and damaged nuclei (arrows) in v-Myc+ cells. Bar:  (A) 4 μm; (C and D) 40 μm.
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Related In: Results  -  Collection

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Figure 6: Frequency of apoptosis of L6 transfectants in DM. (A) Electron micrograph showing chromatin condensation and compaction at the periphery of the nuclear membrane characteristic of apoptosis in L6 v-Myc+ cells incubated under low serum conditions. (B) The percentage of nuclei in L6 transfectant cultures demonstrating chromatin condensation when stained with orcein. Subconfluent cultures in GM were washed and incubated in DM for 24 h before fixation and staining with orcein. Results are representative of several independent experiments. Two cell suspensions and three fields per cell suspension were scored, and the results were averaged. Photomicrographs of subconfluent (C) parental L6 and (D) v-Myc+ cells stained with orcein showing condensation of chromatin and damaged nuclei (arrows) in v-Myc+ cells. Bar: (A) 4 μm; (C and D) 40 μm.
Mentions: The increased cell mortality in response to depletion of growth factors was suggestive of an apoptotic response, as seen with Rat-1 fibroblasts overexpressing c-myc (Evan et al., 1992). To maximize cell death and minimize myotube formation, cells were grown in GM until one day before confluence, when the medium was changed to DM. After 24 h of incubation in DM, 40% of subconfluent M cells compared to 6% of P cells displayed condensed chromatin and damaged nuclei, hallmarks of apoptotic cell death as confirmed by electron microscopy (Fig. 6) by the degradation of DNA into discrete bands visible as a “ladder” on electrophoretic gels (data not shown) and by the fact that coexpression of Bcl-2 abrogated the myc-induced increase. The remaining M cells were sparse but multinucleated, indicative of myogenic fusion (Fig. 5 A).

Bottom Line: The further expression of CEA has a dominant effect in blocking differentiation, regardless of the presence of the other activated oncogenes, generating cells that enter a reversible quiescent G0-like state in medium promoting differentiation.Transfectants expressing CEA with or without v-myc and bcl-2 allow the emergence of cells with the property of heritable, efficient, anchorage-independent growth in soft agar and the ability to markedly reduce the latency for tumor formation in nude mice.We propose that by prolonging cell survival in the presence of differentiation signals, CEA represents a novel class of dominant differentiation-blocking oncogene.

View Article: PubMed Central - PubMed

Affiliation: McGill Cancer Centre and Department of Biochemistry, McGill University, Montreal, Quebec, Canada H3G 1Y6.

ABSTRACT
Carcinoembryonic antigen (CEA) is a tumor marker that is overexpressed in many human cancers and functions in vitro as a homotypic intercellular adhesion molecule. We have investigated the possibility of synergy between CEA, v-Myc, and Bcl-2 in the transformation of cells with differentiation capacity. We find that v-Myc increases the cell division rate and maximum density of rat L6 myoblasts but also markedly stimulates both apoptosis and surprisingly, differentiation, thus preventing transformation. The superposition of Bcl-2 blocks the apoptotic stimulation of v-Myc and independently promotes further cell division at confluence, but still allows differentiation. The further expression of CEA has a dominant effect in blocking differentiation, regardless of the presence of the other activated oncogenes, generating cells that enter a reversible quiescent G0-like state in medium promoting differentiation. Transfectants expressing CEA with or without v-myc and bcl-2 allow the emergence of cells with the property of heritable, efficient, anchorage-independent growth in soft agar and the ability to markedly reduce the latency for tumor formation in nude mice. We propose that by prolonging cell survival in the presence of differentiation signals, CEA represents a novel class of dominant differentiation-blocking oncogene.

Show MeSH
Related in: MedlinePlus