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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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Differentiation in the nonproliferating centers of cell colonies. (A) Photomicrographs of colonies arising from cells  seeded at clonal density and grown for 10 d  in GM. Representative parental (P) and  v-Myc+ (M) colonies, showing the presence of myotubes in the centers of only  v-Myc+ colonies. (B) Lower magnification of plates from (A). (C) The percentage of colonies showing myotubes. Colonies arising after 10-d incubations in GM  were scored for the presence of myotubes.  Average results for two, and for some  lines three, experiments are shown. The  plating efficiencies for colony formation  varied from 50 to 92% between individual  experiments and varied no more than 10%  between cell lines in a given experiment.  Bar: (A) 0.4 mm; (B) 1.7 mm.
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Figure 4: Differentiation in the nonproliferating centers of cell colonies. (A) Photomicrographs of colonies arising from cells seeded at clonal density and grown for 10 d in GM. Representative parental (P) and v-Myc+ (M) colonies, showing the presence of myotubes in the centers of only v-Myc+ colonies. (B) Lower magnification of plates from (A). (C) The percentage of colonies showing myotubes. Colonies arising after 10-d incubations in GM were scored for the presence of myotubes. Average results for two, and for some lines three, experiments are shown. The plating efficiencies for colony formation varied from 50 to 92% between individual experiments and varied no more than 10% between cell lines in a given experiment. Bar: (A) 0.4 mm; (B) 1.7 mm.

Mentions: On day 5, cultures expressing ectopic Myc alone began to acidify the medium and display cell death. Coincident with this, marked cell elongation and alignment and the formation of multinucleated myotubes were also apparent. These changes are reflected in the complete loss of viability as measured by colony-forming ability after 15 d in culture (Fig. 2, inset) and in the increase in average size of M cells nearing saturation (Fig. 3). To investigate the effect of v-Myc on differentiation, P and M cells were tested in two different assays in which serum growth factors become limiting. First, we quantified the effect of growth factor depletion in the nonproliferating centers of cell colonies (Fig. 4). 75% of M colonies, obtained by plating viable M cells from the exponential growth phase, showed myotubes in their centers after 10 d of incubation in GM, whereas P colonies showed no myotubes under these conditions (Fig. 4), thus indicating a dramatic increase in the propensity for differentiation. Second, cells were seeded directly into DM and stained 4 d later. In spite of significant cell loss that reduced the cell density of M cultures, M cells formed myotubes; in this case P cells, as expected, readily differentiated (Fig. 5 A, compare M and P).


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)

Differentiation in the nonproliferating centers of cell colonies. (A) Photomicrographs of colonies arising from cells  seeded at clonal density and grown for 10 d  in GM. Representative parental (P) and  v-Myc+ (M) colonies, showing the presence of myotubes in the centers of only  v-Myc+ colonies. (B) Lower magnification of plates from (A). (C) The percentage of colonies showing myotubes. Colonies arising after 10-d incubations in GM  were scored for the presence of myotubes.  Average results for two, and for some  lines three, experiments are shown. The  plating efficiencies for colony formation  varied from 50 to 92% between individual  experiments and varied no more than 10%  between cell lines in a given experiment.  Bar: (A) 0.4 mm; (B) 1.7 mm.
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Related In: Results  -  Collection

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Figure 4: Differentiation in the nonproliferating centers of cell colonies. (A) Photomicrographs of colonies arising from cells seeded at clonal density and grown for 10 d in GM. Representative parental (P) and v-Myc+ (M) colonies, showing the presence of myotubes in the centers of only v-Myc+ colonies. (B) Lower magnification of plates from (A). (C) The percentage of colonies showing myotubes. Colonies arising after 10-d incubations in GM were scored for the presence of myotubes. Average results for two, and for some lines three, experiments are shown. The plating efficiencies for colony formation varied from 50 to 92% between individual experiments and varied no more than 10% between cell lines in a given experiment. Bar: (A) 0.4 mm; (B) 1.7 mm.
Mentions: On day 5, cultures expressing ectopic Myc alone began to acidify the medium and display cell death. Coincident with this, marked cell elongation and alignment and the formation of multinucleated myotubes were also apparent. These changes are reflected in the complete loss of viability as measured by colony-forming ability after 15 d in culture (Fig. 2, inset) and in the increase in average size of M cells nearing saturation (Fig. 3). To investigate the effect of v-Myc on differentiation, P and M cells were tested in two different assays in which serum growth factors become limiting. First, we quantified the effect of growth factor depletion in the nonproliferating centers of cell colonies (Fig. 4). 75% of M colonies, obtained by plating viable M cells from the exponential growth phase, showed myotubes in their centers after 10 d of incubation in GM, whereas P colonies showed no myotubes under these conditions (Fig. 4), thus indicating a dramatic increase in the propensity for differentiation. Second, cells were seeded directly into DM and stained 4 d later. In spite of significant cell loss that reduced the cell density of M cultures, M cells formed myotubes; in this case P cells, as expected, readily differentiated (Fig. 5 A, compare M and P).

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