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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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Related in: MedlinePlus

L6C-1 cells enter a  viable quiescent state in DM.  Flow cytofluorometric profiles of DNA content of L6  and L6C-1 nuclei stained  with propidium iodide. (A)  After 9 d in DM, cells were  stimulated by the addition of  20% FBS and harvested (B)  18 h and (C) 24 h later. Cells  were lysed with 0.1% Triton  X-100 in 0.1% sodium citrate  supplemented with 10 μg/ml  RNase and stained with 50  μg/ml propidium iodide.  DNA content of the nuclear  suspensions was determined  by FACS analysis.
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Figure 8: L6C-1 cells enter a viable quiescent state in DM. Flow cytofluorometric profiles of DNA content of L6 and L6C-1 nuclei stained with propidium iodide. (A) After 9 d in DM, cells were stimulated by the addition of 20% FBS and harvested (B) 18 h and (C) 24 h later. Cells were lysed with 0.1% Triton X-100 in 0.1% sodium citrate supplemented with 10 μg/ml RNase and stained with 50 μg/ml propidium iodide. DNA content of the nuclear suspensions was determined by FACS analysis.

Mentions: To determine the characteristics of the cell cycle arrest effected by CEA, cells from L6C-1 cultures incubated for increasing time in DM were harvested, stained with propidium iodide, and their nuclear DNA content analyzed by cytofluorometric analysis. Fig. 8 shows that the L6C-1 cells arrested exclusively with a postmitotic, preDNA synthetic G1 DNA content. Furthermore, upon addition of FBS (20%) or PDGF-BB (not shown) to these cells on day 9 in DM, DNA replication was reinitiated with a lag of 18 h (Fig. 8). The length of the 18 h lag period was unchanged after an additional 7 d (not shown), suggesting that L6C-1 cells reach a quiescent state after 9 d that does not deepen with increasing time in DM. The length of a normal G1 phase was calculated from FACS profiles of DNA content of exponentially growing L6C-1 cells, by determining the percentage of cells in either G1, S, or G2/M (Stanners and Till, 1960), giving a value of 9.6–10.0 h. A lag of 18 h therefore represents an 8 h prolongation of the normal G1 period and suggests that L6C-1 cells enter a G0-like quiescent state on or before day 9 in DM. Thus CEA expression appears to induce cells to enter a viable, reversible G0-like quiescent state that is incompatible with differentiation and permanent cell cycle withdrawal. Such a state should be susceptible to oncogenic activation.


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)

L6C-1 cells enter a  viable quiescent state in DM.  Flow cytofluorometric profiles of DNA content of L6  and L6C-1 nuclei stained  with propidium iodide. (A)  After 9 d in DM, cells were  stimulated by the addition of  20% FBS and harvested (B)  18 h and (C) 24 h later. Cells  were lysed with 0.1% Triton  X-100 in 0.1% sodium citrate  supplemented with 10 μg/ml  RNase and stained with 50  μg/ml propidium iodide.  DNA content of the nuclear  suspensions was determined  by FACS analysis.
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Related In: Results  -  Collection

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Figure 8: L6C-1 cells enter a viable quiescent state in DM. Flow cytofluorometric profiles of DNA content of L6 and L6C-1 nuclei stained with propidium iodide. (A) After 9 d in DM, cells were stimulated by the addition of 20% FBS and harvested (B) 18 h and (C) 24 h later. Cells were lysed with 0.1% Triton X-100 in 0.1% sodium citrate supplemented with 10 μg/ml RNase and stained with 50 μg/ml propidium iodide. DNA content of the nuclear suspensions was determined by FACS analysis.
Mentions: To determine the characteristics of the cell cycle arrest effected by CEA, cells from L6C-1 cultures incubated for increasing time in DM were harvested, stained with propidium iodide, and their nuclear DNA content analyzed by cytofluorometric analysis. Fig. 8 shows that the L6C-1 cells arrested exclusively with a postmitotic, preDNA synthetic G1 DNA content. Furthermore, upon addition of FBS (20%) or PDGF-BB (not shown) to these cells on day 9 in DM, DNA replication was reinitiated with a lag of 18 h (Fig. 8). The length of the 18 h lag period was unchanged after an additional 7 d (not shown), suggesting that L6C-1 cells reach a quiescent state after 9 d that does not deepen with increasing time in DM. The length of a normal G1 phase was calculated from FACS profiles of DNA content of exponentially growing L6C-1 cells, by determining the percentage of cells in either G1, S, or G2/M (Stanners and Till, 1960), giving a value of 9.6–10.0 h. A lag of 18 h therefore represents an 8 h prolongation of the normal G1 period and suggests that L6C-1 cells enter a G0-like quiescent state on or before day 9 in DM. Thus CEA expression appears to induce cells to enter a viable, reversible G0-like quiescent state that is incompatible with differentiation and permanent cell cycle withdrawal. Such a state should be susceptible to oncogenic activation.

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