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Polycomb group protein Bmi1 is required for growth of RAF driven non-small-cell lung cancer.

Becker M, Korn C, Sienerth AR, Voswinckel R, Luetkenhaus K, Ceteci F, Rapp UR - PLoS ONE (2009)

Bottom Line: In order to evaluate Bmi1 function in NSCLC two founder lines that differ in incidence and latency of tumor formation were compared.Ablation of Bmi1 expression in both lines had a dramatically decreased tumor growth.Reduction in tumor growth resulted from an increase in cell death and decrease in cell cycle progression that corresponded with up-regulation of the p16(INK4a) and p19(ARF).

View Article: PubMed Central - PubMed

Affiliation: Bayerisches Krebsforschungszentrum, University of Wuerzburg, Wuerzburg, Germany.

ABSTRACT

Background: We have previously described a RAF oncogene driven transgenic mouse model for non small cell lung cancer (NSCLC). Here we examine whether tumor initiation and growth requires the stem cell self-renewal factor Bmi1.

Principal findings: In order to evaluate Bmi1 function in NSCLC two founder lines that differ in incidence and latency of tumor formation were compared. Ablation of Bmi1 expression in both lines had a dramatically decreased tumor growth. As the line with shorter latency matched the life span of Bmi1 knock out mice, these mice were chosen for further study. The absence of Bmi1 did not decrease the number of tumor initiation in these mice as only the size and not the number of tumors decreased. Reduction in tumor growth resulted from an increase in cell death and decrease in cell cycle progression that corresponded with up-regulation of the p16(INK4a) and p19(ARF).

Significance: The data identifies Bmi1 as an important factor for expansion but not initiation of RAF driven NSCLC.

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Related in: MedlinePlus

Increased apoptosis and reduced proliferation in Bmi1−/−BXB11 tumors.A) TUNEL staining of paraffin embedded lung sections from Bmi1−/−BXB11 and BXB11 mice. DNase I treated lung sections were used as positive control. Sections treated without terminal deoxynucleotidyl transferase served as negative control. Dotted white lines delineate tumors. Genotypes and ages as indicated. Arrows indicate apoptotic (green) cells. Scale bar = 30 µm. B) Ki67 (red)/pro SP-C (green) co- immunofluorescence staining of lung sections from BXB11 and Bmi1−/−BXB11 mice. Arrows indicate cycling tumor cells. “*” indicates staining artifact. Scale bar = 30 µm. C) Quantification of TUNEL positive cells in lung tumors of two weeks and three months old BXB11 and Bmi1−/−BXB11 mice (n = 4 animals per genotype), for details see materials and methods. Data presented as Box-and-Whiskers plot for details of data presentation see figure legend of Figure 1. D) Quantification of Ki-67/pro SP-C double positive cells. At least five tumors from five different animals were analyzed. p-values were calculated using Student's t-test, only p-values indicating significance are shown.
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pone-0004230-g003: Increased apoptosis and reduced proliferation in Bmi1−/−BXB11 tumors.A) TUNEL staining of paraffin embedded lung sections from Bmi1−/−BXB11 and BXB11 mice. DNase I treated lung sections were used as positive control. Sections treated without terminal deoxynucleotidyl transferase served as negative control. Dotted white lines delineate tumors. Genotypes and ages as indicated. Arrows indicate apoptotic (green) cells. Scale bar = 30 µm. B) Ki67 (red)/pro SP-C (green) co- immunofluorescence staining of lung sections from BXB11 and Bmi1−/−BXB11 mice. Arrows indicate cycling tumor cells. “*” indicates staining artifact. Scale bar = 30 µm. C) Quantification of TUNEL positive cells in lung tumors of two weeks and three months old BXB11 and Bmi1−/−BXB11 mice (n = 4 animals per genotype), for details see materials and methods. Data presented as Box-and-Whiskers plot for details of data presentation see figure legend of Figure 1. D) Quantification of Ki-67/pro SP-C double positive cells. At least five tumors from five different animals were analyzed. p-values were calculated using Student's t-test, only p-values indicating significance are shown.

Mentions: The strongly reduced tumor growth and the loss of tumors over time in both founder lines with abrogated Bmi1 expression is either a consequence of a block in cell cycle progression or increased cell death or a combination of both. Bmi1 has previously been implicated in promoting tumor cell survival and cell cycle progression in a tissue culture model system [25], [26]. TUNEL staining showed a significant increase in the apoptotic cell ratio in adenomas of three months old Bmi1−/−BXB11 mice (Figure 3A and 3C). This indicates that apoptosis is a late event in Bmi1−/−BXB11 adenomas. Next we examined growth rate. We performed Ki-67/pro SP-C co-staining on lungs prepared from two weeks and three months old Bmi1−/−BXB11 and BXB11 animals. The fraction of cells in cycle is strongly reduced upon Bmi1 ablation. Moreover as evident from the BXB11 control at the age of three months the rate of growth of these tumors has also decreased suggesting either a limited replicative lifespan for BXB11 transformed AT2 cells or other levels of growth control (Figure 3B and 3D).


Polycomb group protein Bmi1 is required for growth of RAF driven non-small-cell lung cancer.

Becker M, Korn C, Sienerth AR, Voswinckel R, Luetkenhaus K, Ceteci F, Rapp UR - PLoS ONE (2009)

Increased apoptosis and reduced proliferation in Bmi1−/−BXB11 tumors.A) TUNEL staining of paraffin embedded lung sections from Bmi1−/−BXB11 and BXB11 mice. DNase I treated lung sections were used as positive control. Sections treated without terminal deoxynucleotidyl transferase served as negative control. Dotted white lines delineate tumors. Genotypes and ages as indicated. Arrows indicate apoptotic (green) cells. Scale bar = 30 µm. B) Ki67 (red)/pro SP-C (green) co- immunofluorescence staining of lung sections from BXB11 and Bmi1−/−BXB11 mice. Arrows indicate cycling tumor cells. “*” indicates staining artifact. Scale bar = 30 µm. C) Quantification of TUNEL positive cells in lung tumors of two weeks and three months old BXB11 and Bmi1−/−BXB11 mice (n = 4 animals per genotype), for details see materials and methods. Data presented as Box-and-Whiskers plot for details of data presentation see figure legend of Figure 1. D) Quantification of Ki-67/pro SP-C double positive cells. At least five tumors from five different animals were analyzed. p-values were calculated using Student's t-test, only p-values indicating significance are shown.
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Related In: Results  -  Collection

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pone-0004230-g003: Increased apoptosis and reduced proliferation in Bmi1−/−BXB11 tumors.A) TUNEL staining of paraffin embedded lung sections from Bmi1−/−BXB11 and BXB11 mice. DNase I treated lung sections were used as positive control. Sections treated without terminal deoxynucleotidyl transferase served as negative control. Dotted white lines delineate tumors. Genotypes and ages as indicated. Arrows indicate apoptotic (green) cells. Scale bar = 30 µm. B) Ki67 (red)/pro SP-C (green) co- immunofluorescence staining of lung sections from BXB11 and Bmi1−/−BXB11 mice. Arrows indicate cycling tumor cells. “*” indicates staining artifact. Scale bar = 30 µm. C) Quantification of TUNEL positive cells in lung tumors of two weeks and three months old BXB11 and Bmi1−/−BXB11 mice (n = 4 animals per genotype), for details see materials and methods. Data presented as Box-and-Whiskers plot for details of data presentation see figure legend of Figure 1. D) Quantification of Ki-67/pro SP-C double positive cells. At least five tumors from five different animals were analyzed. p-values were calculated using Student's t-test, only p-values indicating significance are shown.
Mentions: The strongly reduced tumor growth and the loss of tumors over time in both founder lines with abrogated Bmi1 expression is either a consequence of a block in cell cycle progression or increased cell death or a combination of both. Bmi1 has previously been implicated in promoting tumor cell survival and cell cycle progression in a tissue culture model system [25], [26]. TUNEL staining showed a significant increase in the apoptotic cell ratio in adenomas of three months old Bmi1−/−BXB11 mice (Figure 3A and 3C). This indicates that apoptosis is a late event in Bmi1−/−BXB11 adenomas. Next we examined growth rate. We performed Ki-67/pro SP-C co-staining on lungs prepared from two weeks and three months old Bmi1−/−BXB11 and BXB11 animals. The fraction of cells in cycle is strongly reduced upon Bmi1 ablation. Moreover as evident from the BXB11 control at the age of three months the rate of growth of these tumors has also decreased suggesting either a limited replicative lifespan for BXB11 transformed AT2 cells or other levels of growth control (Figure 3B and 3D).

Bottom Line: In order to evaluate Bmi1 function in NSCLC two founder lines that differ in incidence and latency of tumor formation were compared.Ablation of Bmi1 expression in both lines had a dramatically decreased tumor growth.Reduction in tumor growth resulted from an increase in cell death and decrease in cell cycle progression that corresponded with up-regulation of the p16(INK4a) and p19(ARF).

View Article: PubMed Central - PubMed

Affiliation: Bayerisches Krebsforschungszentrum, University of Wuerzburg, Wuerzburg, Germany.

ABSTRACT

Background: We have previously described a RAF oncogene driven transgenic mouse model for non small cell lung cancer (NSCLC). Here we examine whether tumor initiation and growth requires the stem cell self-renewal factor Bmi1.

Principal findings: In order to evaluate Bmi1 function in NSCLC two founder lines that differ in incidence and latency of tumor formation were compared. Ablation of Bmi1 expression in both lines had a dramatically decreased tumor growth. As the line with shorter latency matched the life span of Bmi1 knock out mice, these mice were chosen for further study. The absence of Bmi1 did not decrease the number of tumor initiation in these mice as only the size and not the number of tumors decreased. Reduction in tumor growth resulted from an increase in cell death and decrease in cell cycle progression that corresponded with up-regulation of the p16(INK4a) and p19(ARF).

Significance: The data identifies Bmi1 as an important factor for expansion but not initiation of RAF driven NSCLC.

Show MeSH
Related in: MedlinePlus