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LARP7 suppresses P-TEFb activity to inhibit breast cancer progression and metastasis.

Ji X, Lu H, Zhou Q, Luo K - Elife (2014)

Bottom Line: The positive transcription elongation factor b (P-TEFb) stimulates transcriptional elongation by phosphorylating Pol II and antagonizing negative elongation factors.A reservoir of P-TEFb is sequestered in the inactive 7SK snRNP where 7SK snRNA and the La-related protein LARP7 are required for the integrity of this complex.Decreased levels of LARP7 and 7SK snRNA redistribute P-TEFb to the transcriptionally active super elongation complex, resulting in P-TEFb activation and increased transcription of EMT transcription factors, including Slug, FOXC2, ZEB2, and Twist1, to promote breast cancer EMT, invasion, and metastasis.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States.

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Inhibition of P-TEFb impairs EMT and survival of metastatic MDA-MB-231 cells.(A) Treatment of MDA-MB-231 cells with 0.3 μM flavopiridol (Flvp) significantly impairs cell migration as shown by the Transwell assay. The p value (*p<0.05) was determined by the Student's t test. (B) qRT-PCR analysis of Slug expression in MDA-MB-231 cells that have been treated with flavopiridol for 7 hr at the indicated concentrations. (C and D) Clonogenic growth assay. MDA-MB-231 cells were transfected with control vector, Flag-tagged WT LARP7, or Δ2A mutant. The expression of LARP7 and Δ2A was confirmed by Western blotting with anti-Flag. (C). (D) Representative culture areas are shown in the top panel. The number of colonies was quantified and shown in the graph below. The p value (*p<0.05) was determined by the Student's t test.DOI:http://dx.doi.org/10.7554/eLife.02907.012
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fig7: Inhibition of P-TEFb impairs EMT and survival of metastatic MDA-MB-231 cells.(A) Treatment of MDA-MB-231 cells with 0.3 μM flavopiridol (Flvp) significantly impairs cell migration as shown by the Transwell assay. The p value (*p<0.05) was determined by the Student's t test. (B) qRT-PCR analysis of Slug expression in MDA-MB-231 cells that have been treated with flavopiridol for 7 hr at the indicated concentrations. (C and D) Clonogenic growth assay. MDA-MB-231 cells were transfected with control vector, Flag-tagged WT LARP7, or Δ2A mutant. The expression of LARP7 and Δ2A was confirmed by Western blotting with anti-Flag. (C). (D) Representative culture areas are shown in the top panel. The number of colonies was quantified and shown in the graph below. The p value (*p<0.05) was determined by the Student's t test.DOI:http://dx.doi.org/10.7554/eLife.02907.012

Mentions: If LARP7 downregulation accelerates malignant progression by increasing expression of EMT genes through elevated P-TEFb activity, we should expect P-TEFb inhibition or re-introduction of LARP7 protein to block EMT and transformation. To test this hypothesis, we first treated the highly invasive and metastatic MDA-MB-231 breast cancer cells with flavopiridol and noted that the treatment significantly inhibited cell migration (Figure 7A). Furthermore, mRNA levels of Slug, a major EMT regulator, were repressed in a dose-dependent manner upon P-TEFb inhibition (Figure 7B). These data suggest that inhibition of P-TEFb can effectively block cell migration in metastatic breast cancer cells.10.7554/eLife.02907.012Figure 7.Inhibition of P-TEFb impairs EMT and survival of metastatic MDA-MB-231 cells.


LARP7 suppresses P-TEFb activity to inhibit breast cancer progression and metastasis.

Ji X, Lu H, Zhou Q, Luo K - Elife (2014)

Inhibition of P-TEFb impairs EMT and survival of metastatic MDA-MB-231 cells.(A) Treatment of MDA-MB-231 cells with 0.3 μM flavopiridol (Flvp) significantly impairs cell migration as shown by the Transwell assay. The p value (*p<0.05) was determined by the Student's t test. (B) qRT-PCR analysis of Slug expression in MDA-MB-231 cells that have been treated with flavopiridol for 7 hr at the indicated concentrations. (C and D) Clonogenic growth assay. MDA-MB-231 cells were transfected with control vector, Flag-tagged WT LARP7, or Δ2A mutant. The expression of LARP7 and Δ2A was confirmed by Western blotting with anti-Flag. (C). (D) Representative culture areas are shown in the top panel. The number of colonies was quantified and shown in the graph below. The p value (*p<0.05) was determined by the Student's t test.DOI:http://dx.doi.org/10.7554/eLife.02907.012
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fig7: Inhibition of P-TEFb impairs EMT and survival of metastatic MDA-MB-231 cells.(A) Treatment of MDA-MB-231 cells with 0.3 μM flavopiridol (Flvp) significantly impairs cell migration as shown by the Transwell assay. The p value (*p<0.05) was determined by the Student's t test. (B) qRT-PCR analysis of Slug expression in MDA-MB-231 cells that have been treated with flavopiridol for 7 hr at the indicated concentrations. (C and D) Clonogenic growth assay. MDA-MB-231 cells were transfected with control vector, Flag-tagged WT LARP7, or Δ2A mutant. The expression of LARP7 and Δ2A was confirmed by Western blotting with anti-Flag. (C). (D) Representative culture areas are shown in the top panel. The number of colonies was quantified and shown in the graph below. The p value (*p<0.05) was determined by the Student's t test.DOI:http://dx.doi.org/10.7554/eLife.02907.012
Mentions: If LARP7 downregulation accelerates malignant progression by increasing expression of EMT genes through elevated P-TEFb activity, we should expect P-TEFb inhibition or re-introduction of LARP7 protein to block EMT and transformation. To test this hypothesis, we first treated the highly invasive and metastatic MDA-MB-231 breast cancer cells with flavopiridol and noted that the treatment significantly inhibited cell migration (Figure 7A). Furthermore, mRNA levels of Slug, a major EMT regulator, were repressed in a dose-dependent manner upon P-TEFb inhibition (Figure 7B). These data suggest that inhibition of P-TEFb can effectively block cell migration in metastatic breast cancer cells.10.7554/eLife.02907.012Figure 7.Inhibition of P-TEFb impairs EMT and survival of metastatic MDA-MB-231 cells.

Bottom Line: The positive transcription elongation factor b (P-TEFb) stimulates transcriptional elongation by phosphorylating Pol II and antagonizing negative elongation factors.A reservoir of P-TEFb is sequestered in the inactive 7SK snRNP where 7SK snRNA and the La-related protein LARP7 are required for the integrity of this complex.Decreased levels of LARP7 and 7SK snRNA redistribute P-TEFb to the transcriptionally active super elongation complex, resulting in P-TEFb activation and increased transcription of EMT transcription factors, including Slug, FOXC2, ZEB2, and Twist1, to promote breast cancer EMT, invasion, and metastasis.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States.

Show MeSH
Related in: MedlinePlus