LARP7 suppresses P-TEFb activity to inhibit breast cancer progression and metastasis.
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.
Affiliation: Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States.Show MeSH
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Mentions: Since LARP7 depletion reduces 7SK snRNA levels, leading to disruption of the 7SK snRNP and P-TEFb activation, we next investigated whether the increased P-TEFb activity was due to redistribution of P-TEFb from the inhibitory 7SK snRNP to the transcriptionally active P-TEFb complexes. Toward this goal, CKD9 was immunoprecipitated from the nuclear extracts of T47D control and LARP7 KD cells, and its associated factors were analyzed by Western blotting. LARP7 KD decreased the association of P-TEFb with the 7SK snRNP components HEXIM1 and MePCE, while increased P-TEFb binding to the SEC components AFF4, ELL2, and AF9 (Figure 6A). The increased CDK9 levels in the SEC was most likely due to the enhanced transcription of the three SEC genes as revealed by qRT-PCR (Figure 6B), which in turn resulted in elevated levels of these proteins in the nuclear extracts (Figure 6A). Thus, LARP7 KD releases P-TEFb from the 7SK snRNP and redistributes it to the active SEC.10.7554/eLife.02907.011Figure 6.Silencing LARP7 redistributes P-TEFb from the 7SK snRNP to SEC.
Affiliation: Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States.