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. 2006 Mar 16;25(7):1522–1533. doi: 10.1038/sj.emboj.7601040

Figure 8.

Figure 8

Model for activation of pol III transcription following induction of hypertrophic growth. Hypertrophic stimulation leads to the rapid activation of Erk and c-Myc, which are likely to target TFIIIB directly (as documented in other cell types), leading to the initial induction of pol III transcription. However, limiting levels of Brf1, and sequestration of TFIIIB by hypophosphorylated RB, may restrict the extent to which these molecules activate transcription at early time points. The increase in Brf1 abundance by 6 h, and the subsequent hyperphosphorylation of RB, would relieve these restrictions, thus allowing maximum pol III output. Decreased c-Myc levels and RB dephosphorylation might account for the downregulation of pol III transcription occurring 24–48 h after hypertrophic stimulation. Abbreviations used: TFIIIB, IIIB; TFIIIC, IIIC; c-Myc, Myc. Bold arrows below transcription complexes indicate active class III gene transcription; dashed arrows indicate transcription at a reduced rate.