Smith, Gemma Ann; (2003) Regulation of SRF activity. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The Serum Response Element (SRE) is a promoter element important in the transcriptional regulation of many immediate early and muscle specific genes. Serum Response Factor (SRF) and Ternary Complex Factor (TCF) form a complex at the c-fos SRE. TCF is phosphorylated on MAP Kinase activation resulting in activation of transcription. In addition, a TCF independent pathway, dependent on RhoA signalling and depletion of G-actin levels, activates transcription through SRF. The sensitivity of SRF target genes to inhibitors of the actin pathway correlates with the presence of a TCF binding site adjacent to the SRE. c-fos and egr-1 promoters have a TCF binding site adjacent to the SRE and are insensitive to the actin pathway, vinculin and actin promoters do not have a TCF binding site and are sensitive to the actin pathway. In this study vinculin has been used to investigate whether the presence of a TCF binding site is sufficient to render the SRE insensitive to the actin pathway. At the vinculin promoter a TCF site alone is not sufficient to reduce the sensitivity to the actin pathway inhibitor, Latrunculin B. This finding is in contrast to studies using the c-fos promoter, which can be made sensitive to the actin pathway by the removal of the TCF binding site (Murai and Treisman, 2002). The promoter context of the SRE may therefore be important in rendering a promoter insensitive to the actin pathway. However, targeting an altered DNA binding specificity TCF molecule to the SRE can inhibit the actin pathway at the vinculin promoter. In addition, a 1-hybrid screen was conducted to identify factors capable of interacting with SRF, to allow identification of the SRF co-activator of the actin pathway. A clone was identified that is not the co-activator of the actin pathway, but which may have a role in SRF mediated transcriptional activation.

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