Elucidation of the physical and functional interactions between the MEIS1A and the CREB and CRTC transcription factors
Date of Issue2012
School of Biological Sciences
Myeloid ecotropic viral integration site 1 (MEIS1), a member of the TALE class of homeodomain-containing transcription factors, is a co-factor for HOX and PBX proteins. Together, these regulators are involved in patterning the anteroposterior axis and limbs of developing embryos, organogenesis, hematopoiesis and cancer. Recent findings revealed that the MEIS1A C-terminus harbors a transcriptional activation domain that is responsive to protein kinase-A (PKA) signaling and dependent on the co-activator CREB-binding protein (CBP). This same C-terminus that harbors the transcriptional activation domain and is responsive to PKA signaling has also been shown to mediate MEIS1A oncogenicity. This thesis seeks to extend our current understanding of the mechanisms by which the MEIS1A C-terminus exerts its transactivation function. We describe here the involvement of CREB and its coactivators CBP and CRTC in contributing to the PKA responsiveness at the MEIS1A C-terminus. Our studies revealed an ability of CRTC to bypass PKA for transactivation at the MEIS1A C-terminus. We have also demonstrated physical interaction between CRTC and MEIS proteins and have mapped the domain in CRTC that interacts with MEIS to the N-terminal coiled-coil region. Further chromatin immunoprecipitation confirmed co-occupancy of MEIS1, CRTC2 and PBX1 proteins on MEIS1 target genes. With the use of CREB mutants ACREB and ACREBR314, I determined the importance of CREB to the activity of MEIS1A. By means of proximity ligation assay, I have further established endogenous interactions between MEIS-CRTC, MEIS-CREB and MEIS-CBP. These findings strongly implicate the MEIS1A C-terminus in binding and functionally interacting with CREB and CRTC. I have also attempted to elucidate the structure of the MEIS and CRTC proteins in the hope of understanding how the proteins interact to function during development. I have in this thesis identified a cooperative role of MEIS, CREB and CRTC interaction, where CRTC with the help of CREB physically cooperates with MEIS to achieve PKA-inducible transactivation through the MEIS1A C-terminus, implicating the concerted action of these proteins in developmental processes.