摘要
Intracellular Notch (ICN) initiates DNA transcription in cooperation with CSL that acts as repressor in the absence of ICN. The ICN mediates recruitment of MAML protein, leading to the formation of minimal transcriptional complex, MAML/ICN/CSL/DNA. Crystal structure reveals that different conformations exist between the free (CSL/DNA) and bound (ICN/MAML/CSL/DNA) forms. The significance of this modulation of the CSL/DNA molecular complex can be better understood by experimental approaches that aim to elucidate the cause and timing of these events. There are four orthologues of human ICN (ICN1-4). We studied interactions between human full-length ICN1 and CSL/DNA without involvement of MAML, in vitro, and found that 1) the EMSA profile of CSL/DNA is altered in the presence of ICN1 as a consequence of an intrinsic change(s) in CSL/DNA, and not due to the formation of an ICN/CSL/DNA molecular complex;2) ICN1 destabilizes CSL/DNA. These findings indicate that human ICN1 functions to modulate the CSL/DNA molecular complex for subsequent recruitment of MAML, and that modulated CSL/DNA cannot accommodate ICN1 in the absence of MAML. The latter in turn, implies that the formation of the MAML/ICN1/CSL/DNA is likely to be a collective event, wherein preassembly of MAML and ICN1 as a binary complex co-localizes at the CSL/DNA promoter site, or the MAML/ICN1/CSL complex is pre-assembled prior to binding to the promoter, rather than ICN1 arriving at CSL/DNA ahead of MAML and/or other associated transcription factors. The novel finding that ICN1 destabilizes the CSL/DNA complex opens new possibilities of transcriptional regulation by Notch.
Intracellular Notch (ICN) initiates DNA transcription in cooperation with CSL that acts as repressor in the absence of ICN. The ICN mediates recruitment of MAML protein, leading to the formation of minimal transcriptional complex, MAML/ICN/CSL/DNA. Crystal structure reveals that different conformations exist between the free (CSL/DNA) and bound (ICN/MAML/CSL/DNA) forms. The significance of this modulation of the CSL/DNA molecular complex can be better understood by experimental approaches that aim to elucidate the cause and timing of these events. There are four orthologues of human ICN (ICN1-4). We studied interactions between human full-length ICN1 and CSL/DNA without involvement of MAML, in vitro, and found that 1) the EMSA profile of CSL/DNA is altered in the presence of ICN1 as a consequence of an intrinsic change(s) in CSL/DNA, and not due to the formation of an ICN/CSL/DNA molecular complex;2) ICN1 destabilizes CSL/DNA. These findings indicate that human ICN1 functions to modulate the CSL/DNA molecular complex for subsequent recruitment of MAML, and that modulated CSL/DNA cannot accommodate ICN1 in the absence of MAML. The latter in turn, implies that the formation of the MAML/ICN1/CSL/DNA is likely to be a collective event, wherein preassembly of MAML and ICN1 as a binary complex co-localizes at the CSL/DNA promoter site, or the MAML/ICN1/CSL complex is pre-assembled prior to binding to the promoter, rather than ICN1 arriving at CSL/DNA ahead of MAML and/or other associated transcription factors. The novel finding that ICN1 destabilizes the CSL/DNA complex opens new possibilities of transcriptional regulation by Notch.
