Suppressor of Hairless Activators

Suppressor of Hairless [Su(H)] is a transcriptional regulator integral to the Notch signaling pathway, a fundamental mechanism that orchestrates cell differentiation, proliferation, and fate determination across various tissues in both invertebrates and vertebrates. The protein functions as a transcriptional effector within this pathway, directly binding to DNA and regulating the expression of target genes pivotal for developmental processes and cellular communication. Su(H)'s role is underscored by its interaction with the Notch receptor's intracellular domain (NICD), which, upon activation, translocates to the nucleus. This translocation is essential for the assembly of a transcriptional activation complex, comprising Su(H), NICD, and other coactivators, that modulates the expression of genes involved in cell fate decisions. The specificity and versatility of Su(H) in gene regulation are further refined by its ability to interact with different cofactors, thereby dictating the transcriptional outcome based on the cellular context and the state of Notch signaling.

The activation of Suppressor of Hairless is intricately tied to the activation of the Notch receptor, which undergoes proteolytic cleavage in response to ligand engagement. This cleavage releases the NICD, which then enters the nucleus and associates with Su(H). This association marks a pivotal step in the activation process, transforming Su(H) from a repressor to an activator of transcription. The transition from repression to activation is facilitated by the displacement of corepressors and the recruitment of Mastermind-like (MAML) proteins and other coactivators to the transcriptional complex. This recruitment is critical for the assembly of a transcriptionally active complex on the DNA, enabling the precise regulation of Notch target genes. The dynamic regulation by Su(H), through its ability to switch between a repressor and an activator state, exemplifies the nuanced control mechanisms that underlie the Notch signaling pathway.