IER5, a DNA damage response gene, is required for Notch-mediated induction of squamous cell differentiation

Area of Science:

• Cellular biology
• Molecular oncology
• Signal transduction

Background:

• Notch signaling controls squamous cell growth and differentiation.
• Notch pathway dysregulation is common in squamous cell carcinomas, where it acts as a tumor suppressor.
• The interplay between Notch signaling and DNA damage response in squamous cells is not fully understood.

Purpose of the Study:

• To investigate how Notch signaling regulates gene expression in squamous cells.
• To identify direct Notch target genes involved in squamous cell differentiation.
• To explore the convergence of Notch and DNA damage response pathways in squamous cells.

Main Methods:

• Conditional activation of Notch signaling in squamous cells.
• Gene expression profiling to identify Notch target genes.
• Functional assays using cell lines (squamous carcinoma, keratinocytes) and purified protein systems.
• Genetic epistasis experiments and protein interaction studies.

Main Results:

• Notch activation induces a specific gene expression program via lineage-specific regulatory elements.
• IER5, a DNA damage response gene, is a direct Notch target and essential for Notch-induced differentiation.
• IER5 functions upstream of PPP2R2A (encoding PP2A B55α subunit), with which it interacts.
• Notch and DNA damage response pathways converge on shared genes promoting differentiation.

Conclusions:

• Notch and DNA damage response pathways converge on IER5 to drive squamous cell differentiation, potentially eliminating damaged cells.
• Crosstalk between Notch and protein phosphatase 2A (PP2A) integrates Notch signaling with other differentiation pathways.
• Understanding this convergence offers insights into squamous cell carcinoma development and potential therapeutic strategies.