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Abstract:
γ-Protocadherins (γ-pcdhs) are type I membrane-spanning glycoproteins, widely expressed in the mammal and required for survival. These cell adhesion molecules are expressed from a complex locus comprising 22 functional variable exons arranged in tandem, each encoding extracellular, transmembrane and intracellular sequence, and three exons for an invariant C-terminal domain (γ-ICD). However, the signaling mechanisms that lie downstream of γ-pcdhs have not been elucidated. Here we report that γ-pcdhs are subject to presenilin-dependent intramembrane cleavage (PS-IP), accompanied by shedding of the extracellular domain. The cleaved intracellular domain (γ-ICD) translocates to the cell nucleus and was detected in subsets of cortical neurons. Notably, gene-targeted mice lacking functional γ-ICD sequence showed severely reduced γ-pcdh mRNA levels and neonatal lethality. Most importantly, inhibition of γ-secretase decreased γ-pcdh locus expression. Luciferase reporter assays demonstrated that γ-pcdh promoter activity is increased by γ-ICD. These results reveal an intracellular signaling mechanism for γ-pcdhs and identify a novel vital target for the γ-secretase complex.
