Presenilin-dependent processing and nuclear function of gamma-protocadherins

Area of Science:

• Neuroscience
• Molecular Biology
• Biochemistry

Background:

• Protocadherin gene clusters encode cadherin-related proteins crucial for the vertebrate nervous system.
• Gamma-protocadherins are type-I transmembrane proteins with roles in neural development and function.

Purpose of the Study:

• To investigate the proteolytic processing of gamma-protocadherins.
• To elucidate the role of presenilin and gamma-secretase in this processing.
• To determine the cellular localization and stability of resulting fragments.

Main Methods:

• Biochemical assays to study protein cleavage.
• Use of presenilin inhibitors (L685,458) and knockout murine embryonic fibroblasts.
• Analysis of fragment stability and degradation pathways (proteasomal).
• Subcellular localization studies.

Main Results:

• Gamma-protocadherins are cleaved by a metalloproteinase, releasing soluble extracellular and membrane-associated carboxyl-terminal fragments.
• Presenilin (gamma-secretase) further cleaves the carboxyl-terminal fragment.
• Fragment accumulation occurs upon gamma-secretase inhibition or deficiency.
• The gamma-secretase-generated fragment is unstable but accumulates with proteasomal inhibition.
• The proteolytic fragment can translocate to the nucleus.

Conclusions:

• Gamma-protocadherin processing is regulated by sequential proteolytic events involving metalloproteinase and gamma-secretase.
• The nuclear localization of the gamma-secretase-generated fragment suggests a novel cell surface receptor signaling mechanism.
• This study provides the first experimental evidence for proteolytic regulation of protocadherin signaling.