A truncated isoform of pyroglutamyl aminopeptidase II produced by exon extension has dominant-negative activity

Area of Science:

• Biochemistry
• Molecular Biology
• Enzymology

Background:

• Thyrotropin-releasing hormone (TRH) is inactivated extracellularly by pyroglutamyl aminopeptidase II (PPII), a zinc metallopeptidase.
• The functional role of diverse PPII RNA species remains unclear.

Purpose of the Study:

• To investigate the functional significance of alternative RNA processing in PPII expression.
• To characterize a novel, shorter PPII isoform (PPII*) and its regulatory mechanism.

Main Methods:

• Detection of alternative RNA splicing in rat tissues using molecular techniques.
• Expression of PPII and PPII* isoforms in cell lines (COS-7, C6 glioma).
• Assay of PPII enzymatic activity and analysis of protein-protein interactions (heterodimerization).

Main Results:

• An alternatively processed RNA species encoding a truncated PPII (PPII*) was identified in rat tissues.
• PPII* lacks C-terminal domains and exhibits no intrinsic PPII activity.
• Co-expression of PPII and PPII* led to a dose-dependent inhibition of PPII activity via PPII-PPII* heterodimer formation.

Conclusions:

• PPII* functions as a potent dominant-negative regulator of PPII activity.
• Heterodimerization is a likely mechanism for PPII* mediated inhibition.
• Alternative splicing producing shortened isoforms may represent a novel regulatory strategy for M1 metallopeptidases.