On the Physiological Importance of Endoproteolysis of CAAX Proteins: HEART-SPECIFIC RCE1 KNOCKOUT MICE DEVELOP A LETHAL CARDIOMYOPATHY

Martin O Bergo,Hsiao D Lieu,Bryant J Gavino,Patricia Ambroziak,James C Otto,Patrick J Casey,Quinn M Walker,Stephen G Young

doi:10.1074/jbc.m310081200

Abstract

Proteins terminating with a CAAX motif, such as the Ras proteins and the nuclear lamins, undergo post-translational modification of a C-terminal cysteine with an isoprenyl lipid via a process called protein prenylation. After prenylation, the last three residues of CAAX proteins are clipped off by Rce1, an integral membrane endoprotease of the endoplasmic reticulum. Prenylation is crucial to the function of many CAAX proteins, but the physiologic significance of endoproteolytic processing has remained obscure. To address this issue, we used Cre/loxP recombination techniques to create mice lacking Rce1 in the heart, an organ where Rce1 is expressed at particularly high levels. The hearts from heart-specific Rce1 knockout mice manifested reduced levels of both the Rce1 mRNA and CAAX endoprotease activity, and the hearts manifested an accumulation of CAAX protein substrates. The heart-specific Rce1 knockout mice initially appeared healthy but died starting at 3-5 months of age. By 10 months of age, approximately 70% of the mice had died. Pathological studies revealed that the heart-specific Rce1 knockout mice had a dilated cardiomyopathy. By contrast, liver-specific Rce1 knockout mice appeared healthy, had normal transaminase levels, and had normal liver histology. These studies indicate that the endoproteolytic processing of CAAX proteins is essential for cardiac function but is less important for the liver.

Highlights

Proteins terminating with a CAAX motif, such as the Ras proteins and the nuclear lamins, undergo posttranslational modification of a C-terminal cysteine with an isoprenyl lipid via a process called protein prenylation
The fact that most do not survive postnatally indicates that CAAX protein endoproteolysis is somehow important; the survival of some Ras-converting enzyme 1 (Rce1)-deficient mice for a few weeks after birth indicates that the endoproteolytic processing is not nearly as important as prenylation for the vitality of mammalian cells and tissues
This study indicates that CAAX endoproteolysis is vitally important in the myocardium, as the absence of Rce1 in the heart caused a lethal-dilated cardiomyopathy

Summary

On the Physiological Importance of Endoproteolysis of CAAX Proteins

Liver-specific Rce knockout mice appeared healthy, had normal transaminase levels, and had normal liver histology These studies indicate that the endoproteolytic processing of CAAX proteins is essential for cardiac function but is less important for the liver. The fact that most do not survive postnatally indicates that CAAX protein endoproteolysis is somehow important; the survival of some Rce1-deficient mice for a few weeks after birth indicates that the endoproteolytic processing is not nearly as important as prenylation for the vitality of mammalian cells and tissues. We sought to assess the physiologic importance of the endoproteolytic processing of prenylated CAAX proteins To address this issue, we created mice lacking. This study indicates that CAAX endoproteolysis is vitally important in the myocardium, as the absence of Rce in the heart caused a lethal-dilated cardiomyopathy

EXPERIMENTAL PROCEDURES

RESULTS

DISCUSSION