Protein Kinase A Subunit α Catalytic and A Kinase Anchoring Protein 79 in Human Placental Mitochondria

Maggie Pui Chi Ma

doi:10.2174/1874091x01206010023

Abstract

Components of protein phosphorylation signalling systems have been discovered in mitochondria and it has been proposed that these molecules modulate processes including oxidative phosphorylation, apoptosis and steroidogenesis. We used electrophoresis and Western blots probed with specific antibodies to protein kinase A α catalytic subunit (PKAα Cat) and A kinase anchoring protein of approximately 79 kDa molecular weight (AKAP79) to demonstrate the presence of these two proteins in human placental mitochondria. Heavy mitochondria characteristic of cytotrophoblast were separated from light mitochondria characteristic of syncytiotrophoblast by centrifugation. PKAα Cat and AKAP79 were present in both heavy and light mitochondria with no significant difference in concentration. Sucrose density gradient separation of submitochondrial fractions indicated PKAα Cat is located predominantly in the outer membrane whereas AKAP79 is present mainly in the contact site fractions. These data indicate that PKAα Cat is present in the cytoplasm, nucleus and mitochondria of placental cells. AKAP79 is also present in human placental mitochondria but there may be anchoring proteins other than AKAP79 responsible for fixing PKA to the outer membrane. PKA may play roles in mitochondrial protein phosphorylation systems in both cytotrophoblast and syncytiotrophoblast.

Highlights

It has been known for some time that protein phosphorylation by protein kinases is an important component of cellular signalling systems that are located in the plasma membrane, nucleus and cytoplasm [1]
There are several forms of A kinase anchoring proteins (AKAPs) that have been found in tissues and species other than placenta and human
PKAα Cat expression in Human Placental Tissue When Western blots of nuclei, microsomes and mitochondria were probed with the PKAα Cat antibody they all displayed a major band of immunoreactivity at approximately 44 kDa (Fig. 2)

Summary

Introduction

It has been known for some time that protein phosphorylation by protein kinases is an important component of cellular signalling systems that are located in the plasma membrane, nucleus and cytoplasm [1]. In many tissues it is known that protein kinases phosphorylate and activate key proteins such as receptors, enzymes and ion channels and these can in turn affect cellular functions such as metabolism, differentiation and endocrine functions [1, 2]. One of the most common protein kinases, cAMP-dependent protein kinase (PKA) can migrate to many areas of the cell and is often held in a precise cellular location by A kinase anchoring proteins (AKAPs) [7]. There are several forms of AKAP (often differentiated by a suffix corresponding to their molecular weight) that have been found in tissues and species other than placenta and human. The only form of AKAP found in human reproductive tissue prior to this investigation was AKAP79 which, was shown to be present in the cytoplasm of human

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Conclusion