Is there a mitochondrial signaling complex facilitating cholesterol import?

Cholesterol transport into mitochondria is the rate-determining and hormone-sensitive step in steroid biosynthesis. During the last few years two proteins were shown to be critical for this process: the mitochondrial translocator protein, previously known as peripheral-type benzodiazepine receptor, and the steroidogenic acute regulatory protein. In this manuscript we review evidence suggesting that these two proteins functionally interact to facilitate cholesterol transport and may be part of a larger multimeric mitochondrial complex of proteins assembled to facilitate the hormone-induced cholesterol transfer into mitochondria. This complex might include proteins such as the mitochondrial voltage-dependent anion channel, the translocator protein-associated protein PAP7 which also functions as an A kinase anchor protein that binds and brings into the complex the regulatory subunit Ialpha of the cAMP-dependent protein kinase.