Living cells are continuously exposed to a variety of signals from their micro- and macro- environment. Many signals are detected by receptors present on the cell surface, and signal transduction generally involves the movement – or translocation – of signaling proteins from one position to another within the cell.

As an example of a typical signal transduction pathway involving protein translocation, consider the signaling steps involved in the cellular response to a growth factor such as insulin:

For an animation of the key protein translocation in the PI3K pathway, click here.

1) Insulin binds to and activates its receptor. Upon activation, the receptor recruits adaptor proteins and activates intracellular signaling molecules such as PI3 kinase.

2) Activated PI3 kinase increases the plasma membrane concentration of the lipid phosphatidylinositol 3,4,5-triphosphate (PIP3).

3) PIP3 in the plasma membrane provides docking sites for protein kinases including Akt/PKB and PDK1; Akt is activated by PDK1 only when both are docked at the membrane. This translocation step is an absolute requirement for Akt activation

Translocation of Akt: view movie

4) Once activated by PDK1 at the plasma membrane, Akt is free to diffuse back into the cell, where it can phosphorylate substrates such as isoforms of the transcription factor Forkhead (FKHR, FOXOA1).

5) Hypo-phosphorylated FKHR normally resides in the nucleus, where it modulates genes involved in cell cycle arrest and apoptosis. However, once phosphorylated by Akt, FKHR translocates to the cytoplasm, where it can no longer modulate target genes.

Translocation of Forkhead: view movie

Translocation and Disease
Altered signalling responses are often key distinguishing features between cells in normal and diseased tissues. The therapeutic relevance of translocation is illustrated by considering the insulin pathway: binding of insulin to cell surface receptors modulates the transcription of genes involved in cellular growth and survival via a sequential cascade of protein translocation events, as illustrated above.

Measurement of translocation is a readout for signalling in a given pathway, but could also be considered as an approach to modulate signaling for therapeutic purposes.

BioImage Provides Redistribution^® Assays
BioImage has developed a patented high throughput assay technology, termed Redistribution^®, that is uniquely focused on quantifying protein translocation in living cells, and on the discovery of compounds that directly or indirectly modulate protein translocation.

For more information on our assays in a number of therapeutically relevant signalling pathways, please see our Products & Services document.