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Teaser, summary, work performed and final results

Periodic Reporting for period 1 - Class II PI3K (Characterization of the signalling and physiological roles of the class II PI3Ks)

Teaser

Summary

This project deals with important regulators of fundamental processes inside mammalian cells, called phosphoinositide 3-kinases (abbreviated as PI3Ks). This family comprises 8 members, called isoforms, in mammals.

One function of PI3Ks is to transmit signals from the outside to the inside of cells, and make the cells respond in appropriate ways. This process is called signal transduction, and four members of the PI3K family, called the class I PI3K, have been shown to be essential for this. Another function is to remodel intracellular membranes in a process called vesicular trafficking, and this is what the other four PI3Ks (the class II and III isoforms) are believed to control. Vesicular traffic serves to exchange contents with the outside and in between different compartments of a cell, much like rooms within a house that have distinct functions. However, much less is known about those class II and III PI3Ks and how signal transduction and vesicular trafficking are interconnected.

An important scientific question is to clarify the functions of the different PI3K family members and understand how they work. Thus far, scientists have mainly studied the class I PI3Ks and discovered specialised functions of the different family members, both in healthy tissue and in cancer, inflammation and diabetes. Drugs against class I PI3Ks are currently being tested in clinical trials in human cancer and allergy. The class III PI3K has been shown to be important for the distribution and processing of materials taken up by cells, as well as for a process called self-eating that helps to keep the cell clean and organized.

To date, comparably little is known about the class II PI3Ks, especially about their physiological importance and whether they could be useful drug targets.

In this project, we have set out to explore novel functions of the class II PI3Ks that depend on their enzymatic activity and could hence indicate their potential as drug targets.

These studies are largely based on mice in which class II PI3Ks have been inactivated, an approach that has been shown to successfully model inactivation in a drug-like fashion (illustrated in the scheme below). The most common approach of genetic manipulation of model organisms, the so-called knock-out, entirely removes the targeted enzyme from the organism. The important difference to our approach is that the enzyme is still present, but will be inactive â€“ just as if a drug against this enzyme were being used.

Work performed

Genetic removal as well as inactivation of PI3K-C2Î±, one of the class II PI3Ks, is not tolerated during the embryonic development of mice. We have therefore devised and established a method for the inducible inactivation of this enzyme in post-natal stages. This approach has allowed us to obtain cellular model systems derived from these mice. Furthermore, it has enabled us to induce the inactivation of this enzyme in all tissues examined with an efficiency between 75 â€“ 100 % inactivation, with the sole exception of the brain. This has revealed that inactivation of PI3K-C2Î± in adult mice is surprisingly well tolerated, and mice remain viable up to one year after inactivation. However, inactivation of this PI3K causes mice to gain less weight compared to controls, indicative of substantial but not fatal physiological impact of PI3K-C2Î± inactivation.

Final results

This project has for the first time assessed the consequences of inactivation of a poorly understood class II PI3K family member in adult mice. Contrary to expectations, this has revealed that loss of the activity of this enzyme can be tolerated in adult mice. Regarding the potential future development of drugs targeting this PI3Ks, this is of major importance: such a drug would allow to specifically interfere with PI3K-C2Î±-dependent processes without causing serious or even fatal effects to normal physiology. We are currently exploring the nature of the condition caused by inactivation of PI3K-C2Î± in adult mice. This is expected to reveal the physiological importance of this isoform in adult organisms and to uncover potential indications for a therapeutic exploitation of our findings.