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Regulation of Lynch syndrome-related DNA mismatch repair heterodimer MutLalpha
by phosphorylation?
Angela Brieger, Sandra Passmann, Stefan Zeuzem and Jörg Trojan
Medical Clinic I, Biomedical Research Laboratory, Goethe-University, Frankfurt a.M.,
Germany
Lynch syndrome, a hereditary disease associated with many different tumor types, is caused
by mutations in DNA mismatch repair (MMR)-genes. 50% of these mutations are detected in
the MLH1 protein. The heterodimer MutLalpha, which is formed by MLH1 and PMS2,
coordinates a series of key events in the MMR mechanism. In addition to MMR, MutLalpha
is involved in many other cellular processes as the regulation of cell cycle checkpoints and
apoptosis most likely signaling DNA damage to downstream pathways. A sophisticated
regulation of the different MutLalpha functions might be important as well as reasonable. In
order to focus on MutLalpha modulation, we analyzed MLH1 and PMS2 for phosphorylation
sites using different computational systems and detected multiple potential loci and
corresponding kinases for both genes. Using phospho-specific purification columns we were
able to isolate unphosphorylated and phosphorylated MLH1. In addition to this, Westernblot
analysis of 2-D gels resolved MLH1 into several different distinct forms detected in lysates
from HEK293 cells. Furthermore, we detected phosphorylation of purified MLH1 by
PKCdelta, one of the computer-supported most probable MutLalpha kinases. Ongoing
projects are directed towards the understanding how phosphorylation might be capable to
switch MutLalpha function between MMR and DNA damage signaling.
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