A CRM1-dependent nuclear export pathway is involved in the regulation of MutLα subcellular localization.
MutLα plays an essential role in DNA mismatch repair (MMR) and is additionally involved in other cellular mechanisms such as the regulation of cell cycle checkpoints and apoptosis. Therefore, not only germline MMR gene defects but also the subcellular localization of MutLα might be of importance for the development of Lynch syndrome. Recently, we showed that MutLα contains functional nuclear import sequences and is most frequently localized in the nucleus. Here, we demonstrate that MutLα can move bidirectionally towards the nuclear membrane. Using MutLα transfected HEK293T cells we observed a significant shift of MLH1 and PMS2 from the nucleus to the cytoplasm after irradiation or cisplatin treatment. We analyzed both proteins for potential nuclear export sequences (NES) and identified one functional Rev-type NES (⁵⁷⁸LFDLAMLAL) in the C-terminal part of MLH1 that facilitates export via the CRM1/exportin pathway. Moreover, an MLH1-NES mutation detected in a patient with Lynch syndrome showed normal MMR activity but led to significantly impaired cytoplasmic transport after actinomycin D treatment. These results indicate that MutLα is able to shuttle from the nucleus to the cytoplasm, probably signaling DNA damages to downstream pathways. In conclusion, not only a defective MMR but also impaired nucleo-cytoplasmic shuttling might result in the onset of Lynch syndrome.
Medical Clinic I, Biomedical Research Laboratory, Goethe-University, Frankfurt a.M., Germany. a.brieger@em.uni-frankfurt.de
Angela
A
Brieger
Ronja
R
Adam
Sandra
S
Passmann
Guido
G
Plotz
Stefan
S
Zeuzem
Jörg
J
Trojan
D021581:Active Transport, Cell Nucleus / Q000235:genetics; D048868:Adaptor Proteins, Signal Transducing / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D000251:Adenosine Triphosphatases / Q000378:metabolism; D000595:Amino Acid Sequence; D002467:Cell Nucleus / Q000378:metabolism*; D002945:Cisplatin / Q000494:pharmacology; D004249:DNA Damage / Q000235:genetics; D053843:DNA Mismatch Repair / Q000235:genetics; D045643:DNA Repair Enzymes / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism; D045325:HCT116 Cells; D057809:HEK293 Cells; D006801:Humans; D042541:Intracellular Space / Q000378:metabolism*; D028884:Karyopherins / Q000378:metabolism*; D000070976:Mismatch Repair Endonuclease PMS2; D000070957:MutL Protein Homolog 1; D000070956:MutL Proteins; D009154:Mutation / Q000235:genetics; D049790:Nuclear Export Signals / Q000235:genetics; D009687:Nuclear Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D021381:Protein Transport / Q000187:drug effects / Q000528:radiation effects; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism*; D000097606:Exportin 1 Protein
D048868:Adaptor Proteins, Signal Transducing; D000251:Adenosine Triphosphatases; D002945:Cisplatin; D045643:DNA Repair Enzymes; D004268:DNA-Binding Proteins; D028884:Karyopherins; D000070976:Mismatch Repair Endonuclease PMS2; D000070957:MutL Protein Homolog 1; D000070956:MutL Proteins; D049790:Nuclear Export Signals; D009687:Nuclear Proteins; D011838:Radiation-Sensitizing Agents; D018160:Receptors, Cytoplasmic and Nuclear; D000097606:Exportin 1 Protein; C501486:MLH1 protein, human; C500929:MutLalpha protein, human; C094934:PMS2 protein, human