Functional analysis of LKB1/STK11 mutants and two aberrant isoforms found in Peutz-Jeghers Syndrome patients.
Peutz-Jeghers Syndrome (PJS) is thought to be caused by mutations occurring in the widely expressed serine/threonine protein kinase named LKB1/STK11. Recent work has led to the identification of four mutants (R304W, I177N, K175-D176del, L263fsX286) and two novel aberrant LKB1/STK11 cDNA isoforms (r291-464del, r485-1283del) in a group of PJS Italian patients. Three of the four mutations only change 1 or 2 amino acids in the LKB1/STK11 catalytic domain. Here we demonstrate that all six LKB1/STK11 variants analysed are completely inactive in vitro as they were unable to autophosphorylate at Thr336, the major LKB1/STK11 autophosphorylation site, and to phosphorylate the p53 tumour suppressor protein. We also show that 5 out of the 6 variants are entirely localised in the nucleus in contrast to the wild type LKB1/STK11, which is detected in both the nucleus and cytoplasm. Finally we demonstrate that all 6 LKB1/STK11 variants, in contrast to wild type LKB1/STK11, are unable to suppress the growth of melanoma G361 cells. Taken together, these results demonstrate that the LKB1 mutations investigated in this study lead to the loss of serine/threonine kinase activity and are therefore likely to be the primary cause of PJS development in the patients that they were isolated from.
Boudeau
J
J
MRC Protein Phosphorylation Unit, MSI/WTB complex, University of Dundee, Dow Street, Dundee DD1 5EH, Scotland.
Kieloch
A
A
Alessi
D R
DR
Stella
A
A
Guanti
G
G
Resta
N
N
D000091162:AMP-Activated Protein Kinase Kinases; D002455:Cell Division / Q000235:genetics / Q000502:physiology; D002460:Cell Line; D002467:Cell Nucleus / Q000737:chemistry / Q000201:enzymology; D003593:Cytoplasm / Q000737:chemistry / Q000201:enzymology; D004789:Enzyme Activation / Q000235:genetics / Q000502:physiology; D005982:Glutathione Transferase / Q000096:biosynthesis / Q000235:genetics; D006367:HeLa Cells; D006801:Humans; D015151:Immunoblotting; D007527:Isoenzymes / Q000235:genetics / Q000276:immunology / Q000502:physiology; D007668:Kidney; D008545:Melanoma / Q000737:chemistry / Q000201:enzymology / Q000378:metabolism / Q000473:pathology; D009154:Mutation / Q000235:genetics / Q000502:physiology*; D010580:Peutz-Jeghers Syndrome / Q000201:enzymology* / Q000235:genetics / Q000503:physiopathology*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000096:biosynthesis / Q000172:deficiency / Q000235:genetics / Q000276:immunology / Q000502:physiology*; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis / Q000235:genetics; D013912:Threonine / Q000378:metabolism; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism
D007527:Isoenzymes; D011993:Recombinant Fusion Proteins; D016159:Tumor Suppressor Protein p53; D013912:Threonine; D005982:Glutathione Transferase; D017346:Protein Serine-Threonine Kinases; C109790:STK11 protein, human; D000091162:AMP-Activated Protein Kinase Kinases