Functional Analysis of LKB1/STK11 Mutants and Two Aberrant Isoforms Found in Peutz-Jeghers Syndrome Patients

Hum Mutat. 2003 Feb;21(2):172. doi: 10.1002/humu.9112.

Abstract

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cell Division / genetics
  • Cell Division / physiology
  • Cell Line
  • Cell Nucleus / chemistry
  • Cell Nucleus / enzymology
  • Cytoplasm / chemistry
  • Cytoplasm / enzymology
  • Enzyme Activation / genetics
  • Enzyme Activation / physiology
  • Glutathione Transferase / biosynthesis
  • Glutathione Transferase / genetics
  • HeLa Cells
  • Humans
  • Immunoblotting
  • Isoenzymes / genetics
  • Isoenzymes / immunology
  • Isoenzymes / physiology
  • Kidney
  • Melanoma / chemistry
  • Melanoma / enzymology
  • Melanoma / metabolism
  • Melanoma / pathology
  • Mutation / genetics
  • Mutation / physiology*
  • Peutz-Jeghers Syndrome / enzymology*
  • Peutz-Jeghers Syndrome / genetics
  • Peutz-Jeghers Syndrome / physiopathology*
  • Phosphorylation
  • Protein-Serine-Threonine Kinases / biosynthesis
  • Protein-Serine-Threonine Kinases / deficiency
  • Protein-Serine-Threonine Kinases / genetics
  • Protein-Serine-Threonine Kinases / immunology
  • Protein-Serine-Threonine Kinases / physiology*
  • Recombinant Fusion Proteins / biosynthesis
  • Recombinant Fusion Proteins / genetics
  • Threonine / metabolism
  • Tumor Cells, Cultured
  • Tumor Suppressor Protein p53 / metabolism

Substances

  • Isoenzymes
  • Recombinant Fusion Proteins
  • Tumor Suppressor Protein p53
  • Threonine
  • Glutathione Transferase
  • STK11 protein, human
  • Protein-Serine-Threonine Kinases