Peutz-Jeghers Syndrome and LKB1/STK11 Kathryn Satterfield

THE DISEASE Intestinal polyposis Increased risk of cancer in the gastrointestinal tract and reproductive organs Pigmented spots on the skin. Autosomal Dominant Peutz- Jeghers Syndrome is a rare, autosomal dominantly inherited intestinal polyposis syndrome that is associated with a significantly increased risk of several types of cancer, particularly gastrointestinal and reproductive organs, but MOSTLY in the small intestine. Also characterized by lesions of the skin…… The lifetime risk of developing cancer for individuals with PJS is estimated to be 93% and the mean age of cancer diagnosis is 43 years. It was described in a Dutch family by Peutz in 1921, and later in 1949 by Jeghers. Individuals with PJS are predisposed to development of hamartomatous polyps and carcinomas of the small intestine. This is similar to Cowden's disease and Juvenile polyposis, which we previously discussed that also result in hamartomatous polyps in the colon in Cowden's disease, and in various organs in Juvenile polyposis. Small intestine rarely develops cancer even though it is a highly proliferative tissue. This is remarkably different from colorectal cancer. FUN FACT: 5,300 new cases of cancer of the small intestine were anticipated in the US in 2002, and 148,000 cases of colorectal cancer were predicted. Boudeau, J et al. LKB1, a protein kinase regulating cell proliferation and polarity. FEBS Letters 2003. 546:159-165. Yoo L, et al. LKB1- A Master Tumour Suppresor of the Small Intestine and Beyond. Nature Reviews. 2002. 7:529- 535.

THE DISEASE Predisposed to development of hamartomatous polyps of the small intestine. Lifetime cancer risk: 93%. Boudeau, J et al. LKB1, a protein kinase regulating cell proliferation and polarity. FEBS Letters 2003. 546:159-165. Yoo L, et al. LKB1- A Master Tumour Suppresor of the Small Intestine and Beyond. Nature Reviews. 2002. 7:529- 535.

LKB1 Gene In 1997 Peutz-Jeghers syndrome was linked to loss-of-function mutations both alleles of LKB1. Thus LKB1 might suppress tumorigenesis in the intestine Boudeau, J et al. LKB1, a protein kinase regulating cell proliferation and polarity. FEBS Letters 2003. 546:159-165. Yoo L, et al. LKB1- A Master Tumour Suppresor of the Small Intestine and Beyond. Nature Reviews. 2002. 7:529- 535.

LKB1 PROTEIN STRUCTURE LKB1 encodes a serine threonine kinase Homologs in mice, Drosophila, and C. elegans, but NOT in yeast. LKB1 is located both in the nucleus and the cytoplasm. LKB1 mutations in PJS patients are found in the Kinase domain and the C-terminal regulatory domain. Boudeau, J et al. LKB1, a protein kinase regulating cell proliferation and polarity. FEBS Letters 2003. 546:159-165. Yoo L, et al. LKB1- A Master Tumour Suppresor of the Small Intestine and Beyond. Nature Reviews. 2002. 7:529- 535.

LKB1 REGULATION Not much is known about its normal function however, two post-translational modifications have been identified. LKB1 activity is believed to be regulated by phosphorylation. Multiple phosphorylation sites have been identified how. However, as no endogenous substrates of LKB1 have been identified, the effects of these phosphorylation sites are unknown. Name specific phosphorylation sites Also significant, is a second post-translational modification. The carboxy terminus of LKB1 contains a consensus sequence CAAX box for prenylation. This is a modification that directs the protein to the plasma membrane. However, the consequence and function of this modification is unknown as well. name specific spot Experiments show that LKB1 is located both in the nucleus and the cytoplasm. High levels of expression are found in the pancreas, liver, skeletal muscle as well as the testis. Picture of adult with organs colored In general, expression of LKB1 is higher during embryonic development in all the adult tissues as well as in the small intestine and stomach. Has multiple phosphorylation sites- Regulated by phosphorylation?? The C-terminus contains a CAAX box for prenylation. Boudeau, J et al. LKB1, a protein kinase regulating cell proliferation and polarity. FEBS Letters 2003. 546:159-165. Yoo L, et al. LKB1- A Master Tumour Suppresor of the Small Intestine and Beyond. Nature Reviews. 2002. 7:529- 535.

STRAD An LKB1-specific adaptor protein and substrate. Translocates LKB1 from the nucleus to the cytoplasm. In some mutant cell lines LKB1 translocation does not occur. Baas AF, et al. Activation of the tumour suppressor kinase LKB1 by the STE20-like pseudokinase STRAD. EMBO J. 2003. Jun 16;22(12):3062-72.

POSSIBLE FUNCTIONS OF LKB1 Interactions with p21 Interactions with p53 Interactions with wnt pathway Role in cell polarization Interactions with PTEN Possible regulation of ERK and COX-2 Tiainen M. et al. Growth Supprestion by Lkb1 is mediated by a G1 cell cycle arrest. 1999 Aug 3; PNAS 96 (16: 9248-51. Karuman P. et al. The Peutz-Jegher gene product LKB1 is a mediator of p53-dependent cell death. Mol Cell. 2001 Jun;7(6): 1307-19. Spicer J, et al. Regulation of the Wnt signalling component PAR1A by the Peutz-Jeghers syndrom kinase LKB1. Oncogene. 2003 Jul 24;22(30):2752-6. Ossipova O et al. LKB2 (XEEK1) regulates Wnt signalling invertebrate development. Nat Cell Biol. 2003 Oct; 5(10):889-94. Smith D et al. LIP2, a cytoplasmic protein functionally linked to the Peutz-Jeghers syndrom kinase LKB1. Human Molecular Genetics, 2001, 10(25): 2869-77. Takeda H et al. Simultaneous expression of COX-2 and mPGES-1 in mouse gastrointestinal hamartomas. British Journal of Cancer. 2004 90: 701-704.

Death occurs at mid-gestation. MOUSE KNOCKOUTS LKB1 -/- mice are embryonic lethal. Death occurs at mid-gestation. Knockout leads to abnormal development of the neural tube, heart and placenta. LKB1+/- mice are useful for studying LKB1’s role in tumorigenesis. Ylikorkala A. et al. Vascular abnormalities and deregulations of VEGF in LKB1-deficient mice. Science. 2001 Aug 17; 293(5533): 1323-6.

Drosophila and C. elegans Kinesin label in fly oocytes A) WT LKB1 B) LKB1 mutant LKB1 is necessary for the formation of the A-P axis in c. elegans and Drosophila. LKB1 plays a role in apical-basal epithelial polarity in these models. Loss of cell polarity may contribute to tumor formation in PJS. A B Highlighted material is Kinesin B, expected to concentrate at posterior of the oocyte in WT, right is posterior Martin SG et al. A role for Drosophila LKB1 in anterior-posterior axis formation and epithelial polarity. Nature. 2003 Jan 23;421(6921):379.

Recent Studies on LKB1 in cells Created cell line in which STRAD (an LKB1 activator) is inducible. Activation of LKB1 resulted in complete polarization in intestinal epithelial cell lines! Baas AF, et al. Complete Polarization of Single Intestinal Epithelial Cells upon Activation of LKB1 by STRAD. Cell. 2004 Feb 6; 116:457-66.

Recent Studies on LKB1 in cells Baas AF, et al. Complete Polarization of Single Intestinal Epithelial Cells upon Activation of LKB1 by STRAD. Cell. 2004 Feb 6; 116:457-66.

SUMMARY Not much is known about the endogenous function of LKB1 or how the mutations identified play a role in creating cancer. The most recent research implicates that LKB1 may play a role in cell polarity. Research continues in the investigation of the endogenous role of LKB1 in all the areas discussed as well as the role of LKB1 in tumorigenesis in heterozygous mice.