The role of LKB1 in T-Lymphocytes. (360G-Wellcome-078378_B_05_Z)

The serine/threonine kinase LKB1 was first identified as a tumour suppressor from genetic linkage analysis of mutations in Peutz-Jeghers Syndrome. LKB1 has now been identified as an essential multifunctional kinase, with LKB1 null mice dying midgestatin. We have previously demonstrated that LKB1 has an essential role in T-lymphocytes via the generation of mice with a conditional LKB1 gene deletion in T-cell progenitors in the thymus. Thesemice have effectively no peripheral T-lymphocytes, with the mice exhibiting a block in theymocytic development at the pre-T (double negative 4 - DN4) stage. Recently we have shown that these DN4 cells will proliferate, but not differentiate, when grown on OP9-DL1 stromal cells, allowing the generation of large numbers of cells for analysis. The binding partners and localisation of LKB1 in T-lymphocytes have yet to be defined, however affinity purification studies in other cell types suggest that the localisation of endogenous LKB1 is dependent on attached proteins. It has been observed that LKB1 localises to the nucleus unless complexed with the pseudokinase STE20-related adaptor (STRAD) and mouse protein 25 (MO25), in which case the complex localises to the cytoplasm. Additional binding partners for LKB1 have also been reported. Importantly, the presence of STRAD and MO25 increases the catalytic activity of LKB1 about 10 fold. The aim of this project is therefore to investigate the role of LKB1 in lymphocytes via the study of LKB1 localisation, characterisation of existing LKB1 null DN4 thymocytes and the generation of lymphocytes with tamoxifen-inducible LKB1 gene deletions. These cells will be utilised to investigate the role of LKB1 in the polarisation of lymphocytes during both migration and CTL degranulation.