Boudeau Jérôme, Baas Annette F, Deak Maria, Morrice Nick A, Kieloch Agnieszka, Schutkowski Mike, Prescott Alan R, Clevers Hans C, Alessi Dario R
MRC Protein Phosphorylation Unit, School of Life Sciences, MSI/WTB Complex, University of Dundee, Dow Street, Dundee DD1 5EH, UK.
EMBO J. 2003 Oct 1;22(19):5102-14. doi: 10.1093/emboj/cdg490.
Mutations in the LKB1 protein kinase result in the inherited Peutz Jeghers cancer syndrome. LKB1 has been implicated in regulating cell proliferation and polarity although little is known about how this enzyme is regulated. We recently showed that LKB1 is activated through its interaction with STRADalpha, a catalytically deficient pseudokinase. Here we show that endogenous LKB1-STRADalpha complex is associated with a protein of unknown function, termed MO25alpha, through the interaction of MO25alpha with the last three residues of STRADalpha. MO25alpha and STRADalpha anchor LKB1 in the cytoplasm, excluding it from the nucleus. Moreover, MO25alpha enhances the formation of the LKB1-STRADalpha complex in vivo, stimulating the catalytic activity of LKB1 approximately 10-fold. We demonstrate that the related STRADbeta and MO25beta isoforms are also able to stabilize LKB1 in an active complex and that it is possible to isolate complexes of LKB1 bound to STRAD and MO25 isoforms, in which the subunits are present in equimolar amounts. Our results indicate that MO25 may function as a scaffolding component of the LKB1-STRAD complex and plays a crucial role in regulating LKB1 activity and cellular localization.
LKB1蛋白激酶的突变会导致遗传性黑斑息肉综合征。LKB1与细胞增殖和极性调节有关，尽管人们对这种酶的调节方式知之甚少。我们最近发现，LKB1通过与STRADα相互作用而被激活，STRADα是一种缺乏催化活性的假激酶。在此我们表明，内源性LKB1-STRADα复合物通过MO25α与STRADα最后三个残基的相互作用，与一种功能未知的蛋白质MO25α相关联。MO25α和STRADα将LKB1锚定在细胞质中，使其无法进入细胞核。此外，MO25α在体内增强了LKB1-STRADα复合物的形成，将LKB1的催化活性提高了约10倍。我们证明，相关的STRADβ和MO25β亚型也能够在活性复合物中稳定LKB1，并且有可能分离出LKB1与STRAD和MO25亚型结合的复合物，其中各亚基以等摩尔量存在。我们的结果表明，MO25可能作为LKB1-STRAD复合物的支架成分，在调节LKB1活性和细胞定位中起关键作用。
