Microtubule association of EML proteins and the EML4-ALK variant 3 oncoprotein require an N-terminal trimerization domain

Proteins of the echinoderm microtubule associated protein-like (EML) family contribute to formation of the mitotic spindle and interphase microtubule (MT) network. EML1-4 consist of WD40 repeats and an N-terminal region containing a putative coiled-coil. Recurrent gene rearrangements in non-small cell lung cancer (NSCLC) fuse EML4 to anaplastic lymphoma kinase (ALK) causing expression of several oncogenic fusion variants. The fusions have constitutive ALK activity due to self-association through the EML4 coiled-coil. We have determined crystal structures of the coiled-coils from EML2 and EML4, which describe the structural basis of both EML self-association and oncogenic EML4-ALK activation. The structures reveal a trimeric oligomerization state directed by a conserved pattern of hydrophobic residues and salt bridges. We show that the trimerization domain (TD) of EML1 is necessary and sufficient for self-association. The TD is also essential for MT binding, however this property requires an adjacent basic region. These observations prompted us to investigate MT association of EML4-ALK and EML1-ABL1 fusions in which variable portions of the EML component are present. Uniquely, EML4-ALK variant 3, which includes the TD and basic region of EML4 but none of the WD40 repeats, was localized to MTs, both when expressed recombinantly and in a patient-derived NSCLC cell line (H2228). This raises the question of whether the mislocalization of ALK activity to MTs might influence downstr...
Source: BJ Disease - Category: Biochemistry Authors: Tags: BJ Biomolecules Source Type: research