Cytoplasmic LEK1 is a regulator of microtubule function through its interaction with the LI51 pathway.

LIS1 and nuclear distribution gene E (NudE) are partner proteins in a conserved pathway regulating the function of dynein and microtubules. Here, we present data that cytoplasmic LEKI (cytLEKI), a large protein containing a spectrin repeat and multiple leucine zippers, is a component of this pathway through its direct inter- action with NudE, as determined by a yeast two-hybrid screen. We identified the binding domains in each molecule, and coimmuno-precipitation and colocalization studies confirmed the specificity of the interaction between cytLEKI and NudE. Confocal deconvolution analysis revealed that cytLEKI exhibits colocalization with endogenous NudE and with the known NudE binding partners, LISI and dynein. By localizing the NudE-binding domain of cytLEK1 to a small domain within the molecule, we were able to disrupt cytLEK1 function by using a dominant negative approach in addition to LEK1 knockdown and, thus, examine the role of the cytLEK1-NudE interaction in cells. Consistent with a defect in the LISI pathway, disruption of cytLEK1 function resulted in alteration of microtubule organization and cellular shape. The microtubule network of cells became tightly focused around the nucleus and resulted in a rounded cell shape. Additionally, cells exhibited a severe inability to repolymerize their microtubule networks after nocodazole challenge. Taken together, our studies revealed that cytLEK1 is essential for cellular functions regulated by the LISI pathway. [ABSTRACT FROM AUTHOR]