Regulation by ERK1/2 of Novel Substrates, Kinesins KIF2A and KIF2C
The kinesin-like protein KIF2A is a microtubule-associated motor protein thatauses microtubule depolymerization by inducing a conformational change in tubulin. The depolymerase function of KIF2A is utilized in mitotic cells as it is required to establish proper, bipolar spindles. Studies in KIF2A knockout mice revealed KIF2A function in regulation of interphase microtubules as KIF2A-/- neurons exhibit abnormal axon branching. Though protein kinases are known to regulate the mitotic function of KIF2A, how KIF2A is regulated in interphase cells has not been studied. In a yeast-two hybrid screen, designed to preferentially uncover interactors of the active form of ERK2, we identified KIF2A. We find that, human KIF2A can be v phosphorylated in vitro by pERK1/2 and that the kinases interact with KIF2A in cells. Through phosphorylation prediction tools and mutagenesis we identified threonine 78 (T78) as a major pERK2 phosphorylation site on KIF2A. Inhibition of ERK1/2 prevents KIF2A from localizing at the leading edge of cells. Additionally, knockdown of KIF2A phenocopies the effect of inhibiting ERK1/2 on microtubules; both treatments result in elongated microtubules. These data suggest that ERK1/2 may regulate KIF2A localization which in turn may be important for KIF2A function in depolymerizing microtubules. The close relative, KIF2C can also bind to and be phosphorylated by pERK1/2 in vitro, but the functional significance of this event remains unknown. In a laboratory generated non-small cell lung cancer (NSCLC) in which oncogenic K-RasG12V has been overexpressed and the tumor suppressor p53 has been knocked down, we found an increase in expression of KIF2A and KIF2C. This increase could be suppressed by inhibiton of the effector pathway RAS-RAF-MEK1 but not the PI3K pathway. As it is accepted that cancer cells have more dynamic microtubules that give them a migratory advantage, we hypothesized that upregulation of KIF2A and KIF2C also promote migration. Indeed, knockdown of KIF2A and KIF2C resulted in reduced migration in cancer cell lines. Microarray studies that had been performed on lung cancer lines revealed upregulation of KIF2A and KIF2C in cancers, suggesting that these proteins may be significant factors in the development of lung cancer. Finally, KIF2A and KIF2C regulate lysosomal dynamics. This regulation has an impact on signaling, particularly for mTORC1 which requires lysosomal localization for its activity.