PTK2 and myasthenia gravis: In addition, given that both activated FAK and Cdc42 are important for maintaining a polarized cytoskeleton and for forming membrane protrusions [45], the observed reduction of p-FAK(Ser910) and Cdc42 in PI-103-treated DK-MG cells might be responsible for the loss of cell polarity and inability to form lamellipodia, resulting in an overall inhibition of DK-MG cell migration (Figure 5C).