TNK2 and embryonal carcinoma: Specifically, while both CDC42 proteins are equally capable of binding to a downstream signaling target, Activated CDC42-associated Kinase (ACK), only CDC42b works together with ACK to promote the ubiquitination and degradation of mTOR, which leads to the downregulation of PAX6 and the promotion of neurogenesis in P19 embryonal carcinoma, as well as in E14 mouse embryonic stem cells (12).