Specifically, protein kinase A and p21-activated kinases phosphorylate S518 residing on the tail domain, thereby inactivating the tumor-suppressive activity of neurofibromin 217–20, while the myosin phosphatase MYPT1-PP1δ activates its tumor suppressor function by dephosphorylating S51821. The gene discussed is PPP1CB; the disease is neoplasm.