Tubulin-independent tau in Alzheimer's disease and cancer: implications for disease pathogenesis and treatment.

Microtubule-associated protein tau has long been known for its ability to promote microtubule assembly. A less known feature of tau is its existence as a non-microtubule associated protein. Here we review the interactions of tau with other proteins, some of which interact with the microtubule binding repeat region of tau. The tau interactions with Fyn and with Pin1 have attracted the most attention and both interactions have been thought to have a role in Alzheimer's disease. The fact that tau has unknown cellular functions is further evidenced by its involvement in cell cycle activated neurodegeneration. One possible route for additional investigations stems from the presence of tau in non-neuronal cells where its characteristics have been largely unknown, although there has been a correlation between tau levels and the response of some cancer cells to microtubule-targeting chemotherapy drugs. Our studies of prostate cancer cells indicate that these cells can provide a system with phosphorylated adult tau for functional studies. In fact, structural similarities exist between Alzheimer's disease tau and prostate cancer cell tau, raising the possibility that new tau functions uncovered in prostate cancer cells will have relevance to Alzheimer's disease.