UC Berkeley

The microtubule cytoskeleton is essential for regulation of cell morphology, trafficking within the cell and cell cycle progression. These diverse functions involve complex microtubule dynamics and the interaction of microtubule-associated proteins (MAPs), molecular motors, and various small ligands. Here we investigate three distinct aspects of microtubule activity: the interactions of microtubules with parkin and tau which may be involved in Parkinson's disease and Alzheimer's disease, respectively, and effects on microtubule stability in prostate cancer.

Autosomal Recessive Juvenile Parkinson's disease (ARJP) is a degenerative disorder of the central nervous system. Over 50% of ARJP cases result from mutations that occur within the PARK2 gene that encodes the protein parkin. Recent evidence has suggested that parkin binds to microtubules and can stabilize microtubules against depolymerization. Visualization of the parkin-tubulin complex would help us understand the mechanism of this interaction and provide insights on the role of parkin in the cell. Parkin was expressed, purified and used to decorate microtubules for cryo-electron microscopy. Fourier transforms of images suggest that parkin binds specifically to the tubulin dimer. Further cryo microscopy of the interaction of parkin with microtubules will help define the etiology of ARJP and may reveal novel targets of therapeutic intervention.

Hyperphosphorylation of the microtubule-associated protein tau results in a pathological form of the protein found in plaques of patients with Alzheimers disease. Our work has been focused on clarification of the two current models proposed for tau binding along the outside and the inside of the microtubule.

Microtubule networks are also clinically important as targets of many chemotherapeutic drugs. Prostate cancer is commonly treated with the microtubule-targeted drug paclitaxel (taxol). A previous report indicated that supplemental zinc sensitized prostate cancer cells to taxol-induced apoptosis, suggesting that increased zinc levels might affect taxol efficacy. We tested taxol's effect in two prostate cancer cell lines maintained under moderately zinc deficient conditions. Taxol-induced apoptosis was reduced in LNCaP cells from zinc-deficient conditions. The IC50 for paclitaxel-induced cell cycle arrest was higher in LNCaP cells. Extracellular zinc levels were thus shown to be an important factor in paclitaxel activity in a prostate cell cancer line.