The immunophilin FKBP52 specifically binds to tubulin and prevents microtubule formation.

The FK506 binding protein FKBP52 belongs to the large family of immunophilins and is known as a steroid receptor-associated protein. Previous data suggest that FKBP52 is associated with the motor protein dynein and with the cytoskeleton during mitosis. Here we demonstrate a specific and direct interaction between FKBP52 and tubulin. The region of FKBP52 located between aa 267 and 400, which includes the tetratricopeptide repeat domain, is required for tubulin binding. We provide evidence that FKBP52 prevents tubulin polymerization and that an 84 residue sequence located in the C-terminal part of the molecule (aa 375-458) is necessary and sufficient for its microtubule depolymerization activity. In colocalization experiments in PC12 cells, FKBP52 is associated with tubulin in motile cellular compartments. Furthermore, we suggest that, by using siRNA, a decrease of FKBP52 expression in PC12 cells may lead to differentiated cell phenotype characterized by neurite extensions. Collectively, our data define an unexpected property of FKBP52 as a novel regulator of microtubule dynamics. The possible role of microtubule formation and tubulin binding of other immunophilins such as FKBP12 and FKBP51 is discussed.

Microtubule-associated protein 2 (MAP2) is a neurosteroid receptor.

The neurosteroid pregnenolone (PREG) and its chemically synthesized analog 3beta-methoxypregnenolone (MePREG) bind to microtubule-associated protein 2 (MAP2) and stimulate the polymerization of microtubules. PREG, MePREG, and progesterone (PROG; the physiological immediate metabolite of PREG) significantly enhance neurite outgrowth of nerve growth factor-pretreated PC12 cells. However, PROG, although it binds to MAP2, does not increase the immunostaining of MAP2, contrary to PREG and MePREG. Nocodazole, a microtubule-disrupting agent, induces a major retraction of neurites in control cultures, but pretreatment with PREG/MePREG is protective. Decreasing MAP2 expression by RNA interference does not modify PROG action, but it prevents the stimulatory effects of PREG and MePREG on neurite extension, showing that MAP2 is their specific receptor.

MAPREG: toward a novel approach of neuroprotection and treatment of Alzheimer's disease.

MAPREG (microtubule-associated protein/neurosteroidal pregnenolone) is a start-up company that was created in October 2000. Its acronym recalls the basic discovery (Murakami et al., 2000) from which drug(s) will hopefully be developed that are useful for neuroprotection and repair in conditions such as post-traumatic and postischemic lesions, as well as defects proper to normal aging and neurodegenerative diseases, that is, principally Alzheimer's disease. Pregnenolone, the main steroid synthesized from cholesterol in the nervous system (therefore, a neurosteroid), binds specifically with high affinity (> or = 40 nM) to microtubule-associated protein 2 (MAP2), a protein family involved in the assembly and stabilization of microtubules made from tubulin alpha and beta polymers, and in the bundling of several microtubules by MAP2 projection arms. Pregnenolone binding increases MAP2-induced microtubule polymerization, when purified tubulin and MAP2 are coincubated in GTP containing buffer at 37 degrees C. Therefore, MAP2 can be considered as a receptor for a novel mechanism of steroid action. The underlying principle and its potential pharmacological consequences are described in an INSERM patent (FR 0003430; March 17, 2000). MAPREG has established its own laboratory in a space rented to Bicêtre hospital, near the research building of INSERM, where two of the main founders of the company (Drs. E. Baulieu and P. Robel) work. The company has been quite successful, largely thanks to the support of ISOA (attributed in October 2002). A lead compound (pregnenolone derivative) was tested and patented by MAPREG early in 2003 (FR 0300507; January 17, 2003). Activities and results reported at the ISOA meeting on Oct. 2, 2003, include in vitro basic studies, in vitro and in vivo neuroprotection trials in rodent systems, and studies with human cells and an AD transgenic mouse model.