Rapamycin Blocks Sexual Development in Fission Yeast through Inhibition of the Cellular Function of an FKBP12 Homolog

Abstract

FKBP12 is a ubiquitous and a highly conserved prolyl isomerase that binds the immunosuppressive drugs FK506 and rapamycin. Members of the FKBP12 family have been implicated in many processes that include intracellular protein folding, transport, and assembly. In the budding yeast Saccharomyces cerevisiae and in human T cells, rapamycin forms a complex with FKBP12 that inhibits cell cycle progression by inhibition of the TOR kinases. We reported previously that rapamycin does not inhibit the vegetative growth of the fission yeast Schizosaccharomyces pombe; however, it specifically inhibits its sexual development. Here we show that disruption of the S. pombe FKBP12 homolog, fkh1 ؉ , at its chromosomal locus results in a mating-deficient phenotype that is highly similar to that obtained by treatment of wild type cells with rapamycin. A screen for fkh1 mutants that can confer rapamycin resistance identified five amino acids in Fkh1 that are critical for the effect of rapamycin in S. pombe. All five amino acids are located in the putative rapamycin binding pocket. Together, our findings indicate that Fkh1 has an important role in sexual development and serves as the target for rapamycin action in S. pombe.

Isp7 Is a Novel Regulator of Amino Acid Uptake in the TOR Signaling Pathway

“…TORC1 also contains the protein Mip1 (raptor in humans), and TORC2 also contains the proteins Ste20 (rictor in humans) and Sin1 (mSin1 in humans) (13)(14)(15)(16)(17)(18)(19)(20). TORC1 is essential under normal growth conditions and plays major roles in the control of cellular growth, possibly in response to nitrogen availability (17,(20)(21)(22)(23)(24)(25). Consistently, most of the genes that are upregulated in tor2 ts mutant cells are involved in the nitrogen starvation response (17).…”

“…More recently, it was shown that rapamycin can inhibit TORC1 in the presence of caffeine, which potentially lowers the kinase activity of TORC1 and induces a nitrogen starvation-like response (32,34). Rapamycin inhibits sexual development and amino acid uptake (20,24,35) and following long exposure reduces the expression of nitrogen starvation-induced amino acid permeases (20). Under certain conditions, rapamycin can also induce sexual development (18), suggesting that rapamycin may involve inhibition of either TORC1 or TORC2, depending on the experimental conditions.…”

Elucidating TOR Signaling and Rapamycin Action: Lessons from Saccharomyces cerevisiae

“…These findings revealed that the antifungal activity of rapamycin in C. neoformans is mediated via conserved complexes involving FKBP12 and TOR homologues. More recently, a TOR1 homologue has also been identified and characterized in the fungal pathogen Candida albicans (37), and TOR1 and TOR2 homologues have been identified and characterized in the fission yeast Schizosaccharomyces pombe (161,162).…”

Loss of the TOR Kinase Tor2 Mimics Nitrogen Starvation and Activates the Sexual Development Pathway in Fission Yeast

“…Fission yeast has two TOR genes, namely tor1 and tor2 (15,48). Fission yeast tor1 is not essential; however, tor1⌬ cells are unable to properly arrest in G 1 in response to nutrient starvation, to initiate sexual differentiation, and to survive under stressed conditions (15,50). These functions are mediated, at least in part, by Gad8, an AGC family protein kinase that functions downstream of Tor1 (25).…”