M-phase promoting factor (MPF), a complex composed of cdc2 and a B-type cyclin, is a key regulator of the G2/M transition of the cell cycle. The activation of MPF is essential for the proper timing of mitotic events. It has been demonstrated that MPF is regulated by phosphorylation events of both cdc2 and cyclin B1. Specifically, phosphorylation of cyclin B1 has been demonstrated to precede the nuclear localization of MPF. Once nuclear, MPF phosphorylates many of the nuclear components involved in mitosis. Therefore, it appears that phosphorylation of cylin B1 triggers the nuclear localization of MPF. Yet the mechanism of MPF localization due to cyclin B1phosphorylation remained a mystery.

We employed a yeast two-hybrid screen to identify potential protein(s) involved in the subcellular localization of phosphorylated cyclin B1. Surprisingly, one clone isolated from this screen was patched1 (ptc1). Ptc1 is a tumor suppressor localized at the plasma membrane and contains 12 transmembrane spanning regions. Mutations in ptc1 have been demonstrated, to a large degree, to be responsible for Nevoid Basal Cell Carcinoma Syndrome (NBCCS) and basal cell carcinoma (BCC) development. We demonstrated that ptc1 binds to phosphorylated cyclin B1 to retain MPF at the plasma membrane, which in effect inhibits mitotic progression. These findings demonstrate that ptc1 participates in the regulation of MPF and suggest a link between the tumor suppressor activity of ptc1 and cell division. We also examined the effects that mutant ptc1 protein(s) have, as reported in patients with NBCCS/BCC, in the regulation of MPF.

PUBLICATIONS (resulting from this training, and some recent ones)

Kong M, Barnes EA, Ollendorff V, Donoghue DJ. (2000) Cyclin F regulates the nuclear localization of cyclin B1 through a cyclin-cyclin interaction. EMBO J. 19:1378-88.

Barnes EA, Kong M, Ollendorff V, Donoghue DJ. (2001) Patched1 interacts with cyclin B1 to regulate cell cycle progression. EMBO J. 20:2214-23.

Porter LA, Dellinger RW, Tynan JA, Barnes EA, Kong M, Lenormand JL, Donoghue DJ. (2002) Human Speedy: a novel cell cycle regulator that enhances proliferation through activation of Cdk2. J. Cell Biol. 157:357-366.

Barnes EA, Porter LA, Lenormand JL, Dellinger RW, Donoghue DJ. (2003) Human Spy1 promotes survival of mammalian cells following DNA damage. Cancer Res. 63:3701-7.

Barnes, E. A., K. J. Heidtman, D. J. Donoghue (2005) Constitutive activation of the Shh-Ptc1 pathway by a patched1 mutation identified in BCC. Oncogene 24:902-9 15.

Mak BC, Kenerson HL, Aicher LD, Barnes EA, Yeung RS. (2005) Aberrant beta-catenin signaling in tuberous sclerosis. Am J Pathol.167:107-16.