A locally invasive giant cell tumor of the skull base: case report.

Giant cell tumors (GCTs) are rare, usually affecting the epiphyses in long bones of the extremities. They seldom occur in the skull, where they preferentially affect the sphenoid and temporal bones. Considered to be benign, locally aggressive lesions, they may cause cranial nerve deficits by compression but infrequently invade the dura and parenchyma of the brain. Several case reports with follow-up describe gross total resection of skull base GCT to be curative. Anything short of total resection usually results in recurrence within 4 years. Radiation therapy, although controversial, is reserved for lesions that cannot be completely resected. Some argue, however, against the use of radiation because there are reported cases of malignant transformation. Here we describe the case of a large GCT that was invasive to the dura, temporal lobe, as well as the third division of the trigeminal nerve, and to date gross total resection has been curative of this lesion. The patient has not undergone radiation therapy.

The CorA Mg2+ transport protein of Salmonella typhimurium. Mutagenesis of conserved residues in the third membrane domain identifies a Mg2+ pore.

The CorA transport system is the major Mg2+ influx pathway for bacteria and the Archaea. CorA contains three C-terminal transmembrane segments. No conserved charged residues are apparent within the membrane, suggesting that Mg2+ influx does not involve electrostatic interactions. We have mutated conserved residues within the third transmembrane segment to identify sites involved in transport. Mutation of conserved aromatic residues at either end of the membrane segment to alternative aromatic amino acids did not affect total cation uptake or cation affinity. Mutation to alanine greatly diminished uptake with little change in cation affinity implying that the conserved aromatic residues play a structural role in stabilizing this membrane segment of CorA at the interface between the bilayer and the aqueous environment. In contrast, mutation of Tyr292, Met299, and Tyr307 greatly altered the transport properties of CorA. Y292F, Y292S, Y292C, or Y292I mutations essentially abolished transport, without effect on expression or membrane insertion. M299C and M299A mutants exhibited a decrease in cation affinity for Mg2+, Co2+, or Ni2+ of 10-50-fold without a significant change in uptake capacity. Mutations at Tyr307 had no significant effect on cation uptake capacity; however, the affinity of Y307F and Y307A mutations for Mg2+ and Co2+ was decreased 3-10-fold, while affinity for Ni2+ was unchanged compared with the wild type CorA. In contrast, the affinity of the Y307S mutant for all three cations was decreased 2-5-fold. Projection of the third transmembrane segment as an alpha-helix suggests that Tyr292, Met299, and Tyr307 all reside on the same face of the alpha-helix. We interpret the transport data to suggest that a hydroxyl group is important at Tyr307, and that these three residues interact with Mg2+ during transport, forming part of the cation pore or channel within CorA.