Cryptococcus neoformans is a facultative intracellular pathogen and its interaction with macrophages is a key event determining the outcome of infection. Urease is a major virulence factor in C. neoformans but its role during macrophage interaction has not been characterized. Consequently, we analyzed the effect of urease on fungal-macrophage interaction using wild-type, urease-deficient and urease-complemented strains of C. neoformans. The frequency of non-lytic exocytosis events was reduced in the absence of urease. Urease-positive C. neoformans manifested reduced and delayed intracellular replication with fewer macrophages displaying phagolysosomal membrane permeabilization. The production of urease was associated with increased phagolysosomal pH, which in turn reduced growth of urease-positive C. neoformans inside macrophages. Interestingly, the ure1 mutant strain grew slower in fungal growth medium which was buffered to neutral pH (pH 7.4). Mice inoculated with macrophages carrying urease-deficient C. neoformans had lower fungal burden in the brain than mice infected with macrophages carrying wild-type strain. In contrast, the absence of urease did not affect survival of yeast when interacting with amoebae. Because of the inability of the urease deletion mutant to grow on urea as a sole nitrogen source, we hypothesize urease plays a nutritional role involved in nitrogen acquisition in the environment. Taken together, our data demonstrate that urease affects fitness within the mammalian phagosome, promoting non-lytic exocytosis while delaying intracellular replication and thus reducing phagolysosomal membrane damage, events that could facilitate cryptococcal dissemination when transported inside macrophages. This system provides an example where an enzyme involved in nutrient acquisition modulates virulence during mammalian infection.

The ataxia-telangiectasia mutated (ATM) gene codifies for a protein critically involved in the cellular response to DNA damage. ATM alterations have been observed in some sporadic lymphoproliferative disorders. The recurrent 11q22-23 deletions found in mantle cell lymphoma (MCL) suggest that ATM could be inactivated in these lymphomas. In this study, ATM gene alterations and protein expression were examined in 20 and 17 MCL tumor specimens, respectively. Previously, these patients had been examined for p53 and p14 ARF gene status and analyzed by comparative genomic hybridization. Nine patients had 11q22-23 losses. Eight ATM gene mutations were detected in 7 patients. These alterations were 3 missense mutations in the phosphatidylinositol-3 kinase (PI-3K) domain and 5 truncating mutations, including 3 frameshifts, a nonsense mutation, and a substitution of the initial methionine. All truncating mutations were associated with lack of protein expression. Somatic origin was demonstrated in 3 mutations, whereas one mutation was carried heterozygously in the patient germ line. Chromosomal imbalances were significantly higher in typical MCL with ATM inactivation (7.8 ؎ 1.3) than in tumors with the wildtype gene (3 ؎ 1.1) (P ‫؍‬ .001). Moreover, tumors with bi-allelic ATM alteration were associated with 3q gains (P ‫؍‬ .015) and frequent extranodal involvement (P ‫؍‬ . IntroductionMantle cell lymphoma (MCL) is a lymphoproliferative disorder characterized by the t(11;14) (q13;q32) translocation, which leads to the rearrangement and overexpression of the cyclin D1 gene. 1,2 However, the tumorigenic and transforming potential of cyclin D1 in experimental models is relatively limited, and it requires the cooperation of other oncogenic factors such as c-myc. 3 Additional alterations in the tumor suppressor genes p16 INK4a and p53 have been described in aggressive variants of MCL, suggesting that these genes may cooperate with cyclin D1 overexpression in the progression of these lymphomas. [4][5][6][7] Classical cytogenetic and comparative genomic hybridization (CGH) studies have shown a high number of recurrent chromosomal alterations in MCL, indicating that other genes may be involved in the pathogenesis of these tumors. [8][9][10] One of the most frequent secondary chromosomal aberrations in MCL is the loss of the 11q22-23 region, where the ataxia-telangiectasia mutated (ATM) gene is located. 11,12 Mutations in the ATM gene are responsible for the ataxiatelangiectasia (AT) syndrome, a rare autosomal recessive disorder characterized by progressive cerebellar ataxia, ocular telangiectasia, immunodeficiency, high sensitivity to ionizing radiation, and predisposition to lymphoid malignancies. 13 AT cells show chromosomal instability, telomere shortening, and defects in response to ionizing radiation and radiomimetic drugs. 14 Mutations and deletions in the ATM gene have also been found in a variety of sporadic neoplasias, including T-prolymphocytic leukemia (T-PLL) 15-17 and B-cell chronic lymphocytic leukemia (B-CLL). 18,19 ...

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