CD4-Independent Human Immunodeficiency Virus Infection Involves Participation of Endocytosis and Cathepsin B

During a comparison of the infectivity of mNDK, a CD4-independent human immunodeficiency virus type 1 (HIV-1) strain, to various cell lines, we found that HeLa cells were much less susceptible than 293T and TE671 cells. Hybridoma cells between HeLa and 293T cells were as susceptible as 293T cells, suggesting that cellular factors enhance the mNDK infection in 293T cells. By screening a cDNA expression library in HeLa cells, cystatin C was isolated as an enhancer of the mNDK infection. Because cathepsin B protease, a natural ligand of cystatin C, was upregulated in HeLa cells, we speculated that the high levels of cathepsin B activities were inhibitory to the CD4-independent infection and that cystatin C enhanced the infection by impairing the excessive cathepsin B activity. Consistent with this idea, pretreatment of HeLa cells with 125 µM of CA-074Me, a cathepsin B inhibitor, resulted in an 8-fold enhancement of the mNDK infectivity. Because cathepsin B is activated by low pH in acidic endosomes, we further examined the potential roles of endosomes in the CD4-independent infection. Suppression of endosome acidification or endocytosis by inhibitors or by an Eps15 dominant negative mutant reduced the infectivity of mNDK in which CD4-dependent infections were not significantly impaired. Taken together, these results suggest that endocytosis, endosomal acidification, and cathepsin B activity are involved in the CD4-independent entry of HIV-1

Turfgrass Reflectance Measurements, Chlorophyll, and Soil Nitrate Desorbed from Anion Exchange Membranes

There is not extensive research on the potential of anion exchange membranes (AEMs) for determining available N in soils of turfgrass systems, nor on the use of reflectance meters for quantifying turfgrass color. The two objectives of this study were to determine relationships between (i) turfgrass color measurements and soil nitrate (NO3–N) desorbed from AEMs and (ii) reflectance meter measurements and turfgrass chlorophyll concentration. A field experiment was conducted on a 90% Kentucky bluegrass (Poa pratensis L.) stand across 2 yr. Anion exchange membranes were inserted into the soil and exchanged weekly. Desorbed NO3–N from the AEMs was quantified. Turfgrass color and chlorophyll measurements were taken monthly. Reflectance meter measurements were significantly related to chlorophyll concentration. Linear response plateau models suggested critical levels of AEM soil NO3–N, above which turfgrass color did not improve, from 0.31 to 0.43 µg cm–2 d–1. These models suggest that critical levels of soil NO3–N could be determined that maximize turfgrass quality without excessive N application. These findings suggest both AEMs and hand-held reflectance meters could be useful tools for N management in turfgrass