Resistance to small-molecule CCR5 inhibitors arises when HIV-1 variants acquire the ability to use inhibitor-bound CCR5 while still recognizing free CCR5. Two isolates, CC101.19 and D1/85.16, became resistant via four substitutions in the gp120 V3 region and three in the gp41 fusion peptide (FP), respectively. The binding characteristics of a panel of monoclonal antibodies (MAbs) imply that several antigenic forms of CCR5 are expressed at different levels on the surfaces of U87-CD4-CCR5 cells and primary CD4؉ T cells, in a cell-typedependent manner. CCR5 binding and HIV-1 infection inhibition experiments suggest that the two CCR5 inhibitor-resistant viruses altered their interactions with CCR5 in different ways. As a result, both mutants became generally more sensitive to inhibition by CCR5 MAbs, and the FP mutant is specifically sensitive to a MAb that stains discrete cell surface clusters of CCR5 that may correspond to lipid rafts. We conclude that some MAbs detect different antigenic forms of CCR5 and that inhibitor-sensitive and -resistant viruses can use these CCR5 forms differently for entry in the presence or absence of CCR5 inhibitors.The small-molecule CCR5 inhibitors maraviroc (MVC) and vicriviroc (VVC) are, or have been, used to treat human immunodeficiency virus type 1 (HIV-1) infection. They bind in the transmembrane helices and stabilize CCR5 in a conformation the viral Env complex cannot use efficiently (14,26,47). Resistant viruses usually gain the ability to enter cells via inhibitor-bound CCR5 while retaining the use of free CCR5 (46, 57). Virus-CCR5 binding involves interactions between the Tyr-sulfated N terminus (NT) and the second extracellular loop (ECL2) of the coreceptor and the 4-stranded bridging sheet and V3 region of the gp120 glycoprotein, respectively (20,21). In the most common genetic route to resistance, multiple sequence changes in V3 make the virus more dependent on the CCR5 NT (4,7,27,(37)(38)(39)55). A much rarer pathway involves changes in the fusion peptide (FP) of the gp41 protein, but the resistance mechanism is unknown (3). These pathways were followed when resistant isolates CC101.19 and D1/85.16 were derived from CC1/85 under selection by two similar inhibitors, AD101 and VVC, in peripheral blood mononuclear cells (PBMCs); the most critical resistance-associated substitutions in the escape mutant viruses were four in V3 and three in the FP (27,33). In this study, we used infectious Env chimeric clones, Res-4V3 derived from CC101.19 and Res-3FP from D1/85.16, together with the parental clones Par-4V3 and Par-3FP, derived from CC1/85, which were chosen based on sequence similarities with Res-4V3 and Res-3FP (7).The HIV-1 coreceptors CCR5 and CXCR4 exist in heterogeneous forms (6, 29), influenced by factors such as posttranslational modifications, coupling to G proteins, and the lipid environment (5,8,15,34,35). CCR5 monoclonal antibodies (MAbs) can vary considerably in how they stain different cell types in a way that is not always explained by CCR5 expression levels (1...

Cyclophilin B (CypB) is a 21-kDa protein with peptidyl-prolyl cis-trans isomerase activity that functions as a transcriptional inducer for Stat5 and as a ligand for CD147. To better understand the global function of CypB in breast cancer, T47D cells with a small interfering RNA-mediated knockdown of CypB were generated. Subsequent expression profiling analysis showed that 663 transcripts were regulated by CypB knockdown, and that many of these gene products contributed to cell proliferation, cell motility, and tumorigenesis. Real-time PCR confirmed that STMN3, S100A4, S100A6, c-Myb, estrogen receptor alpha, growth hormone receptor, and progesterone receptor were all down-regulated in si-CypB cells. A linkage analysis of these array data to protein networks resulted in the identification of 27 different protein networks that were impacted by CypB knockdown. Functional assays demonstrated that CypB knockdown also decreased cell growth, proliferation, and motility. Immunohistochemical and immunofluorescent analyses of a matched breast cancer progression tissue microarray that was labeled with an anti-CypB antibody demonstrated a highly significant increase in CypB protein levels as a function of breast cancer progression. Taken together, these results suggest that the enhanced expression of CypB in malignant breast epithelium may contribute to the pathogenesis of this disease through its regulation of the expression of hormone receptors and gene products that are involved in cell proliferation and motility.

CCR5 acts as the principal coreceptor during HIV-1 transmission and early stages of infection. Efficient HIV-1 entry requires a series of processes, many dependent on the conformational state of both viral envelope protein and cellular receptor. Monoclonal antibodies (MAbs) are able to identify different CCR5 conformations, allowing for their use as probes to distinguish CCR5 populations. Not all CCR5 MAbs are able to reduce HIV-1 infection, suggesting the use of select CCR5 populations for entry. In the U87.CD4.CCR5-GFP cell line, we used such HIV-1-restricting MAbs to probe the relation between localization, trafficking and G protein association for individual CCR5 conformations. We find that CCR5 conformations not only exhibit different localization and abundance patterns throughout the cell, but that they also display distinct sensitivities to endocytosis inhibition. Using chemokine analogs that vary in their HIV-1 inhibitory mechanisms, we also illustrate that responses to ligand engagement are conformation-specific. Additionally, we provide supporting evidence for the select sensitivity of conformations to G protein association. Characterizing the link between the function and dynamics of CCR5 populations has implications for understanding their selective targeting by HIV-1 and for the development of inhibitors that will block CCR5 utilization by the virus.

Diabetes results in increased fracture risk, and advance glycation endproducts (AGEs) have been implicated in this pathophysiology. S100 proteins are ligands for the receptor of AGEs (RAGE). An intracellular role of the S100 family member S100A4 (Mts1) to suppress mineralization has been described in pre-osteoblastic MC3T3-E1 cells. However, S100 proteins could have additional effects on bone. The goal of the current study was to determine effects of increased extracellular S100 on osteoclastogenesis. We first determined the direct effects of S100 on pre-osteoclast proliferation and osteoclastic differentiation. RANKL-treated RAW 264.7 cell proliferation and TRAP activity were significantly inhibited by S100, and the number and size of TRAP-positive multinucleated cells were decreased. We then determined whether S100 could affect osteoclastogenesis by an indirect process by examining effects of conditioned media from S100-treated MC3T3-E1 cells on osteoclastogenesis. In contrast to the direct inhibitory effect of S100, the conditioned media promoted RAW 264.7 cell proliferation and TRAP activity, with a trend toward increased TRAP-positive multinucleated cells. S100 treatment of the MC3T3-E1 cells for 14 days did not significantly affect alkaline phosphatase, M-CSF, or OPG gene expression. RANKL was undetectable in both untreated and treated cells. The treatment slightly decreased MC3T3-E1 cell proliferation. Interestingly, S100 treatment increased expression of RAGE by the MC3T3-E1 cells. This suggested the possibility that S100 could increase soluble RAGE, which acts as a decoy receptor for S100. This decrease in availability of S100, an inhibitor of pre-osteoclast proliferation, could contribute to osteoclastogenesis, ultimately resulting in increased bone resorption.