CXCR4, a G-protein-coupled receptor of CXCL12/stromal cell-derived factor-1a, mediates a wide range of physiological and pathological processes, including the targeted metastasis of cancer cells. CXCR4 has been shown to homo-oligomerize in several experimental systems. However, it remains unclear with which domains CXCR4 interacts homotypically, and whether it dimerizes or forms a higher-order complex. To address these issues, we used bioluminescent resonance energy transfer and bimolecular fluorescence complementation analyses to measure the homotypic interactions of CXCR4 in living cells. Both assays indicated that CXCR4 interacts homotypically, which is consistent with previous studies. By studying CXCR4 mutants lacking various domains, we found that multiple transmembrane domains probably serve as potential molecular interaction surfaces for oligomerization. The relative contribution of the amino-or carboxy-termini to oligomerization was small. To differentiate between a dimer and a multimer consisting of more than two molecules, bioluminescent resonance energy transfer-bimolecular fluorescence complementation analysis was conducted. It revealed that CXCR4 engages in higher-order oligomerization in a ligandindependent fashion. This is the first report providing direct experimental evidence for the higher-order multimerization of CXCR4 in vivo. We hypothesize that CXCR4 distributes to the cell surface as a multimer, in order to effectively sense, with increased avidity, the chemotaxis-inducing ligand in the microenvironment. Studying the structure and function of the oligomeric state of CXCR4 may lead us to develop novel CXCR4 inhibitors that disassemble the molecular cluster of CXCR4. (Cancer Sci 2009; 100: 95-102) C XCR4, a widely expressed chemokine receptor of CXCL12/ stromal cell-derived factor (SDF)-1α, plays a role in various physiological and pathological processes, including neuronal network development, normal and malignant cell migration, inflammatory reactions, the genetic immunodeficiency syndrome WHIM (warts, hypogammaglobulinemia, infections, myelok-athexis), and human immunodeficiency virus (HIV)-1 infection.(1-7) The CXCR4-CXCL12/SDF-1α axis is reportedly involved in the tumor progression of breast cancer and more recently of pancreatic, esophageal, prostate, thyroid, colorectal, and cutaneous cancers.(8-16) Thus, it has been emphasized that the CXCR4-CXCL12/SDF-1α axis may be an important therapeutic target. (9,14) Understanding the regulatory mechanisms of CXCR4 functions may provide clues to develop therapeutic approaches for such disorders.CXCR4 was shown to homo-oligomerize by several experimental systems. It is possible that CXCR4 dimerizes because CXCL12/SDF-1α forms a dimer, as indicated by structural analyses.(17-19) However, past biophysical analyses did not critically distinguish between dimers and complexes consisting of more than two molecules (the higher-order oligomer).(20-23) The oligomerization of G protein-coupled recepters (GPCR) has been suggested to play a role in ligand-...

The RNase H activity associated with human immunodeficiency virus type 1 (HIV-1) is an attractive target for an antiretroviral drug development. We screened 20000 small-molecular-weight compounds for RNase H inhibitors and identified a novel RNase H-inhibiting structure characterized by a 5-nitro-furan-2-carboxylic acid carbamoylmethyl ester (NACME) moiety. Two NACME derivatives, 5-nitro-furan-2-carboxylic acid adamantan-1-carbamoylmethyl ester (compound 1) and 5-nitro-furan-2-carboxylic acid [[4-(4-bromo-phenyl)-thiazol-2-yl]-(tetrahydro-furan-2-ylmethyl)-carbamoyl]-methyl ester (compound 2), effectively blocked HIV-1 and MLV RT-associated RNase H activities with IC(50)s of 3-30 microM but had little effect on bacterial RNase H activity in vitro. Additionally, 20-25 microM compound 2 effectively inhibited HIV-1 replication. An in silico docking simulation indicated that the conserved His539 residue, and two metal ions in the RNase H catalytic center are involved in RNase H inhibition by NACME derivatives. Taken together, these data suggest that NACME derivatives may be potent lead compounds for development of a novel class of antiretroviral drugs.

The matrix domain (MA) of human immunodeficiency virus type 1 Pr55Gag is covalently modified with a myristoyl group that mediates efficient viral production. However, the role of myristoylation, particularly in the viral entry process, remains uninvestigated. This study replaced the myristoylation signal of MA with a well-studied phosphatidylinositol 4,5-biphosphate-binding plasma membrane (PM) targeting motif, the phospholipase C-δ1 pleckstrin homology (PH) domain. PH–Gag–Pol PM targeting and viral production efficiencies were improved compared with Gag–Pol, consistent with the estimated increases in Gag–PM affinity. Both virions were recovered in similar sucrose density-gradient fractions and had similar mature virion morphologies. Importantly, PH–Gag–Pol and Gag–Pol pseudovirions had almost identical infectivity, suggesting a dispensable role for myristoylation in the virus life cycle. PH–Gag–Pol might be useful in separating the myristoylation-dependent processes from the myristoylation-independent processes. This the first report demonstrating infectious pseudovirion production without myristoylated Pr55Gag.