Alpharetroviruses provide a useful system for the study of the molecular mechanisms of host range and receptor interaction. These viruses can be divided into subgroups based on diverse receptor usage due to variability within the two host range determining regions, hr1 and hr2, in their envelope glycoprotein SU (gp85). In previous work, our laboratory described selection from a subgroup B avian sarcoma-leukosis virus of an extended-host-range variant (LT/SI) with two adjacent amino acid substitutions in hr1. This virus retains its ability to use the subgroup BD receptor but can also infect QT6/BD cells, which bear a related subgroup E receptor (R. A. Taplitz and J. M. Coffin, J. Virol 71:7814-7819, 1997). Here, we report further analysis of this unusual variant. First, one (L154S) of the two substitutions is sufficient for host range extension, while the other (T155I) does not alter host range. Second, these mutations extend host range to non-avian cell types, including human, dog, cat, mouse, rat, and hamster. Third, interference experiments imply that the mutants interact efficiently with the subgroup BD receptor and possibly the related subgroup E receptor, but they have another means of entry that is not dependent on these interactions. Fourth, binding studies indicate that the mutant SU proteins retain the ability to interact as monomers with subgroup BD and BDE receptors but only bind the subgroup E receptor in the context of an Env trimer. Further, the mutant SU proteins bind well to chicken cells but do not bind any better than wild-type subgroup B to QT6 or human cells, even though the corresponding viruses are capable of infecting these cells.Alpharetroviruses, or avian sarcoma-leukosis viruses (ASLVs), display a great deal of diversity in their envelope glycoprotein (Env) sequences leading to diverse host range but, with the exception of the long terminal repeat (LTR), are nearly identical throughout the remainder of their genomes (11, 15, 16, 25-27, 29, 42). This pattern suggests a response to selective pressures to replicate in a variety of hosts. Alpharetroviruses are divided into subgroups (A to J) depending on host range, superinfection resistance patterns, and neutralizing antibody cross-reactivity. The surface (SU) subunit of the envelope glycoprotein is responsible for receptor recognition. Through a poorly characterized process, probably requiring a low-pH step (34), the SU-receptor interaction triggers the transmembrane (TM) subunit to mediate fusion between the viral envelope and the target cell membrane (10,26,48).Receptors for ASLV of subgroups A, B, D, and E have been cloned. The receptor for subgroup A viruses is a low-density lipoprotein receptor-like protein and is unrelated to any other known retroviral receptor (5, 51). The receptors for B, D, and E are encoded by orthologous genes in the tumor necrosis factor receptor family (2,3,8,40). Chickens have two alleles capable of acting as the receptor for these viruses. , conferring susceptibility to infection by subgroup E but not subgr...

Recombinant adeno-associated virus (rAAV)-based gene therapy represents a promising approach for the treatment of heart muscle diseases, but the molecular mechanisms that direct rAAV transduction remain unclear. Here we demonstrate that β-adrenergic receptor stimulation with isoproterenol (ISO) markedly increased cardiomyocyte transduction of rAAV in vitro and in vivo. Conversely, chronic β-adrenergic receptor downregulation significantly suppressed rAAV transduction. Pretreatment with calcium signaling cascade inhibitors including calcineurin inhibitory peptide (CNIP) strongly suppressed the positive effects of ISO on rAAV transduction. Additionally we document that ISO treatment led to a significant increase in double-stranded (ds) DNA synthesis of the rAAV genome and an increase in promoter activity. Moreover, stimulation with ISO did not affect rAAV transduction in calcineurin nullizygous mice. Collectively, we conclude that a calcium-dependent pathway regulates rAAV vector transduction at a number of stages that may include vector mobilization, conversion, and transcription activity. Modulating this pathway through β-adrenergic signaling enhances rAAV-mediated gene delivery to cardiomyocytes, and may be valuable when considering therapeutic approaches for heart muscle diseases.