RNA Levels of Human Retrovirus Receptors Pit1 and Pit2 Do Not Correlate with Infectibility by Three Retroviral Vector Pseudotypes

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Abstract
The gibbon ape leukemia virus (GaLV) and the amphotropic murine leukemia virus (A-MuLV) infect human cells via specific receptors, Pit1 and Pit2, respectively. mRNA levels of these receptors were determined by Northern analysis and for Pit2 in addition by quantitative RT-PCR. Pit1 and Pit2 were expressed in different amounts in human tissues and cell lines; Pit1-specific mRNA was generally more abundant than Pit2 mRNA. No correlation was found between Pit1 and Pit2 RNA levels and infectibility by GaLV and A-MuLV pseudotyped vectors, respectively. GaLV and A-MuLV revealed a partial reciprocal interference. MuLV-10A1 can utilize both Pit1 and Pit2 for entry into cells but could not infect any of the 14 human cell lines more efficiently than A-MuLV or GaLV. Interference assays suggested that MuLV-10A1 has a higher affinity for and infected most cells predominantly by Pit2. However, at least in one cell line it used Pit1 more efficiently for entry. We conclude that (1) Pit1 and Pit2 mRNA levels in human cells are not indicative of the infectibility by GaLV and A-MuLV pseudotypes, respectively; (2) A-MuLV can infect target cells as efficiently as can GaLV, although Pit2 RNA is less abundant than Pit1 RNA; (3) factor(s) in addition to the presence of Pit1 and Pit2 are involved in retroviral infection; and (4) MuLV-10A1 pseudotype does not infect human cells more efficiently than do A-MuLV and GaLV pseudotypes. Gibbon ape leukemia virus (GaLV) and amphotropic murine leukemia virus (A-MuLV) pseudotyped retroviral vectors infect human cells via their specific receptors Pit1 and Pit2, respectively. Both receptors belong to the same family of sodium-dependent phosphate transporters. Knowledge of Pit1 and Pit2 expression is useful for the development and improvement of gene transfer protocols based on both vector pseudotypes. To investigate expression of the human receptors for GaLV and A-MuLV we have analyzed their mRNA levels in various human tissues and cell lines by Northern transfer hybridization and competitive PCR. We found no correlation between Pit1 and Pit2 mRNA levels and infectibility by GaLV and A-MuLV pseudotyped vectors, respectively. Thus, factors in addition to retroviral receptor expression are likely to play an important role in the transducibility of target cells. Moreover, retroviral vectors pseudotyped by MuLV-10A1, an amphotropic MuLV isolate that can utilize both the GaLV and the A-MuLV receptor for entry into cells, could not infect any of 14 human cell lines more efficiently than did GaLV or A-MuLV pseudotypes.