Macrophage colony-stimulating factor expression in retrovirally transduced cells is dependent upon both the adherence status of the target cells and its 5′ flanking untranslated region

Numerous cell types retrovirally transduced with macrophage colony-stimulating factor (M-CSF) using LXSN-based vectors showed a variable expression of the transgene. Expression of M-CSF correlated with the cells' adherent status. Transduced adherent cells produced the M-CSF, whereas the non-adherent cells synthesized little M-CSF. Studies showed that the 5′-UTR of the M-CSF gene regulated transgenic M-CSF gene expression. Ligation of this 5′-UTR to the enhanced green fluorescent protein gene (EGFP) caused the expression of EGFP to show the same dichotomy as previously seen with the M-CSF. Transgenic M-CSF was expressed within non-adherent cells when the 5′-UTR was removed from the LXSN vector. Quantitative real-time polymerase chain reaction analysis confirmed that lesser production of M-CSF mRNA occurred within the non-adherent cells than in the adherent cells. This difference was eliminated when the 5′-UTR was removed from the retroviral vector. Our work suggests that this 5′-UTR of the M-CSF gene could be an important way to get transgenic expression within adherent cells, but not in non-adherent cells.