CODING REGION-SPECIFIC DESTABILIZATION OF MESSENGER-RNA TRANSCRIPTS ATTENUATES EXPRESSION FROM RETROVIRAL VECTORS CONTAINING CLASS-1 ALDEHYDE DEHYDROGENASE CDNA

Class 1 aldehyde dehydrogenases (ALDH-1) function as drug resistance g ene products by catalyzing the irreversible conversion of aldophospham ide, an active metabolite of cyclophosphamide, to an inert compound. B ecause the dose-limiting toxicity of cyclophosphamide is myelosuppress ion, retrovirus-mediated transfer of ALDH-1 to bone marrow cells has b een proposed as a protective strategy. Here we show that expression of ALDH-1 vectors was problematic due to low levels of ALDH-1 mRNA accum ulation, A number of vectors containing several different ALDH-1 cDNAs were introduced into a variety of different cell lines either by tran sfection or transduction. Detectable ALDH-1 protein and enzyme activit y was only seen in one transfected cell clone, Cells transduced with A LDH-1 retroviral vectors had no detectable protein expression and very low levels of ALDH-1 mRNA, Analogous vectors containing other drug re sistance cDNAs led to much higher levels of steady-state mRNA, The mRN A half-life from ALDH-1 vectors was less than 2 hr suggesting that vec tor-derived mRNAs were destabilized by ALDH-1 coding sequences. These results suggest that methods which increase the stability of ALDH-1 mR NAs will be important for increased drug resistance in retrovirally tr ansduced hematopoietic cells.