Disproportionate relationship between APOBEC-1 expression and apolipoprotein B mRNA editing activity.
Apolipoprotein B (apoB) mRNA editing is a site-specific (nucleotide 6666) cytidine to uridine transition catalyzed by a cytidine deaminase, APOBEC-1, in the context of a multiprotein complex referred to as the C/U editosome. This report quantifies for the first time the effect of altering APOBEC-1 protein abundance on the proportion of edited apoB mRNAs using transfected McArdle rat hepatoma cells which had been sorted by flow cytometry into populations expressing different levels of green fluorescent protein-APOBEC-1 chimera, GFP-APOBEC. A correlation was observed in which increased expression of GFP-APOBEC protein resulted in a higher proportion of edited apoB mRNA. The number of enzyme molecules required to increase the proportion of edited apoB RNAs was disproportionately high relative to that which might have been predicted from a typical catalytic relationship. Moreover, editing of apoB mRNA at inappropriate sites (promiscuous editing) occurred in response to overexpressing GFP-APOBEC. The data suggest that experimental manipulation of APOBEC-1 abundance in the absence of other regulatory considerations will always result in some level of promiscuous editing. Coordinate expression of APOBEC-1 and the auxiliary proteins and/or regulation of their interactions may be required to increase editing activity without losing editing-site fidelity.
Siddiqui
J F
JF
Department of Biochemistry and Biophysics, Health Science, University of Rochester School of Medicine and Dentistry, 601 Elmwood Avenue, Rochester, New York 14642, USA.
Van Mater
D
D
Sowden
M P
MP
Smith
H C
HC
D000071479:APOBEC-1 Deaminase; D000818:Animals; D001055:Apolipoproteins B / Q000235:genetics*; D001483:Base Sequence; D003564:Cytidine Deaminase / Q000235:genetics* / Q000378:metabolism*; D017931:DNA Primers / Q000235:genetics; D015870:Gene Expression; D049452:Green Fluorescent Proteins; D008114:Liver Neoplasms, Experimental / Q000235:genetics / Q000378:metabolism; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D017393:RNA Editing; D012333:RNA, Messenger / Q000235:genetics* / Q000378:metabolism*; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D014407:Tumor Cells, Cultured; D000098830:AICDA (Activation-Induced Cytidine Deaminase)
D001055:Apolipoproteins B; D017931:DNA Primers; D008164:Luminescent Proteins; D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; D000098830:AICDA (Activation-Induced Cytidine Deaminase); D000071479:APOBEC-1 Deaminase; C000605091:Apobec1 protein, rat; D003564:Cytidine Deaminase