A conserved gene antisense to the proto-oncogene c-RAF encodes a
multi-zinc-finger protein, MAKORIN2. T.A. Gray1, K.
Azama2, K. Whitmore1, A. Min1, S.
Abe2, R.D. Nicholls1. 1) Dept Genetics, Case Western
Reserve Univ, Cleveland, OH; 2) Faculty of Agriculture, Ehime Univ., Matsuyama,
Japan.
High levels of c-RAF proto-oncogene
expression occur in some human lung cancers, and recent studies have shown that
over-expression of wildtype c-Raf in a mouse model leads to an increased
incidence of lung tumorigenesis. The c-RAF proto-oncogene can be
downregulated by antisense oligonucleotide therapy, culminating in a reduced
growth rate for treated cells. Combined, the data suggest that regulation of
c-RAF expression is an important factor in some cancers. Here, we
describe a novel gene, MAKORIN RING zinc-finger
2 (MKRN2), that overlaps and is antisense to c-RAF.
Northern blot analyses show that human and mouse MKRN2 and c-RAF
are concurrently transcribed, suggesting that the mRNA products may form RNA
duplexes. We have also identified MKRN2 orthologs in fish and birds,
placing the gene duplication event that gave rise to this locus early in
vertebrate evolution, at least 450 million years ago. All MAKORIN2 orthologs are
well-conserved (56%-93% amino acid identity) and retain the hallmark RING and
C3H zinc-finger composition of the MAKORIN protein family. While the function of
MAKORIN2 is unknown, RING and C3H zinc-fingers suggest macromolecular and
ribonucleoprotein roles, respectively, and poxviral derivatives homologous to
the MAKORIN protein family circumvent apoptotic pathways. Taken together, our
data identify a conserved vertebrate MKRN2 gene that overlaps the
c-RAF locus in a tail-to-tail orientation. The conservation of this
arrangement implies that it is evolutionarily advantageous, possibly due to
co-regulation of the MKRN2 and c-RAF antisense mRNA and/or protein
products. Present studies are examining a functional link between MKRN2
and c-RAF, and evaluating MKRN2 for disruption in human cancers.