IRAIN (IGF1R antisense imprinted non-protein coding RNA, IGF1R-AS), a 5.3 kb antisense transcript
originating in intron 1 of IGF1R, showed monoallelic paternal expression in five informative
peripheral blood samples (Sun J et al,
2014; Kang L et al, 2015).
Monoallelic expression was detected in 18 breast cancers, in three additional blood samples, in KG-1
and KG-1a haematopoietic cell lines, and in MCF-7 breast cancer cells (Kang L et al, 2015).
At its promoter region, the CpG island showed methylated and unmethylated alleles in one normal
haematopoietic stems cell sample, in KG-1 cells, in three acute myeloid leukaemia samples, and in
two breast cancer samples, but dense methylation of all alleles for K562 cells and total
unmethylation in MCF-7 and MDA-MB-231 breast cancer cell lines, in four breast cancer samples and in
three blood samples (Sun J et al, 2014; Kang L et al, 2015).
The allele usage is interesting in that in 23 of 26 samples the expressed allele was the "A" allele
(Sun J et al, 2014; Kang L et al, 2015).
Another unusual feature is that in two breast cancers the expressed allele was the "G" allele while
in the blood from the same patients that "A" allele was expressed (Kang L et al, 2015). This allele switching
together with the non-statistically significant number of cases (5) in which paternal expression was
documented, suggest that the imprinting status of IRAIN should be regarded as provisional.