37
| 2 | 2011
Klinisk Biokemi i Norden
(
Fortsætter side 38)
eased patients may then provide baseline references of
miRNA expression profiles. In general, human miRNAs
are sparsely expressed compared to mRNA levels. Some
miRNAs have shown to be abundant in most tissues,
whereas other miRNA groups seem confined to specific
tissues or organs (15). Only a minority of miRNAs are
truly cell specific(brain specific miR-219), but a lot of
cells show a cell-specific miRNA-profile, e.g a pattern
with combinations of miRNAs Universally expressed
miRNAs have been proposed as candidates participat-
ing fundamental metabolic pathways of all normal
cells. It is believed that miRNAs positioned in intron
regions frequently inherit the same expression patterns
to their host genes. miRNAs, which belong to the same
differentially expressed group, are often located within
the same genomic cluster, suggesting the presence of
common regulatory mechanisms (15).
miRNA in health and disease
It is now well accepted that miRNAs act as important
regulators in a vast number of essential, biological pro-
cesses and that the miRNAs can alter their expression
levels accordingly to meet the cellular demands (2).
In addition, cell-specific miRNA-expression profiles
have been reported for several diseases, especially for
cancers, thus indicating that specific miRNAs may cor-
relate well with pathological development (16). Moreo-
ver, it has been shown that miRNAs are aberrantly
expressed or mutated in different cancers, suggesting
that miRNAs may represent a novel class of oncogenes
or tumor suppressor genes, depending on the targets
they regulate. miRNA genes have shown to be located
in chromosomal regions often subject to rearrange-
ments, deletions and amplification in malignant cells.
The prognostic potential of miRNAs has been demon-
strated for several diseases, but especially for different
types of malignancies where miRNA expression profiles
have displayed signatures related to tumor classifica-
tion, diagnosis, and disease-progression (17,18). As
expression patterns of miRNAs seem to correlate with
tissue of origin, clinical cancer behavior and prognosis,
miRNAs may prove to be valuable, new tissue-based
biomarkers in oncology.
miRNA as biomarkers
Whereas cell-based miRNA expression profiles already
has been identified as a promising tool for monitoring
Foto: Henrik Alfthan
