Hypersecretion of mucus characterizes many inflammatory airway
diseases, including asthma, chronic bronchitis, and cystic fibrosis. Excess
mucus causes airway obstruction, reduces pulmonary function, and can lead to
increased morbidity and mortality. MicroRNAs are small non-coding pieces of RNA
which regulate other genes by binding to a complementary sequence in the target
mRNA. The microRNA miR-21 is upregulated in many inflammatory conditions and,
interestingly, miR-21 has been shown to target the mRNA of Myristoylated
Alanine-Rich C Kinase Substrate (MARCKS), a protein that is an important
regulator of airway
mucin (the solid component of mucus) secretion.
In this paper, the authors determined that exposure of primary,
well-differentiated, normal human bronchial epithelial (NHBE) cells to the
pro-inflammatory stimulus lipopolysaccharide (LPS) increased expression of both
miR-21 and MARCKS in a time-dependent manner. To investigate whether miR-21
regulation of MARCKS played a role in mucin secretion, two separate airway
epithelial cell lines, HBE1 (papilloma virus transformed) and NCI-H292
(mucodepidermoid derived) were utilized, since manipulation of miR-21 was
performed via transfection of commercially-available miR-21 inhibitors and
mimics/activators. The result showed that treatment of HBE1 cells with LPS
caused concentration-dependent increased in expression of both miR-21 and
MARCKS mRNA and protein. The miR-21 inhibitor effectively reduced levels of
miR-21 in the cells, coincident with an increase in MARCKS mRNA expression over time as well as
enhanced mucin secretion, while the miR-21 mimic/activator increased levels of
miR-21, which coincided with a decrease in
expression of MARCKS and a decrease in mucin secretion.
In conclusion, miR-21 is increased in airway epithelial cells
following exposure to LPS, and that miR-21 downregulates expression of MARCKS,
which may decrease mucin secretion by the cells. Thus, miR-21 may act as a negative
feedback regulator of mucin secretion in airway epithelial cells, and may do
so, at least in part, by downregulating expression of MARCKS.
Full
access: http://mrw.so/j2Grh
Image
by T KONI, from Flickr-cc.
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