Ενζυματικές αλλαγές στο cAMP μονοπάτι σηματοδότησης και αλλαγές στην έκφραση των microRNA στην παθογένεση των όγκων του φλοιού των επινεφριδίων
Protein enzymatic changes of the cAMP pathway and microRNA aberrations in the pathogenesis of adrenocortical tumors
Μπιμπάκη, Ειρήνη Ι
Context Bilateral adrenal hyperplasias (BAHs) may be caused by mutations of genes
that code for molecules that participate in cAMP signaling. Little is known about
cAMP signaling in adrenocortical tumors (ADTs) that do not harbor mutations in
known genes. Massive macronodular adrenocortical disease (MMAD) and Primary
pigmented adrenocortical disease (PPNAD), two forms of BAHs may be caused by
aberrant microRNA expression.
Objective We assessed the cAMP signaling pathway by enzymatic and molecular
studies in mutation-negative ADTs. Furthermore, we were interested in identifying
the microRNA profile in MMAD and PPNAD and in detecting putative microRNAgene
target pairs involved in adrenal tumorigenesis.
Design Samples from 27 patients with ADTs (ages 5-60 years) were studied and
compared to normal adrenocortical tissue. All samples were sequenced for GNAS,
PRKAR1A, PDE11A, and PDE8B sequencing defects. Cyclic AMP (cAMP) levels
and binding, protein kinase A (PKA), and phosphodiesterase (PDE) activities were
assayed. Additionally, 10 patients with MMAD (ages 39 - 60 years) and 10 patients
with PPNAD (ages 5-41 years) were studied in order to identify the microRNA
profile; 4 normal adrenal cortices were used as controls. All samples were analyzed
using microRNA microarrays; data were validated by Real Time PCR. MicroRNA
microarray analysis was integrated with expression data in the same MMAD, PPNAD
samples to identify potential microRNA-gene target pairs implicated in adrenal
hyperplasia formation. Using a PPNAD cell line we tried to investigate the regulatory
mechanisms underlying the expression of miR-449.
Results All adenomas were mutation-negative; these tumors had lower PDE activity
levels and higher cAMP binding affinity than normal adrenal. BAHs, both with and
without any mutations, had higher cAMP levels and decreased free PKA activity.
A total of 37 microRNAs, 44 microRNAs were differentially expressed between
MMAD, PPNAD and normal tissues respectively. We also identified putative gene
targets for these microRNAs. After considering various clinical parameters from our
patients, we identified miR-130a and miR-382 as putative diagnostic markers in
MMAD and let-7b in PPNAD. We demonstrate a regulatory mechanism according to
which PKA modulates the expression of miR-449 and its target gene WISP2.
Conclusion: ADTs independently of their mutation status, demonstrated functional
abnormalities of cAMP signaling. It is probable that epigenetic events, microRNA
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implication or additional defects of genes involved in this pathway are responsible.
MicroRNAs appear to have distinct regulatory effects in MMAD and PPNAD,
including an association with clinical presentation and severity of the disease.
MicroRNAs are modulators of the Wnt signaling pathway, indicating a novel
pathogenetic mechanism in adrenal tumorigenesis.