Abstract
Various molecular and cellular alterations of the cyclic adenosine monophosphate (cAMP)
pathway have been observed in endocrine tumors. Since protein kinase A (PKA) is a
central key component of the cAMP pathway, studies of the alterations of PKA subunits
in endocrine tumors reveal new aspects of the mechanisms of cAMP pathway alterations
in human diseases. So far, most alterations have been observed for the regulatory
subunits, mainly PRKAR1A and to a lower extent, PRKAR2B. One of the best examples of such alteration today is the multiple neoplasia syndrome
Carney complex (CNC). The most common endocrine gland manifestations of CNC are pituitary
GH-secreting adenomas, thyroid tumors, testicular tumors, and ACTH-independent Cushing’s
syndrome due to primary pigmented nodular adrenocortical disease (PPNAD). Heterozygous
germline inactivating mutations of the PKA regulatory subunit RIα gene (PRKAR1A) are observed in about two-third of CNC patients, and also in patients with isolated
PPNAD. PRKAR1A is considered as a tumor suppressor gene. Interestingly, these mutations can also
be observed as somatic alterations in sporadic endocrine tumors. More than 120 different
PRKAR1A mutations have been found today. Most of them lead to an unstable mutant mRNA, which
will be degraded by nonsense mediated mRNA decay. In vitro and in vivo functional
studies are in progress to understand the mechanisms of endocrine tumor development
due to PKA regulatory subunits inactivation. PRKAR1A mutations stimulate in most models PKA activity, mimicking in some way cAMP pathway
constitutive activation. Cross-talks with other signaling pathways summarized in this
review have been described and might participate in endocrine tumorigenesis.
Key words
cAMP - PKA - adrenal tumors - pituitary tumors