New genes and/or molecular pathways associated with adrenal hyperplasias and related adrenocortical tumors

Abstract

Over the course of the last 10 years, we have studied the genetic and molecular mechanisms leading to disorders that affect the adrenal cortex, with emphasis on those that are developmental, hereditary and associated with adrenal hypoplasia or hyperplasia, multiple tumors and abnormalities in other endocrine glands. On the basis of this work, we propose an hypothesis on how adrenocortical tumors form and the importance of the cyclic AMP-dependent signaling pathway in this process. The regulatory subunit type 1-alpha (RIalpha) of protein kinase A (PKA) (the PRKAR1A gene) is mutated in most patients with Carney complex and primary pigmented nodular adrenocortical disease (PPNAD). Phosphodiesterase-11A (the PDE11A gene) and -8B (the PDE8B gene) mutations were found in patients with isolated adrenal hyperplasia and Cushing syndrome, as well in patients with PPNAD. PKA effects on tumor suppression and/or development and the cell cycle are becoming clear: PKA and/or cAMP act as a coordinator of growth and proliferation in the adrenal cortex. Mouse models in which the respective genes have been knocked out see m to support this notion. Genome-wide searches for other genes responsible for adrenal tumors and related diseases are ongoing; recent evidece of the involvement of the mitochondrial oxidation pathway in adrenocortical tumorigenesis is derived from our study of rare associations such as those of disorders predisposing to adrenomedullary and related tumors (Carney triad, the dyad of paragangliomas and gastric stromal sarcomas or Carney-Stratakis syndrome, hereditary leiomyomatosis and renal cancer syndrome) which appear to be associated with adrenocortical lesions.

Figure 1

Tumorigenesis in the adrenal cortex, like in other endocrine (i.e. pituitary) and non-endocrine tissues (i.e. colon) is subject to a multi-step process, although not all steps are detected in pathologic specimens, nor it is necessary for all steps to occur in all cell types. Both adenoma and cancer can form without first going through hyperplastic and adenomatous, respectively, transformation; the cAMP-signaling pathway leads to hyperplasias^{1, 2}; IGF-II overexpression (and that of other growth factors) is associated with adenomas and cancer; defects of cell cycle genes (TP53, CHEK2) are the hallmark of both sporadic and familial adrenal cancer⁸, but large benign adenomas can also harbor somatic TP53 mutations⁹. If the first “hit” is in TP53, such as is the case in LFS, cancer forms without need for any precursor steps; if, on the other hand, the first defect is in a gene of the cAMP-signaling pathway (as in CNC or MAS), the most likely outcome is hyperplasia and adenomas, which only rarely (if ever) progress to cancer. In support of this hypothesis, we and others reported somatic Wnt-signaling pathway abnormalities in adenomas formed in the context of hyperplasias^{3, 10-12}; somatic PRKAR1A mutations also occur in sporadic adenomas that behave like those in CNC. Finally, chromosomal abnormalities are common in all ADTs and their complexity progresses with the severity of the pathology^{13, 14} Abbreviations: APC = Familial polyposis coli; CNC = Carney complex; CAH = congenital adrenal hyperplasia; LFS = Li-Fraumeni syndrome; LFSv = LFS variant (TP53, CHEK2 “mild” mutations); MAS =M cCune-Albright syndrome; MEN 1 = menin - multiple endocrine neoplasia 1; PKA = protein kinase A.

Figure 2

(a) PDE11A sequence defects in patients with adrenal disease ⁴²: the upper (in red) bar shows the protein and its main PDE functional domains; the lower (in green) shows the location of the sequence defects in the 22-exon gene; R804H and R867G are relatively common polymorphisms (b) FISH on tumor cells from a single individual with iMAD and an inactivating PDE11A-sequence defect showed allelic loss (one signal) of the RP11-428I14 BAC probe containing the PDE11A gene in most cells (arrow); the ideogram of chromosome 2 and the location of the PDE11A gene on 2q31-35 are also shown to the left of the panel.

Figure 3

A. Pictures of patient CAR559.03 with Cushing syndrome ⁴³ B. Family CAR 559: the mutant allele (C) of the proband (CAR559.03) was inherited from her father (CAR559.01); her mother (CAR550.02) had normal PDE8B alleles; C. Midnight cortisol levels (in mg/dl) in patients with adrenal tumors (N=23) and control (N=7) individuals at the NIH and the levels of the proband and her father; D. Imaging and pathological findings in the proband: (1) Adrenal computed tomography (CT) of CAR 559.03; mild enlargement of both the left and right adrenal glands is present; (2) Hematoxylin and eosin staining (5x magnification) of the adrenal gland of the proband: the normal adrenocortical zonation pattern is disturbed; both nodular tissue and hyperplasia of the surrounding cortex are seen; (3) pigment in adrenocortical cells is seen by Fontana-Masson stain (40x); E. Adrenal CT of the father (CAR 559.01): (1) right and (2) left; F. The A>T substitution in patient CAR 559.03; G. Conservation of histidine (H) at position 305 of PDE8B across different species; H. In vitro expression of constructs employing the normal (wild-type or wt) and mutant (H305P) PDE8B in HEK293 cells leads to significant decrease of cAMP levels or no change, respectively, compared to the “mock” transfection; thus, the H305P mutation abolishes the ability of PDE8B to degrade cAMP.