Genomic classification of benign adrenocortical lesions.

Benign adrenal tumors cover a spectrum of lesions with distinct morphology and steroid secretion. Current classification is empirical. Beyond a few driver mutations, pathophysiology is not well understood. Here, a pangenomic characterization of benign adrenocortical tumors is proposed, aiming at unbiased classification and new pathophysiological insights. Benign adrenocortical tumors (n = 146) were analyzed by transcriptome, methylome, miRNome, chromosomal alterations and mutational status, using expression arrays, methylation arrays, miRNA sequencing, SNP arrays, and exome or targeted next-generation sequencing respectively. Pathological and hormonal data were collected for all tumors. Pangenomic analysis identifies four distinct molecular categories: (1) tumors responsible for overt Cushing, gathering distinct tumor types, sharing a common cAMP/PKA pathway activation by distinct mechanisms; (2) adenomas with mild autonomous cortisol excess and non-functioning adenomas, associated with beta-catenin mutations; (3) primary macronodular hyperplasia with ARMC5 mutations, showing an ovarian expression signature; (4) aldosterone-producing adrenocortical adenomas, apart from other benign tumors. Epigenetic alterations and steroidogenesis seem associated, including CpG island hypomethylation in tumors with no or mild cortisol secretion, miRNA patterns defining specific molecular groups, and direct regulation of steroidogenic enzyme expression by methylation. Chromosomal alterations and somatic mutations are subclonal, found in less than 2/3 of cells. New pathophysiological insights, including distinct molecular signatures supporting the difference between mild autonomous cortisol excess and overt Cushing, ARMC5 implication into the adreno-gonadal differentiation faith, and the subclonal nature of driver alterations in benign tumors, will orient future research. This first genomic classification provides a large amount of data as a starting point.

DUSP5 and DUSP6, two ERK specific phosphatases, are markers of a higher MAPK signaling activation in BRAF mutated thyroid cancers.

BACKGROUND: Molecular alterations of the MAPK pathway are frequently observed in papillary thyroid carcinomas (PTCs). It leads to a constitutive activation of the signalling pathway through an increase in MEK and ERK phosphorylation. ERK is negatively feedback-regulated by Dual Specificity Phosphatases (DUSPs), especially two ERK-specific DUSPs, DUSP5 (nuclear) and DUSP6 (cytosolic). These negative MAPK regulators may play a role in thyroid carcinogenesis. METHODS: MAPK pathway activation was analyzed in 11 human thyroid cancer cell lines. Both phosphatases were studied in three PCCL3 rat thyroid cell lines that express doxycycline inducible PTC oncogenes (RET/PTC3, H-RASV12 or BRAFV600E). Expression levels of DUSP5 and DUSP6 were quantified in 39 human PTCs. The functional role of DUSP5 and DUSP6 was investigated through their silencing in two human BRAFV600E carcinoma cell lines. RESULTS: BRAFV600E human thyroid cancer cell lines expressed higher phospho-MEK levels but not higher phospho-ERK levels. DUSP5 and DUSP6 are specifically induced by the MEK-ERK pathway in the three PTC oncogenes inducible thyroid cell lines. This negative feedback loop explains the tight regulation of p-ERK levels. DUSP5 and DUSP6 mRNA are overexpressed in human PTCs, especially in BRAFV600E mutated PTCs. DUSP5 and/or DUSP6 siRNA inactivation did not affect proliferation in two BRAFV600E mutated cell lines, which may be explained by a compensatory increase in other phosphatases. In the light of this, we observed a marked DUSP6 upregulation upon DUSP5 inactivation. Despite this, DUSP5 and DUSP6 positively control cell migration and invasion. CONCLUSIONS: Our results are in favor of a stronger activation of the MAPK pathway in BRAFV600E PTCs. DUSP5 and DUSP6 have pro-tumorigenic properties in two BRAFV600E PTC cell line models.

Dual Specificity Phosphatase 5, a Specific Negative Regulator of ERK Signaling, Is Induced by Serum Response Factor and Elk-1 Transcription Factor.

Serum stimulation of mammalian cells induces, via the MAPK pathway, the nuclear protein DUSP5 (dual-specificity phosphatase 5), which specifically interacts with and inactivates the ERK1/2 MAP kinases. However, molecular mechanisms underlying DUSP5 induction are not well known. Here, we found that the DUSP5 mRNA induction depends on a transcriptional regulation by the MAPK pathway, without any modification of the mRNA stability. Two contiguous CArG boxes that bind serum response factor (SRF) were found in a 1 Kb promoter region, as well as several E twenty-six transcription factor family binding sites (EBS). These sites potentially bind Elk-1, a transcription factor activated by ERK1/2. Using wild type or mutated DUSP5 promoter reporters, we demonstrated that SRF plays a crucial role in serum induction of DUSP5 promoter activity, the proximal CArG box being important for SRF binding in vitro and in living cells. Moreover, in vitro and in vivo binding data of Elk-1 to the same promoter region further demonstrate a role for Elk-1 in the transcriptional regulation of DUSP5. SRF and Elk-1 form a ternary complex (Elk-1-SRF-DNA) on DUSP5 promoter, consequently providing a link to an important negative feedback tightly regulating phosphorylated ERK levels.