Endocrine Abstracts

Mitogen-activated protein kinase (MAPK) pathway abnormalities, specifically rearrangements (RET/PTC) or activating mutations (RAS or BRAF), are highly prevalent in papillary thyroid carcinomas (PTCs). Constitutive activation of this signaling cascade causes sustained phosphorylation of extracellular signal-regulated kinase (ERK). DUSP5, which is positively regulated by ERK signaling, acts as a negative regulator of its activity. We have previously shown that DUSP5 is overexpressed in PTCs. We sought to characterize the regulation of DUSP5 expression.

We demonstrated, using pharmacological inhibitors in NIH3T3 (murine) and PC12 (rat) cell lines, that DUSP5 is an early response gene regulated by the MAPK pathway, mostly at the transcriptional level. We next focused on DUSP5 transcriptional regulation. Analysis of DUSP5 promoter region allowed us to identify two contiguous CArG Boxes, binding SRF, and several Ets responsive elements (EBS), binding Elk-1, which is positively regulated by ERK signaling. We studied in NIH3T3 the implication of these responsive elements by transient transfection of luciferase reporter genes corresponding to wild type or mutated responsive elements DUSP5 promoter (i.e. mutation of CArG Box and/or EBS). These experiments demonstrated a role for SRF and Elk-1 in the transcriptional regulation of DUSP5, confirmed by EMSA and CHIP assay. Our data indicate that the CArG Boxes play a key regulatory role in DUSP5 expression.

DUSP5 expression tracks in tandem with MAPK pathway activation. DUSP5 is regulated mainly at the transcriptional level by the transcription factors Elk1, a known target of ERK signaling and SRF. These factors can form a ternary complex (Elk1-SRF-DNA) on the DUSP5 promoter, thereby providing a link to the ERK signaling pathway. These data highlight an important feedback loop that allows a tight regulation of pERK levels.

Declaration of interest: The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project.

Funding: This work was supported, however funding details unavailable.