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International audience; Several cues including pituitary adenylate cyclase-activating polypeptide (PACAP), which acts through cAMP stimulation, specify the conversion of sympathoadrenal (SA) precursors toward different cell phenotypes by promoting their survival and differentiation. Selenoprotein T (SELENOT) is a PACAP-stimulated ER oxidoreductase that exerts an essential antioxidant activity and whose up-regulation is associated with SA cell differentiation. In the present study, we investigated the transcriptional cascade elicited by PACAP/cAMP to trigger SELENOT gene transcription during the conversion of PC12 cells from SA progenitor-like cells toward a neuroendocrine phenotype. Unexpectedly, we found that PACAP/cAMP recruits the canonical pathway that regulates mitochondrial function in order to elicit SELENOT gene transcription and the consequent antioxidant response during PC12 cell differentiation. This cascade involves LKB1-mediated AMPK activation in order to stimulate SELENOT gene transcription through the PGC1-α/NRF-1 complex, thus allowing SELENOT to promote PACAP-stimulated neuroendocrine cell survival and differentiation. Our data reveal that a PACAP and cAMP-activated AMPK-PGC-1α/NRF-1 cascade is critical for the coupling of oxidative stress tolerance, via SELENOT gene expression, and mitochondrial biogenesis in order to achieve PC12 cell differentiation. The data further highlight the essential role of SELENOT in cell metabolism during differentiation.

Selenoprotein T (SelT) is a recently characterized thioredoxin-like protein whose expression is very high during development, but is confined to endocrine tissues in adulthood where its function is unknown. We report here that SelT is required for adaptation to the stressful conditions of high hormone level production in endocrine cells. Using immunofluorescence and TEM immunogold approaches, we find that SelT is expressed at the endoplasmic reticulum membrane in all hormone-producing pituitary cell types. SelT knockdown in corticotrope cells promotes unfolded protein response (UPR) and ER stress and lowers endoplasmic reticulum-associated protein degradation (ERAD) and hormone production. Using a screen in yeast for SelT-membrane protein interactions, we sort keratinocyte-associated protein 2 (KCP2), a subunit of the protein complex oligosaccharyltransferase (OST). In fact, SelT interacts not only with KCP2 but also with other subunits of the A-type OST complex which are depleted after SelT knockdown leading to POMC N-glycosylation defects. This study identifies SelT as a novel subunit of the A-type OST complex, indispensable for its integrity and for ER homeostasis, and exerting a pivotal adaptive function that allows endocrine cells to properly achieve the maturation and secretion of hormones.