Thyroid Hormones Induce Sumoylation of the Cold Shock Domain-Containing Protein PIPPin in Developing Rat Brain and in Cultured Neurons

We previously identified a cold shock domain (CSD)-containing protein (PIPPin), expressed at high level in brain cells. PIPPin has the potential to undergo different posttranslational modifications and might be a good candidate to regulate the synthesis of specific proteins in response to extracellular stimuli. Here we report the effects of T3 on PIPPin expression in developing rat brain. We found that a significant difference among euthyroid and hypothyroid newborn rats concerns sumoylation of nuclear PIPPin, which is abolished by hypothyroidism. Moreover, T3 dependence of PIPPin sumoylation has been confirmed in cortical neurons purified from brain cortices and cultured in a chemically defined medium (Maat medium), with or without T3. We also report that about one half of unmodified as well as all the sumoylated form of PIPPin could be extracted from nuclei with HCl, together with histones. Moreover, this HCl-soluble fraction remains in the nucleus even after treatment with 0.6 m KCl, thus suggesting strong interaction of PIPPin with nuclear structures and perhaps chromatin.