The rate-limiting enzyme in phosphatidylcholine synthesis is associated with nuclear speckles under stress conditions

• Published in: Biochimica et biophysica acta Vol. 1801; no. 11; pp. 1184 - 1194
• Main Authors: Favale, Nicolás O., Fernández-Tome, María C., Pescio, Lucila G., Sterin-Speziale, Norma B.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.11.2010
• Subjects: Animals; Cell Line; Cell Nucleus - metabolism; Choline-Phosphate Cytidylyltransferase - chemistry; Choline-Phosphate Cytidylyltransferase - physiology; CTP:Phosphocholine Cytidylyltransferase; Cytoplasm - metabolism; Dogs; Endoplasmic Reticulum - metabolism; Enzymes - chemistry; Gene Silencing; Hypertonic stress; Lamin Type A - chemistry; Microscopy, Confocal - methods; Microscopy, Fluorescence - methods; Nuclear organization; Phosphatidylcholines - biosynthesis; Protein Transport; Speckle; Time Factors; NR; CCT; Nuclear organization; Speckle; Hypertonic stress; TOTO-3; CTP:Phosphocholine Cytidylyltransferase; ER; DIC
• ISSN: 1388-1981; 0006-3002; 1879-2618
• DOI: 10.1016/j.bbalip.2010.07.003

Phosphatidylcholine (PtdCho) is the most abundant phospholipid in eukaryotic membranes and its biosynthetic pathway is generally controlled by CTP:Phosphocholine Cytidylyltransferase (CCT), which is considered the rate-limiting enzyme. CCT is an amphitropic protein, whose enzymatic activity is commonly associated with endoplasmic reticulum (ER) translocation; however, most of the enzyme is intranuclearly located. Here we demonstrate that CCTα is concentrated in the nucleoplasm of MDCK cells. Confocal immunofluorescence revealed that extracellular hypertonicity shifted the diffuse intranuclear distribution of the enzyme to intranuclear domains in a foci pattern. One population of CCTα foci colocalised and interacted with lamin A/C speckles, which also contained the pre-mRNA processing factor SC-35, and was resistant to detergent and salt extraction. The lamin A/C silencing allowed us to visualise a second more labile population of CCTα foci that consisted of lamin A/C-independent foci non-resistant to extraction. We demonstrated that CCTα translocation is not restricted to its redistribution from the nucleus to the ER and that intranuclear redistribution must thus be considered. We suggest that the intranuclear organelle distribution of CCTα is a novel mechanism for the regulation of enzyme activity. ►The induction of MDCK cell differentiation evoked by hypertonicity produces a specific intranucleoplasmic organisation of CCTα. ►CCTα distribution does not implicate the exit from the nucleus but involves intranuclear foci organisation. ►The entry of CCTα into the speckles could constitute a physiological mechanism to control CCTα activity.