The Rate-limiting Enzyme in Phosphatidylcholine Synthesis is Associated with Nuclear Speckes under Stress Conditions

N.O. FAVALE,; NORMA STERIN-SPEZIALE; MARIA C. FERNÁNDEZ TOME

BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR AND CELL BIOLOGY OF LIPIDS

ELSEVIER SCIENCE BV

Año: 2010 vol. 1801 p. 1184 - 1194

1388-1981

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 CCTá 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 CCTá 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 CCTá foci that consisted of lamin A/C-independent foci non-resistant to extraction. We demonstrated that CCTá 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 CCTá is a novel mechanism for the regulation of enzyme activity.