The rate-limiting enzyme in phosphatidylcholine synthesis regulates proliferation of the nucleoplasmic reticulum.
The nucleus contains a network of tubular invaginations of the nuclear envelope (NE), termed the nucleoplasmic reticulum (NR), implicated in transport, gene expression, and calcium homeostasis. Here, we show that proliferation of the NR, measured by the frequency of NE invaginations and tubules, is regulated by CTP:phosphocholine cytidylyltransferase-alpha (CCTalpha), the nuclear and rate-limiting enzyme in the CDP-choline pathway for phosphatidylcholine (PtdCho) synthesis. In Chinese hamster ovary (CHO)-K1 cells, fatty acids triggered activation and translocation of CCTalpha onto intranuclear tubules characteristic of the NR. This was accompanied by a twofold increase in NR tubules quantified by immunostaining for lamin A/C or the NE. CHO MT58 cells expressing a temperature-sensitive CCTalpha allele displayed reduced PtdCho synthesis and CCTalpha expression and minimal proliferation of the NR in response to oleate compared with CHO MT58 cells stably expressing CCTalpha. Expression of CCTalpha mutants in CHO58 cells revealed that both enzyme activity and membrane binding promoted NR proliferation. In support of a direct role for membrane binding in NR tubule formation, recombinant CCTalpha caused the deformation of liposomes into tubules in vitro. This demonstrates that a key nuclear enzyme in PtdCho synthesis coordinates lipid synthesis and membrane deformation to promote formation of a dynamic nuclear-cytoplasmic interface.
Lagace
Thomas A
TA
Atlantic Research Center, Departments of Pediatrics and Biochemistry and Molecular Biology, Dalhousie University, Halifax, Nova Scotia, Canada B3H 4H7.
Ridgway
Neale D
ND
D000818:Animals; D016466:CHO Cells; D002118:Calcium / Q000378:metabolism; D002384:Catalysis; D002462:Cell Membrane / Q000378:metabolism; D002467:Cell Nucleus / Q000378:metabolism*; D049109:Cell Proliferation; D056404:Chaperonin Containing TCP-1; D018833:Chaperonins; D006224:Cricetinae; D003593:Cytoplasm / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism; D005227:Fatty Acids / Q000378:metabolism; D005786:Gene Expression Regulation; D006360:Heat-Shock Proteins / Q000378:metabolism; D007700:Kinetics; D008055:Lipids / Q000737:chemistry; D008081:Liposomes / Q000737:chemistry / Q000378:metabolism; D008854:Microscopy, Electron; D008856:Microscopy, Fluorescence; D016253:Microscopy, Immunoelectron; D018832:Molecular Chaperones / Q000378:metabolism; D009154:Mutation; D019301:Oleic Acid / Q000737:chemistry; D010713:Phosphatidylcholines / Q000737:chemistry*; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry; D013696:Temperature; D013997:Time Factors
D005227:Fatty Acids; D006360:Heat-Shock Proteins; D008055:Lipids; D008081:Liposomes; D018832:Molecular Chaperones; D010713:Phosphatidylcholines; D011994:Recombinant Proteins; D019301:Oleic Acid; D056404:Chaperonin Containing TCP-1; D018833:Chaperonins; D002118:Calcium