[영문]Lipin-1 has been reported to interact with transcription factors and coactivator through its carboxy-terminal region containing LXXIL motif and to carry out transcriptional activation function. However, carboxy-terminal region (423-947), including DXDXT (active site for PAP1 activity) and LXXIL motives, did not show any transcriptional activation function in yeast and mammalian cells. In contrast, amino-terminal region (1-441) has strong transcription activation function in form of fusion protein with GAL4 DNA-binding domain. The activation domain could be delimitated from residue 217 to 399. The removal of residue 242 to 277, which is present in β isoform, did not affect the activities of its transcriptional activation function. The
transcriptional activation function of lipin-1 was enhanced by PGC-1α, but not by CBP, P/CAF, SRC-1, SRC-2 and SRC-3. In addition to transcription activation function, lipin-1 has several physiological roles in 35 skeletal muscle, which might be linked to protein-protein interactions.
For these reasons, skeletal cDNA library was screened to find out the genes showing the protein-protein interaction with lipin-1 amino-terminal region (1-327) by yeast two-hybrid system. Finally, 16 genes were revealed from 35 isolated clones. Among these genes, there are 7 cytoskeletal genes and 4 metabolic enzyme genes. The functional role of interactions with cytoskeletal proteins of lipin-1 should be addressed in
future. In metabolic enzymes, eight clones were isolated, containing the cDNA for carboxy-terminal region of PGM1. The strong binding of lipin-1 in skeletal muscle might affect the physiological activities of PGM1, resulting in changes of glucose and glycogen metabolisms. Lipin-1 can bind to ECHS1, which is one of the enzymes involved in mitochondrial fatty oxidation. The interaction with subunit J of RNA polymerase II, the ortholog of RPB11 of yeast, needs the further study in the view of the role of lipin-1 as a linker between transcriptional factors and RNA polymerase II.
The present study characterized and delimitate the activation function domain of lipin-1. I also identified the interactions of several proteins with lipin-1 amino-terminal regions and provide the important themes about their functional roles, which should be investigated.