Endoplasmic reticulum stress induction of the Grp78/BiP promoter: activating mechanisms mediated by YY1 and its interactive chromatin modifiers.

The unfolded protein response is an evolutionarily conserved mechanism whereby cells respond to stress conditions that target the endoplasmic reticulum (ER). The transcriptional activation of the promoter of GRP78/BiP, a prosurvival ER chaperone, has been used extensively as an indicator of the onset of the UPR. YY1, a constitutively expressed multifunctional transcription factor, activates the Grp78 promoter only under ER stress conditions. Previously, in vivo footprinting analysis revealed that the YY1 binding site of the ER stress response element of the Grp78 promoter exhibits ER stress-induced changes in occupancy. Toward understanding the underlying mechanisms of these unique phenomena, we performed chromatin immunoprecipitation analyses, revealing that YY1 only occupies the Grp78 promoter upon ER stress and is mediated in part by the nuclear form of ATF6. We show that YY1 is an essential coactivator of ATF6 and uncover their specific interactive domains. Using small interfering RNA against YY1 and insertional mutation of the gene encoding ATF6alpha, we provide direct evidence that YY1 and ATF6 are required for optimal stress induction of Grp78. We also discovered enhancement of the ER-stressed induction of the Grp78 promoter through the interaction of YY1 with the arginine methyltransferase PRMT1 and evidence of its action through methylation of the arginine 3 residue on histone H4. Furthermore, we detected ER stress-induced binding of the histone acetyltransferase p300 to the Grp78 promoter and histone H4 acetylation. A model for the ER stress-mediated transcription factor binding and chromatin modifications at the Grp78 promoter leading to its activation is proposed.

Defining the importance of phosphatidylserine synthase 2 in mice.

Phosphatidylserine synthase 1 (Pss1) and phosphatidylserine synthase 2 (Pss2) produce phosphatidylserine by exchanging serine for the head groups of other phospholipids. Pss1 and Pss2 are structurally similar (approximately 32% amino acid identity) but differ in their substrate specificities, with Pss1 using phosphatidylcholine for the serine exchange reaction and Pss2 using phosphatidylethanolamine. Whether Pss1 and Pss2 are both required for mammalian growth and development is not known, and no data exist on the relative contributions of the two enzymes to serine exchange activities in different tissues. To address those issues and also to define the cell type-specific expression of Pss2, we generated Pss2-deficient mice in which a beta-galactosidase marker is expressed from Pss2 regulatory sequences. Histologic studies of Pss2-deficient mice revealed very high levels of beta-galactosidase expression in Sertoli cells of the testis and high levels of expression in brown fat, neurons, and myometrium. The ability of testis extracts from Pss2-deficient mice to catalyze serine exchange was reduced by more than 95%; reductions of approximately 90% were noted in the brain and liver. However, we found no perturbations in the phospholipid content of any of these tissues. As judged by Northern blots, the expression of Pss1 was not up-regulated in Pss2-deficient cells and tissues. Testis weight was reduced in Pss2-deficient mice, and some of the male mice were infertile. We conclude that Pss2 is responsible for the majority of serine exchange activity in in vitro assays, but a deficiency in this enzyme does not cause perturbations in phospholipid content or severe developmental abnormalities.