Phosphoinositide signaling regulates all eukaryotic cells. In the phosphoinositide cycle, phosphatidylinositol (PI) is sequentially phosphorylated on the fourth and fifth hydroxyl of the myo-inositol ring by PI kinases and then phosphatidylinositol-phosphate kinases (PIPKs), forming phosphatidylinositol-4,5-bisphosphate (PIP2). PIP2 is a direct lipid messenger for many cellular responses and is an essential precursor to many other phosphatidylinositol-derived second messengers. Remarkably phosphoinositide signaling occurs within the nucleus where PIP2 is spatially generated at structures called nuclear speckles. Speckles have no identified membrane, but contain proteins and enzymes with roles in mRNA processing. PIPKs signal by interacting with effectors of the PIPn that they generate. PIPKI? is an isoform that makes PIP2 that is present in the nucleus at speckles. PIP2 is also generated at speckles and may regulate activities of mRNA processing enzymes. In this context, we have discovered that PIPKI? interacts with a novel poly A polymerase (PAP) now called Star-PAP. Star-PAP is dramatically and specifically stimulated by PIP2. Star-PAP and PIPKI? are regulated by oxidative stress response and this regulates the expression of stress response mRNAs, including heme oxygenase-1 (HO-1), apolipoprotein E (APOE) and NAD(P)H:quinone oxidoreductase (NQO1). We hypothesize that PIPKI? and Star-PAP function as a polyadenylation complex that associates with the transcriptional machinery required for 3'-processing of pre-mRNA transcripts. This novel polyadenylation complex is uniquely regulated by phosphoinositide signals and is required in vivo for 3'- processing of select mRNA transcripts, resulting in a novel mechanism to regulate gene expression. We will test this hypothesis with the following focused specific aims: 1. Study enzymatic activity of Star- PAP and regulation by phosphoinositides. Functional domains in Star-PAP that modulate specificity toward RNA substrates will be revealed. 2. Characterize Star-PAP complex assembly down stream of oxidative stress signals. The role of functional domains in Star-PAP will be defined. 3. The mechanisms for Star-PAP regulation of mRNAs in vivo will be investigated with an emphasis on the interaction with genes and mRNAs. It will be determined if the poly(A) tail generated by Star-PAP different than that by canonical PAP. The regulation of expression of the stress response proteins HO-1, APOE, and NQO1 play key biological roles that have dramatic implications for many aspects of human health including cardiovascular disease, transplantation, neurodegeneration and stroke, cancer therapy, and pulmonary medicine. The regulation of pre-mRNA polyadenylation by phosphoinositide signals via PIPKI? and Star-PAP is an incredibly novel finding that has many implications for nuclear signal transduction and gene expression.
The expression of cellular proteins from genes occurs through messenger RNAs (mRNAs) made by each gene and this requires that the mRNA have a polyadenosine tail. This tail is required before the mRNA can make cellular proteins. We have discovered a new enzyme that uniquely makes these tails and this enzyme works to generate mRNAs and the encoded proteins. Most interesting and paradigm shifting is the fact that this process is regulated by a lipid messenger called phosphatidylinositol-4,5-bisphosphate. The genes whose expression this novel pathway controls are heme oxygenase-1 (HO-1), apolipoprotein E (APOE) and NAD(P)H:quinone oxidoreductase (NQO1). The control of these genes has dramatic implications for many aspects of human health including cardiovascular disease, transplantation, neurodegeneration, cancer therapy, and pulmonary medicine.
|Li, W; Anderson, R A (2014) Star-PAP controls HPV E6 regulation of p53 and sensitizes cells to VP-16. Oncogene 33:928-32|
|Li, Weimin; Laishram, Rakesh S; Anderson, Richard A (2013) The novel poly(A) polymerase Star-PAP is a signal-regulated switch at the 3'-end of mRNAs. Adv Biol Regul 53:64-76|
|Li, Weimin; Laishram, Rakesh S; Ji, Zhe et al. (2012) Star-PAP control of BIK expression and apoptosis is regulated by nuclear PIPKI* and PKCýý signaling. Mol Cell 45:25-37|
|Schramp, Mark; Thapa, Narendra; Heck, Jessica et al. (2011) PIPKI? regulates ?-catenin transcriptional activity downstream of growth factor receptor signaling. Cancer Res 71:1282-91|
|Laishram, Rakesh S; Barlow, Christy A; Anderson, Richard A (2011) CKI isoforms ýý and ýý regulate Star-PAP target messages by controlling Star-PAP poly(A) polymerase activity and phosphoinositide stimulation. Nucleic Acids Res 39:7961-73|
|Barlow, Christy A; Laishram, Rakesh S; Anderson, Richard A (2010) Nuclear phosphoinositides: a signaling enigma wrapped in a compartmental conundrum. Trends Cell Biol 20:25-35|
|Heck, Jessica N; Mellman, David L; Ling, Kun et al. (2007) A conspicuous connection: structure defines function for the phosphatidylinositol-phosphate kinase family. Crit Rev Biochem Mol Biol 42:15-39|
|Ling, Kun; Schill, Nicholas J; Wagoner, Matthew P et al. (2006) Movin' on up: the role of PtdIns(4,5)P(2) in cell migration. Trends Cell Biol 16:276-84|
|Burden, L M; Rao, V D; Murray, D et al. (1999) The flattened face of type II beta phosphatidylinositol phosphate kinase binds acidic phospholipid membranes. Biochemistry 38:15141-9|
|Boronenkov, I V; Loijens, J C; Umeda, M et al. (1998) Phosphoinositide signaling pathways in nuclei are associated with nuclear speckles containing pre-mRNA processing factors. Mol Biol Cell 9:3547-60|
Showing the most recent 10 out of 19 publications