Star-PAP Control of BIK Expression and Apoptosis Is Regulated by Nuclear PIPKIα and PKCδ Signaling

Abstract

SUMMARY BIK protein is an initiator of mitochondrial apoptosis and BIK expression is induced by pro-apoptotic signals including DNA damage. Here we demonstrate that 3′-end processing and expression of BIK mRNA are controlled by the nuclear PI4,5P2-regulated poly(A) polymerase Star-PAP downstream of DNA damage. Nuclear PKCδ is a key mediator of apoptosis and DNA damage stimulates PKCδ association with the Star-PAP complex where PKCδ is required for Star-PAP-dependent BIK expression. PKCδ binds the PI4,5P2-generating enzyme PIPKIα, which is essential for PKCδ interaction with the Star-PAP complex and PKCδ activity is directly stimulated by PI4,5P2. Features in the BIK 3′-UTR uniquely define Star-PAP specificity and may block canonical PAP activity toward BIK mRNA. This reveals a nuclear phosphoinositide signaling nexus where PIPKIα, PI4,5P2 and PKCδ regulate Star-PAP control of BIK expression and induction of apoptosis. This pathway is distinct from the Star-PAP-mediated oxidative stress pathway indicating signal-specific regulation of mRNA 3′-end processing.

Phosphatidylinositol-4-phosphate 5-Kinase Isoforms Exhibit Acyl Chain Selectivity for Both Substrate and Lipid Activator

“…The mutants of c-Myc-PIP5K␣ were designed using the QuikChange Lightning Kit (Stratagene, La Jolla, CA) according to the instructions of the manufacturer. FLAG-PIP5K␣ D322A expression vector (which corresponds to the human form of the enzyme) was prepared and tested as described previously (25)(26)(27). The presence of the desired mutations was verified by sequencing analysis.…”

“…The presence of a saturated acyl chain at the sn-1 position of PA considerably lowers the extent of activation. PIP5Ks have been implicated in a variety of distinct cellular processes, such as polarized trafficking of integrins (31) and regulation of polyadenylation of mRNAs (26,32). It also has been suggested that different PIP5K isoforms may regulate endocytosis of different types of cargo (33).…”

“…For example, PIP5K isoforms modulate endocytosis, exocytosis, and endosomal sorting on dis- tinct membrane compartments (19,31). The PIP5K␣ also localizes in the nucleus to modulate polyadenylation of mRNA, and this process occurs within undefined lipid complexes (26,32). Therefore, different isoforms of PIP5K are capable of functioning in highly diverse lipid environments.…”

Nucleotide specificity of the human terminal nucleotidyltransferase Gld2 (TUT2)

“…One group shows the U6 snRNA uridylating enzyme TUT6 (Trippe et al 2006) evolved from a parent clade composed of known and putative adenylyltransferases. The nucleotide specificity of TUT6 is, however, not restricted to snRNA uridylation, as it was additionally found to adenylate selected mRNAs (Mellman et al 2008;Li et al 2012). TUT6 is most closely related to the noncanonical mitochondrial poly(A) polymerase Papd1, which mediates RNA decay by polyadenylation (Bai et al 2011).…”

Multifunctional roles of PKCδ: Opportunities for targeted therapy in human disease

“…PKCδ binds to Tap63 to increase its stability and promote apoptosis (Li et al, 2015), while PKCδ targets the antiapoptotic protein, Mcl-1, for degradation to trigger apoptosis (Sitailo, Tibudan, & Denning, 2006). In addition, PKCδ has been shown to regulate 3′ end processing of BIK mRNA to induce apoptosis through a mechanism that requires the Star-PAP processing complex and nuclear PIPKIα (Li et al, 2012). Finally, as discussed below, there is ample evidence that PKCδ can regulate cell survival pathways to induce apoptosis, including NF-κB, Akt and ERK (Lu, Liu, Yamaguchi, Miki, & Yoshida, 2009) as well as DNA damage-induced pathways.…”