No abstract

The p58PITSLRE is a p34 cdc2 -related protein kinase that plays an important role in normal cell cycle progression. Elevated expression of p58 PITSLRE in eukaryotic cells prevents them from undergoing normal cytokinesis and appears to delay them in late telophase. To investigate the molecular mechanism of p58 PITSLRE action, we used the yeast two-hybrid system, screened a human fetal liver cDNA library, and identified cyclin D3 as an interacting partner of p58 PITSLRE . In vitro binding assay, in vivo coimmunoprecipitation, and immunofluorescence cell staining further confirmed the association of p58 PITSLRE with cyclin D3. This binding was observed only in the G 2 /M phase but not in the G 1 /S phase of the cell cycle; meanwhile, no interaction between p110 PITSLRE and cyclin D3 was observed in all the cell cycle. The overexpression of cyclin D3 in 7721 cells leads to an exclusively accumulation of p58 PITSLRE in the nuclear region, affecting its cellular distribution. Histone H1 kinase activity of p58 PITSLRE was greatly enhanced upon interaction with cyclin D3. Furthermore, kinase activity of p58 PITSLRE was found to increase greatly in the presence of cyclin D3 using a specific substrate, ␤-1,4-galactosyltransferase 1. These data provide a new clue to our understanding of the cellular function of p58 PITSLRE and cyclin D3.

A major hurdle for harnessing small interfering RNA (siRNA) for therapeutic application is an effective and safe delivery of siRNA to target tissues and cells via systemic administration. While lipid nanoparticles (LNPs) composed of a cationic lipid, poly-(ethylene glycol) lipid and cholesterol, are effective in delivering siRNA to hepatocytes via systemic administration, they may induce multi-faceted toxicities in a dose-dependent manner, independently of target silencing. To understand the underlying mechanism of toxicities, pharmacological probes including anti-inflammation drugs and specific inhibitors blocking different pathways of innate immunity were evaluated for their abilities to mitigate LNP-siRNA-induced toxicities in rodents. Three categories of rescue effects were observed: (i) pretreatment with a Janus kinase (Jak) inhibitor or dexamethasone abrogated LNP-siRNA-mediated lethality and toxicities including cytokine induction, organ impairments, thrombocytopenia and coagulopathy without affecting siRNA-mediated gene silencing; (ii) inhibitors of PI3K, mammalian target of rapamycin (mTOR), p38 and IκB kinase (IKK)1/2 exhibited a partial alleviative effect; (iii) FK506 and etoricoxib displayed no protection. Furthermore, knockout of Jak3, tumor necrosis factor receptors (Tnfr)p55/p75, interleukin 6 (IL-6) or interferon (IFN)-γ alone was insufficient to alleviate LNP-siRNA-associated toxicities in mice. These indicate that activation of innate immune response is a primary trigger of systemic toxicities and that multiple innate immune pathways and cytokines can mediate toxic responses. Jak inhibitors are effective in mitigating LNP-siRNA-induced toxicities.

Mouse models with liver-specific expression of firefly luciferase were developed that enable a noninvasive and longitudinal assessment of small-interfering RNA (siRNA)-mediated gene silencing in hepatocytes of live animals via bioluminescence imaging. Using these models, a set of lipid nanoparticles (LNPs) with different compositions of cationic lipids, polyethylene glycol (PEG), and cholesterol, were tested for their abilities in delivering a luciferase siRNA to the liver via systemic administration. A dose-dependent luciferase knockdown by LNP/siRNA assemblies was measured by in vivo bioluminescence imaging, which correlated well with the results from parallel ex vivo analyses of luciferase mRNA and protein levels in the liver. RNA interference (RNAi)-mediated target silencing was further confirmed by the detection of RNAi-specific target mRNA cleavage. A single dose of LNP02L at 3 mg/kg (siRNA) caused 90% reduction of luciferase expression and the target repression lasted for at least 10 days. With identical components, LNPs containing 2% PEG are more potent than those with 5.4% PEG. Our results demonstrate that these liver-luciferase mouse models provide a powerful tool for a high-throughput evaluation of hepatic delivery platforms by noninvasive imaging and that the molar ratio of PEG lipid can affect the efficacy of LNPs in silencing liver targets via systemic administration.

The PITSLRE protein kinases are parts of the large family of p34cdc2-related kinases. During apoptosis induced by some stimuli, specific PITSLRE isoforms are cleaved by caspase to produce a protein that contains the C-terminal kinase domain of the PITSLRE proteins (p110C). The p110C induces apoptosis when it is ectopically expressed in Chinese hamster ovary cells. In our study, similar induction of this p110C was observed during anoikis in NIH3T3 cells. To investigate the molecular mechanism of apoptosis mediated by p110C, we used the yeast two-hybrid system to screen a human fetal liver cDNA library and identified p21-activated kinase 1 (PAK1) as an interacting partner of p110C. The association of p110C with PAK1 was further confirmed by in vitro binding assay, in vivo coimmunoprecipitation, and confocal microscope analysis. The interaction of p110C with PAK1 occurred within the residues 210 -332 of PAK1. Neither association between p58 PITSLRE or p110 PITSLRE and PAK1 nor association between p110C and PAK2 or PAK3 was observed. Anoikis was increased and PAK1 activity was inhibited when NIH3T3 cells were transfected with p110C. Furthermore, the binding of p110C with PAK1 and inhibition of PAK1 activity were also observed during anoikis. Taken together, these data suggested that PAK1 might participate in the apoptotic pathway mediated by p110C.Apoptosis is a form of altruistic cell suicide, which is involved in many physiological processes, including tissue homeostasis, embryonic development, and immune response (1, 2). It is becoming increasingly clear that cell cycle regulators such as the p34cdc2 gene family could influence apoptosis (3-7). The PITSLRE protein kinases, which are coded by the gene localized to human chromosome 1p36.3 and a syntenic region of mouse chromosome 4, are parts of the large family of p34cdc2-related kinases (8 -14). There are at least 20 PITSLRE protein kinase isoforms, which are differentially expressed in mammalian tissues and regulate diverse cellular functions, including the cell cycle control, tumorigenesis, the regulation of RNA splicing or transcription, and so on (8, 10 -11,13-26). Studies indicated that several of the PITSLRE protein kinase isoforms might serve as effectors in apoptotic signaling pathways (15-18).During apoptosis induced by Fas or tumor necrosis factor, the action of p110C, a novel processed PITSLRE isoform resulting from the proteolysis of specific larger PITSLTR isoforms, significantly increased (15,18). Previous studies of our group and others (15,26) showed that apoptosis was increased when p110C was ectopically expressed in Chinese hamster ovary cells or SMMC 7721 hepatocarcinoma cells. These data suggested that p110C might play an important role in mediating apoptosis. In this study, we also detected the expression of p110C in NIH3T3 cells during anoikis, which is a form of apoptosis induced by the disruption of cell-matrix interaction. In agreement with the previous studies, a similar induction of p110C was observed during anoikis in NIH3T3 cells. It ...