Insulin’s metabolic effects in the liver are widely appreciated, but insulin’s ability to act as a hepatic mitogen is less well understood. Because the Insulin Receptor (IR) can traffic to the nucleus, and calcium (Ca2+) signals within the nucleus regulate cell proliferation, we investigated whether insulin’s mitogenic effects result from activation of Ca2+ signaling pathways by IRs within the nucleus. Insulin-induced increases in Ca2+ and cell proliferation depended upon clathrin- and caveolin-dependent translocation of the IR to the nucleus, as well as upon formation of inositol 1,4,5,-trisphosphate (InsP3) in the nucleus, whereas insulin’s metabolic effects did not depend on either of these events. Moreover, liver regeneration after partial hepatectomy also depended upon formation of InsP3 in the nucleus but not the cytosol, whereas hepatic glucose metabolism was not affected by buffering InsP3 in the nucleus. Conclusion: These findings provide evidence that insulin’s mitogenic effects are mediated by a subpopulation of IRs that traffic to the nucleus to locally activate InsP3-dependent Ca2+ signaling pathways. The steps along this signaling pathway reveal a number of potential targets for therapeutic modulation of liver growth in health and disease.

Although used in medical applications for centuries, the development of nanotechnology has shed new light in the plethora of possible medical and biological applications using gold-based nanostructures. Gold nanostructures are stable and relatively inert in biological systems, leading to low reatogenicity, biocompatibility and general lack of toxicity. Allied to that, gold nanoparticles present optical and electronic properties that have been exploited in a range of biomedical applications. In this review we discuss biologically relevant properties of gold nanoparticles and how they are used in some biomedicine fields, especially those involving biosensing of biological analytes – including viruses and antibodies against them, cancer therapies, and antigen delivery, including viral antigens – as part of nonclassic vaccine strategies.

Calcium (Ca2+) is an essential signal transduction element involved in the regulation of several cellular activities and it is required at various key stages of the cell cycle. Intracellular Ca2+ is crucial for the orderly cell cycle progression and plays a vital role in the regulation of cell proliferation. Recently, it was demonstrated by in vitro and in vivo studies that nucleoplasmic Ca2+ regulates cell growth. Even though the mechanism by which nuclear Ca2+ regulates cell proliferation is not completely understood, there are reports demonstrating that activation of tyrosine kinase receptors (RTKs) leads to translocation of RTKs to the nucleus to generate localized nuclear Ca2+ signaling which are believed to modulate cell proliferation. Moreover, nuclear Ca2+ regulates the expression of genes involved in cell growth. This review will describe the nuclear Ca2+ signaling machinery and its role in cell proliferation. Additionally, the potential role of nuclear Ca2+ as a target in cancer therapy will be discussed.

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BackgroundAdenosine triphosphate (ATP) is secreted from hepatocytes under physiological conditions and plays an important role in liver biology through the activation of P2 receptors. Conversely, higher extracellular ATP concentrations, as observed during necrosis, trigger inflammatory responses that contribute to the progression of liver injury. Impaired calcium (Ca2+) homeostasis is a hallmark of acetaminophen (APAP)-induced hepatotoxicity, and since ATP induces mobilization of the intracellular Ca2+ stocks, we evaluated if the release of ATP during APAP-induced necrosis could directly contribute to hepatocyte death.ResultsAPAP overdose resulted in liver necrosis, massive neutrophil infiltration and large non-perfused areas, as well as remote lung inflammation. In the liver, these effects were significantly abrogated after ATP metabolism by apyrase or P2X receptors blockage, but none of the treatments prevented remote lung inflammation, suggesting a confined local contribution of purinergic signaling into liver environment. In vitro, APAP administration to primary mouse hepatocytes and also HepG2 cells caused cell death in a dose-dependent manner. Interestingly, exposure of HepG2 cells to APAP elicited significant release of ATP to the supernatant in levels that were high enough to promote direct cytotoxicity to healthy primary hepatocytes or HepG2 cells. In agreement to our in vivo results, apyrase treatment or blockage of P2 receptors reduced APAP cytotoxicity. Likewise, ATP exposure caused significant higher intracellular Ca2+ signal in APAP-treated primary hepatocytes, which was reproduced in HepG2 cells. Quantitative real time PCR showed that APAP-challenged HepG2 cells expressed higher levels of several purinergic receptors, which may explain the hypersensitivity to extracellular ATP. This phenotype was confirmed in humans analyzing liver biopsies from patients diagnosed with acute hepatic failure.ConclusionWe suggest that under pathological conditions, ATP may act not only an immune system activator, but also as a paracrine direct cytotoxic DAMP through the dysregulation of Ca2+ homeostasis.

Subcellular Ca2+ signals control a variety of responses in the liver. For example, mitochondrial Ca2+ regulates apoptosis while Ca2+ in the nucleus regulates cell proliferation. Since apoptosis and cell growth can be related, we investigated whether mitochondrial Ca2+ also affects liver regeneration. The Ca2+ buffering protein, Parvalbumin (PV), targeted to the mitochondrial matrix and fused to green fluorescent protein (PV-MITO-GFP) was expressed in the SKHep1 liver cell line. This construct properly localized to and effectively buffered Ca2+ signals in the mitochondrial matrix. Additionally, expression of PV-MITO-GFP reduced apoptosis induced by both the intrinsic and extrinsic pathways. The reduction in cell death correlated with increased expression of anti-apoptotic genes bcl-2, mcl-1, and bcl-xL, and decreased expression of the pro-apoptotic genes p53, bax, apaf-1 and caspase-6. PV-MITO-GFP was also expressed in hepatocytes in vivo using an adenoviral delivery system. Buffering mitochondrial Ca2+ in hepatocytes accelerated liver regeneration after partial hepatectomy, an effect that was associated with increased expression of Bcl-2 and decreased expression of Bax. Conclusion Together, these results reveal an essential role for mitochondrial Ca2+ in hepatocyte proliferation and liver regeneration, which may be mediated by regulating apoptosis.

Calcium (Ca(2+)) is an important multifaceted second messenger that regulates a wide range of cellular events. A Ca(2+)-signaling toolkit has been shown to exist in the nucleus and to be capable of generating and modulating nucleoplasmic Ca(2+) transients. Within the nucleus, Ca(2+) controls cellular events that are different from those modulated by cytosolic Ca(2+). This review focuses on nuclear Ca(2+) signals and their role in regulating physiological and pathological processes.

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