PIKE GTPase-mediated nuclear signalings promote cell survival

Decoding how receptor tyrosine kinases (RTKs) mediate nuclear calcium signaling

Calcium (Ca2+) is a highly versatile intracellular messenger that regulates several cellular processes. Although it is unclear how a single-second messenger coordinates various effects within a cell, there is growing evidence that spatial patterns of Ca2+ signals play an essential role in determining their specificity. Ca2+ signaling patterns can differ in various cell regions, and Ca2+ signals in the nuclear and cytoplasmic compartments have been observed to occur independently. The initiation and function of Ca2+ signaling within the nucleus are not yet fully understood. Receptor tyrosine kinases (RTKs) induce Ca2+ signaling resulting from phosphatidylinositol 4,5-bisphosphate (PIP2) hydrolysis and inositol 1,4,5-trisphosphate (InsP3) formation within the nucleus. This signaling mechanism may be responsible for the effects of specific growth factors on cell proliferation and gene transcription. This review highlights the recent advances in RTK trafficking to the nucleus and explains how these receptors initiate nuclear calcium signaling.

Nuclear and mitochondrial signalling Akts in cardiomyocytes

Biological actions resulting from phosphoinositide synthesis trigger multiple downstream signalling cascades by recruiting proteins with pleckstrin homology domains, including phosphoinositide-dependent kinase-1 and protein kinase B (also known as Akt). Retrospectively, more attention has been focused on the plasma membrane-associated interactions of these molecules and resulting cytoplasmic target activation. The complex biological activities exerted by Akt activation suggest, however, that more subtle and complex subcellular control mechanisms are involved. This review examines the regulation of Akt activity from the perspective of subcellular compartmentalization and focuses specifically upon the actions of Akt activation downstream from phosphoinositide synthesis that influence cell biology by altering nuclear signalling leading to Pim-1 kinase induction as well as hexokinase phosphorylation that, together with Akt, serves to preserve mitochondrial integrity.

NGF and its receptors TrkA and p75NTR in the epithelium of oral lichen

BACKGROUND

Nerve growth factor (NGF) can through its receptors TrkA and p75(NTR) convey signals for cell survival, differentiation and death. The aim of this study was to examine whether NGF can play a role in the pathology of oral lichen (OL).

METHODS

Sections from biopsies taken from patients with erythematous (ERY) OL and from volunteers with normal oral mucosa (NOM) were immunostained with antibodies against NGF, proNGF, TrkA, phosphorylated Trk, p75(NTR) and phosphorylated Akt (pAkt) and expression of RNA coding for proNGF/NGF was investigated by in situ hybridization.

RESULTS

Both in ERY OL and NOM, cytoplasmic staining for NGF was seen in granular and upper spinous cell layers of the epithelium, whereas proNGF staining was seen in all epithelial cell layers. In situ hybridization showed that the proNGF protein was produced in the same cell layers. In OL, strong cytoplasmic stainings for TrkA and activated Trk (pTrk) were observed in all epithelial cell layers while these stainings were only weak in NOM. Basal keratinocytes in OL showed no or only weak cytoplasmic staining for p75(NTR), but in NOM there was a clear cell membrane staining. In OL, strong cytoplasmic and intermittent nuclear staining for pAkt was observed in spinous, granular and superficial layers, while basal and parabasal keratinocytes were negative. This staining was weak or absent in the entire epithelium of NOM.

CONCLUSIONS

TrkA upregulation and activation in OL is one of the pathways that can activate pAkt and thereby rescue epithelial cells from untimely cell death.

Contribution of AZAP-Type Arf GAPs to cancer cell migration and invasion

Arf GAPs are a family of proteins with a common catalytic domain that induces hydrolysis of GTP bound to the small GTP-binding protein Arf. The proteins are otherwise structurally diverse. Several subtypes of Arf GAPs have been found to be targets of oncogenes and to control cell proliferation and cell migration. The latter effects are thought to be mediated by coordinating changes in actin remodeling and membrane traffic. In this chapter, we discuss Arf GAPs that have been linked to oncogenesis and the molecular mechanisms underlying the effects of these proteins in cancer cells. We also discuss the enzymology of the Arf GAPs related to possible targeted inhibition of specific subtypes of Arf GAPs.

Localization of agonist-sensitive PtdIns(3,4,5)P3 reveals a nuclear pool that is insensitive to PTEN expression

Phosphatidylinositol (3,4,5) trisphosphate [PtdIns(3,4,5)P3] is a lipid second messenger, produced by Type I phosphoinositide 3-kinases (PI 3-kinases), which mediates intracellular responses to many growth factors. Although PI 3-kinases are implicated in events at both the plasma membrane and intracellular sites, including the nucleus, direct evidence for the occurrence of PtdIns(3,4,5)P3 at non-plasma membrane locations is limited. We made use of the pleckstrin homology (PH) domain of general receptor for phosphoinositides (Grp1) to detect PtdIns(3,4,5)P3 in an on-section labeling approach by quantitative immunogold electron microscopy. Swiss 3T3 cells contained low levels of PtdIns(3,4,5)P3 that increased up to 15-fold upon stimulation with platelet-derived growth factor (PDGF). The signal was sensitive to PI 3-kinase inhibitors and present mainly at plasma membranes, including lamellipodia, and in a surprisingly large pool within the nuclear matrix. Comparatively little labeling was observed in endomembranes. A similar distribution of PtdIns(3,4,5)P3 was observed in U87MG cells, which lack the PtdIns(3,4,5)P3 phosphatase, PTEN. Re-expression of PTEN into U87MG cells ablated plasma membrane PtdIns(3,4,5)P3, but not the nuclear pool of this lipid even when PTEN was targeted to nuclei. These data have important implications for the versatility of PI 3-kinase signaling and for the proposed functions of PTEN in the nucleus.