Alexandra Anderson

A peptide from the first fibronectin domain of NCAM acts as an inverse agonist and stimulates FGF receptor activation, neurite outgrowth and survival

Neural cell adhesion molecule (NCAM) contributes to axon growth and guidance during development and learning and memory in adulthood. Although the Ig domains mediate homophilic binding, outgrowth activity localizes to two membrane proximal fibronectin‐like domains. The first of these contains a site identified as a potential FGF receptor (FGFR) activation motif (FRM) important for NCAM stimulation of neurite outgrowth, but its activity has hitherto remained hypothetical. Here, we have tested the effects of a domain‐specific antibody and peptides corresponding to the FRM in cellular assays in vitro. The first fibronectin domain antibody inhibited NCAM‐stimulated outgrowth, indicating the importance of the domain for NCAM function. Monomeric FRM peptide behaved as an inverse agonist; low concentrations specifically inhibited neurite outgrowth stimulated by NCAM and cellular responses to FGF2, while saturating concentrations stimulated FGFR‐dependent neurite outgrowth equivalent to NCAM itself. Dendrimeric FRM peptide was 125‐fold more active and stimulated FGFR activation, FGFR‐dependent and FGF‐mimetic neurite outgrowth and cell survival (but not proliferation). We conclude that the FRM peptide contains NCAM‐mimetic bioactivity accounted for by stimulation of FGF signalling pathways at the level of or upstream from FGF receptors, and discuss the possibility that FRM comprises part of an FGFR activation site on NCAM.

Ligand concentration is a driver of divergent signaling and pleiotropic cellular responses to FGF

Fibroblast growth factors (FGFs) are soluble ligands important for embryonic patterning, limb and brain development, and stem cell proliferation. They activate specific receptors (FGFR) to elicit changes in gene expression and cellular responses such as proliferation, differentiation, and survival, but the extent to which these pleiotropic responses are driven by FGF concentration gradients has not been systematically addressed. Here, we show that a single cell type exhibits divergent, even opposing, responses to a single FGF dependent on the exposure concentration, and that this is controlled by differential signaling with specific negative feedback inhibition. Low concentrations of FGF2 stimulate survival and differentiation but actively inhibit proliferation while intermediate concentrations stimulate proliferation in the presence of serum but apoptosis in its absence. Intriguingly, high concentrations reverse the proliferation and apoptosis effects, and mirror the low concentration effects: inhibition of proliferation and stimulation of survival and differentiation. By screening for activation of sampled signaling intermediates across the FGF2 concentration range in fibroblasts, we show that the peak in proliferation and apoptosis correlates with abrupt activation of FRS‐2 and Erk that is specifically down‐regulated by high concentrations of FGF2, a pattern that contrasts with an incremental increase in activation of p38 MAP kinase and the FGFR itself, across the FGF2 concentration range. Whilst proliferation stimulated by FGF2 was dependent on p38 MAP kinase, apoptosis stimulated by proliferative concentrations of FGF2 under serum‐free conditions was, in contrast, dependent on Erk MAP kinase. These findings indicate that FGF exposure concentration precisely controls intracellular signaling and cellular responses to the growth factor, and have important implications for understanding how FGF gradients influence cell proliferation, survival, and differentiation during processes such as limb development. J. Cell. Physiol. 206: 386–393, 2006.

Synthesis and reactivity of novel γ-phosphate modified ATP analogues

We hereby present a simple yet novel chemical synthesis of a family of gamma-modified ATPs bearing functional groups on the gamma-phosphate that are amenable to further derivatization by highly selective chemical manipulations (e.g., click chemistry, Staudinger ligations). A preliminary screen of these compounds as phosphate donors with a typical wild type protein kinase (cdk2) and one of its known substrates p27(kip1) is also presented.

Synthesis and O-phosphorylation of 3,3,4,4-tetrafluoroaryl-C-nucleoside analogues

Enantioenriched tetrafluorinated aryl-C-nucleosides were synthesised in four steps from 1-benzyloxy-4-bromo-3,3,4,4-tetrafluorobutan-2-ol. The presence of the tetrafluorinated ethylene group is compatible with O-phosphorylation of the primary alcohol, as demonstrated by the successful preparation of the tetrafluorinated naphthyl-C-nucleotide.

Synthesis and reactivity of novel c-phosphate modified ATP analogues

We hereby present a simple yet novel chemical synthesis of a family of gamma-modified ATPs bearing functional groups on the gamma-phosphate that are amenable to further derivatization by highly selective chemical manipulations (e.g., click chemistry, Staudinger ligations). A preliminary screen of these compounds as phosphate donors with a typical wild type protein kinase (cdk2) and one of its known substrates p27(kip1) is also presented.

Morphoregulation by acetylcholinesterase in fibroblasts and astrocytes.

Acetylcholinesterase (AChE) terminates neurotransmission at cholinergic synapses by hydrolysing acetylcholine, but also has non‐enzymatic morphoregulatory effects on neurons such as stimulation of neurite outgrowth. It is widely expressed outside the nervous system, but its function in non‐neuronal cells is unclear. Here we have investigated the distribution and function of AChE in fibroblasts and astrocytes. We show that these cells express high levels of AChE protein that co‐migrates with recombinant AChE but contains little catalytic activity. Fibroblasts express transcripts encoding the synaptic AChE‐T isoform and its membrane anchoring peptide PRiMA‐I. AChE is strikingly distributed in arcs, rings and patches at the leading edge of spreading and migrating fibroblasts and astrocytes, close to the cell–substratum interface, and in neuronal growth cones. During in vivo healing of mouse skin, AChE becomes highly expressed in re‐epithelialising epidermal keratinocytes 1 day after wounding. AChE appears to be functionally important for polarised cell migration, since an AChE antibody reduces substratum adhesion of fibroblasts, and slows wound healing in vitro as effectively as a β1‐integrin antibody. Moreover, elevation of AChE expression increases fibroblast wound healing independently of catalytic activity. Interestingly, AChE surface patches precisely co‐localise with amyloid precursor protein and the extracellular matrix protein perlecan, but not focal adhesions or α‐dystroglycan, and contain a high concentration of tyrosine phosphorylated proteins in spreading cells. These findings suggest that cell surface AChE, possibly in a novel signalling complex containing APP and perlecan, contributes to a generalised mechanism for polarised membrane protrusion and migration in all adherent cells. J. Cell. Physiol. 215: 82–100, 2008.

A Quantitative Comparison of Wild-Type and Gatekeeper Mutant Cdk2 for Chemical Genetic Studies with ATP Analogues

Mutant kinase kinetics: Protein kinases with enlarged ATP binding sites are increasingly being used as tools to probe the functioning signal transduction cascades. Using human cyclin‐dependent kinase 2 as a model system, we demonstrate that enlargement of the ATP binding site does not substantially alter either the catalysis kinetics nor substrate or phosphorylation site selection.

The Chemoselective One-Step Alkylation and Isolation of Thiophosphorylated Cdk2 Substrates in the Presence of Native Cysteine

The elucidation of signalling pathways relies heavily upon the identification of protein kinase substrates. Recent investigations have demonstrated the efficacy of chemical genetics using ATP analogues and modified protein kinases for specific substrate labelling. Here we combine N6‐(cyclohexyl)ATPγS with an analogue‐sensitive cdk2 variant to thiophosphorylate its substrates and demonstrate a pH‐dependent, chemoselective, one‐step alkylation to facilitate the detection or isolation of thiophosphorylated peptides.

Identification of Cyclin A2 as the Downstream Effector of the Nuclear Phosphatidylinositol 4,5-Bisphosphate Signaling Network

In addition to the well characterized phosphoinositide second messengers derived from the plasma membrane, increasing evidence supports the existence of a nuclear phosphoinositide signaling network. The aim of this investigation was to dissect the role played by nuclear phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P2) in cell cycle progression and to determine the cell cycle regulatory component(s) that are involved. A number of cytosolic/nuclear PtdIns(4,5)P2-deficient Swiss 3T3 cell lines were established, and their G0/G1/S cell cycle phase transitions induced by defined mitogens were examined. Our results demonstrate that nuclear PtdIns(4,5)P2 down-regulation caused a delay in phorbol ester-induced S phase entry and that this was at least in part channeled through cyclin A2 at the transcriptional level. In summary, these data identify cyclin A2 as a downstream effector of the nuclear PtdIns(4,5)P2 signaling network and highlight the importance of nuclear PtdIns(4,5)P2 in the regulation of mammalian mitogenesis.

Cyclin D1 and Cyclin D3 Show Divergent Responses to Distinct Mitogenic Stimulation

D‐type cyclins predominantly regulate progression through the cell cycle by their interactions with cyclin‐dependent kinases (cdks). Here, we show that stimulating mitogenesis of Swiss 3T3 cells with phorbol esters or forskolin can induce divergent responses in the expression levels, localization and activation state of cyclin D1 and cyclin D3. Phorbol ester‐mediated protein kinase C stimulation induces S phase entry which is dependent on MAPK activation and increases the levels and activation of cyclin D1, whereas forskolin‐mediated cAMP‐dependent protein kinase A stimulation induces mitogenesis that is independent of MAPK, but dependent upon mTor and specifically increases the level and activation of cyclin D3. These findings uncover additional levels of complexity in the regulation of the cell cycle at the level of the D‐type cyclins and thus may have important therapeutic implications in cancers where specific D‐cyclins are overexpressed. J. Cell. Physiol. 225: 638–645, 2010.