Helen R. Irving

A critical review of the role of Fc gamma receptor polymorphisms in the response to monoclonal antibodies in cancer

Antibody-dependent cellular cytotoxicity (ADCC) is a major mechanism of action of therapeutic monoclonal antibodies (mAbs) such as cetuximab, rituximab and trastuzumab. Fc gamma receptors (FcgR) on human white blood cells are an integral part of the ADCC pathway. Differential response to therapeutic mAbs has been reported to correlate with specific polymorphisms in two of these genes: FCGR2A (H131R) and FCGR3A (V158F). These polymorphisms are associated with differential affinity of the receptors for mAbs. This review critically examines the current evidence for genotyping the corresponding single nucleotide polymorphisms (SNPs) to predict response to mAbs in patients with cancer.

Impact of pyrethroid resistance on operational malaria control in Malawi

The impact of insecticide resistance on insect-borne disease programs is difficult to quantify. The possibility of eliminating malaria in high-transmission settings is heavily dependent on effective vector control reducing disease transmission rates. Pyrethroids are the dominant insecticides used for malaria control, with few options for their replacement. Their failure will adversely affect our ability to control malaria. Pyrethroid resistance has been selected in Malawi over the last 3 y in the two major malaria vectors Anopheles gambiae and Anopheles funestus, with a higher frequency of resistance in the latter. The resistance in An. funestus is metabolically based and involves the up-regulation of two duplicated P450s. The same genes confer resistance in Mozambican An. funestus, although the levels of up-regulation differ. The selection of resistance over 3 y has not increased malaria transmission, as judged by annual point prevalence surveys in 1- to 4-y-old children. This is true in areas with long-lasting insecticide-treated nets (LLINs) alone or LLINs plus pyrethroid-based insecticide residual spraying (IRS). However, in districts where IRS was scaled up, it did not produce the expected decrease in malaria prevalence. As resistance increases in frequency from this low initial level, there is the potential for vector population numbers to increase with a concomitant negative impact on control efficacy. This should be monitored carefully as part of the operational activities in country.

The Phytosulfokine (PSK) Receptor Is Capable of Guanylate Cyclase Activity and Enabling Cyclic GMP-dependent Signaling in Plants

Phytosulfokines (PSKs) are sulfated pentapeptides that stimulate plant growth and differentiation mediated by the PSK receptor (PSKR1), which is a leucine-rich repeat receptor-like kinase. We identified a putative guanylate cyclase (GC) catalytic center in PSKR1 that is embedded within the kinase domain and hypothesized that the GC works in conjunction with the kinase in downstream PSK signaling. We expressed the recombinant complete kinase (cytoplasmic) domain of AtPSKR1 and show that it has serine/threonine kinase activity using the Ser/Thr peptide 1 as a substrate with an approximate Km of 7.5 μm and Vmax of 1800 nmol min−1 mg−1 of protein. This same recombinant protein also has GC activity in vitro that is dependent on the presence of either Mg2+ or Mn2+. Overexpression of the full-length AtPSKR1 receptor in Arabidopsis leaf protoplasts raised the endogenous basal cGMP levels over 20-fold, indicating that the receptor has GC activity in vivo. In addition, PSK-α itself, but not the non-sulfated backbone, induces rapid increases in cGMP levels in protoplasts. Together these results indicate that the PSKR1 contains dual GC and kinase catalytic activities that operate in vivo and that this receptor constitutes a novel class of enzymes with overlapping catalytic domains.

Developing a model of plant hormone interactions

Plant growth and development is influenced by mutual interactions among plant hormones. The five classical plant hormones are auxins, cytokinins, gibberellins, abscisic acid and ethylene. They are small diffusible molecules that easily penetrate between cells. In addition, newer classes of plant hormones have been identified such as brassinosteroids, jasmonic acid, salicylic acid and various small proteins or peptides. These hormones also play important roles in the regulation of plant growth and development. This review begins with a brief summary of the current findings on plant hormones. Based on this knowledge, a conceptual model about interactions among plant hormones is built so as to link and develop an understanding of the diverse functions of different plant hormones as a whole in plants.

Rapid, plateau-like increases in intracellular free calcium are associated with nod-factor-induced root-hair deformation

Rhizobia excrete variously substituted lipo-oligosaccha-ride Nod factors into the legume rhizosphere. Homologous legumes respond to these signals through deformation of the root hairs and the development of nodulation foci in the root cortex. Cellular events in root hairs from the susceptible zone of nearly mature root hairs were studied in root segments loaded with the calcium indicators Fura-2 or Fluo-3. Application of 10-9 M Nod factors of the broad-host-range Rhizobium sp. NGR234 to the homologous legume Vigna unguiculata resulted, within seconds, in plateau-like increases in intracellular free calcium ([Ca2+]i) in the root hairs and root epidermal cells. Nod factors of R. meliloti at 10-9 M caused equally rapid increases in [Ca2+]i in the root hairs and epidermal cells of the nonhost V. unguiculata, and also induced root-hair deformation. The chitin tetramer, N-N′-N″-N′″-tetracetylchitotetraose, which represents the backbone of Nod factors, induced neither root-hair deformation nor changes in [Ca2+]i...

Local and systemic induction of peroxidase, chitinase and resistance in cucumber plants by K2HPO4☆

Spraying the lower surface of the first true leaf (leaf 1) of cucumber plants with 50 mm K2HPO4 induced systemic resistance to anthracnose caused by Colletotrichum lagenarium, 2 to 7 days later. Within 16 h of application, the activities of peroxidase and chitinase increased in the induced leaf, and they continued to increase over the next 7 days reaching levels at least ten-fold higher than in leaf 1 of plants treated with water. During this period, the activities of both enzymes were usually two-fold or higher in leaf 2 of plants induced with K2HPO4 than in plants treated with water. If the induced plants were not further treated or mock-challenged with water on leaf 2, the enzyme levels increased slightly and levelled out at between two or four-fold higher than in the corresponding control plants. If plants were challenged with C. lagenarium on leaf 2, the enzyme activity at the site of challenge increased in the induced plants prior to rising in the control plants. Large increases in enzyme activity were only evident after the lesions became visible (3–4 days after challenge) in the control plants and this only occurred at the site of challenge. Seven days after challenge, the enzyme activities in the leaf tissue adjacent to the site of inoculation were similar in both the control and induced plants. Correlations were made between peroxidase and chitinase activities induced by several treatments on leaf 1 and the level of protection observed in leaf 2 after challenge with C. lagenarium.

Cyclic GMP modulates stomatal opening induced by natriuretic peptides and immunoreactive analogues

Abstract In this paper we demonstrate that compounds that promote stomatal opening such as kinetin, atrial natriuretic peptide (ANP) and plant natriuretic peptide immunoanalogues (irPNP) significantly elevate cGMP in guard cell protoplasts. Stomata opened by irPNP are induced to close in the presence of the guanylate cyclase inhibitor, LY 83583. The effect of cGMP on stomatal opening appears to be linked with Ca 2+ levels. ANP, irPNP and 8-Br-cGMP all induce stomatal opening and this is inhibited by compounds that lower intracellular Ca 2+ levels such as ethylene glycol bis(β-aminoethyl ether) N,N,N’,N’ -tetraacetic acid (EGTA), ruthenium red and procaine. This connection between Ca 2+ and cGMP is further supported by the fact that irPNP induced increases in cGMP levels do not occur in the presence of EGTA. Since the plasma membrane H + -ATPase is a key enzyme driving stomatal opening, we determined if a causal relationship exists between cGMP, ANP or irPNP and proton transport across the guard cell. Our results showed that the activity of the H + -ATPase is reduced by 8-Br-cGMP and increased by ANP and irPNP. However, ATP-dependent transmembrane H + gradients are only increased with ANP and not irPNP. This irPNP response can be explained by a direct or indirect irPNP-dependent activation of the enzyme that does not translate into an increase in proton gradient, possibly because irPNP affects H + coupled symporters.

The Effect of Cations on Zoospores of the Fungus Phytophthora cinnamomi

Summary: Swimming zoospores of the fungus Phytophthora cinnamomi exposed to a range of ions were much more sensitive to cations than anions. One cation, Ca2+, induced zoospores to encyst and subsequently germinate, but most cations induced encystment only and were toxic at higher concentrations. In general, the sensitivity of zoospores to a cation increased with its charge density. At 0.3 μm, La3+reduced the viability of a zoospore population to 50%, while Fe3+(20 μm) and Mn2+(50 μm) induced encystment with only a slight decrease in viability. The other divalent and monovalent cations tested (Mg2+, Ca2+, Ba2+, Li+, Na+, K+, Cs+, NH4 +) were effective in inducing encystment or reducing viability at higher concentrations. Each ion showed a distinctive concentration–response curve. Only F−and CH3COO−among the anions tested (Cl−, NO3 −, F−, H2PO4 2-, SO4 2-, CH3COO−) had any effect on zoospores, and at 20 mM (pH 6.0) they reduced viability. The cysts (cystospores) of the fungus were generally less sensitive to cations than were swimming zoospores, and only Cs+and K+(50 mM) reduced viability to the same extent in each population. Both zoospores and cysts of this fungus had a broad tolerance to pH and temperature, but cysts were more resistant to low temperatures than were motile zoospores.

Identification of neurons that express 5-hydroxytryptamine4 receptors in intestine

Abstract5-Hydroxytryptamine (5-HT) is an endogenous stimulant of intestinal propulsive reflexes. It exerts its effects partly through 5-HT4 receptors; 5-HT4 receptor agonists that are stimulants of intestinal transit are in clinical use. Both pharmacological and recent immunohistochemical studies indicate that 5-HT4 receptors are present on enteric neurons but the specific neurons that express the receptors have not been determined. In the present work, we describe the characterization of an anti-5-HT4 receptor antiserum that reveals immunoreactivity for enteric neurons and other cell types in the gastrointestinal tract. With this antiserum, 5-HT4 receptor immunoreactivity has been found in the muscularis mucosae of the rat oesophagus, a standard assay tissue for 5-HT4 receptors. It is also present in the muscularis mucosae of the guinea-pig and mouse oesophagus. In guinea-pig small intestine and rat and mouse colon, 5-HT4 receptor immunoreactivity occurs in subpopulations of enteric neurons, including prominent large neurons. Double-staining has shown that these large neurons in the guinea-pig small intestine are also immunoreactive for two markers of intrinsic primary afferent neurons, cytoplasmic NeuN and calbindin. Some muscle motor neurons in the myenteric ganglia are immunoreactive for this receptor, whereas it is rarely expressed by secretomotor neurons. Immunoreactivity also occurs in the interstitial cells of Cajal but is faint in the external muscle. Expression of the protein and mRNA has been confirmed in extracts containing enteric neurons. The observations suggest that one site of action of 5-HT4 receptor agonists is the intrinsic primary afferent neurons.

An immunoaffinity purified plant natriuretic peptide analogue modulates cGMP levels in the Zea mays root stele

Natriuretic peptides (NPs) are a family of peptide hormones strongly implicated in the regulation of salt and water homeostasis in vertebrates. Recently, evidence has been presented for the presence of a NP hormone system in plants. Atrial natriuretic peptide (ANP) bound specifically to isolated leaf membranes and promoted stomatal opening in a concentration and conformation dependent manner. We have immunoaffinity purified biologically active plant NP analogues from Hedera helix (ivy). Here we report that one of these immunoreactive plant NP fractions rapidly and specifically increases cyclic guanosine-3%,5%-monophosphate (cGMP) levels in stele tissue isolated from maize roots within 30 s. ANP and kinetin do not affect cGMP levels in maize root stele tissue. Moreover LY 83583 an inhibitor of guanylate cyclase does not affect any of these responses. Since LY 83583 does not always inhibit particulate guanylate cyclase, these results support the existence of a membrane bound PNP receptor containing intrinsic guanylate cyclase activity analogous to animal NP receptors. We postulate the presence of biologically active PNP system in the stele and speculate that it modulates solute movements in and out of this tissue.