Regulation of ethylene gas biosynthesis by the Arabidopsis ETO1 protein.

Ethylene gas is used as a hormone by plants, in which it acts as a critical growth regulator. Its synthesis is also rapidly evoked in response to a variety of biotic and abiotic stresses. The Arabidopsis ethylene-overproducer mutants eto2 and eto3 have previously been identified as having mutations in two genes, ACS5 and ACS9, respectively; these encode isozymes of 1-aminocyclopropane-1-carboxylic acid synthase (ACS), which catalyse the rate-limiting step in ethylene biosynthesis. Here we report that another ethylene-overproducer mutation, eto1, is in a gene that negatively regulates ACS activity and ethylene production. The ETO1 protein directly interacts with and inhibits the enzyme activity of full-length ACS5 but not of a truncated form of the enzyme, resulting in a marked accumulation of ACS5 protein and ethylene. Overexpression of ETO1 inhibited induction of ethylene production by the plant growth regulator cytokinin, and promoted ACS5 degradation by a proteasome-dependent pathway. ETO1 also interacts with CUL3, a constituent of ubiquitin ligase complexes in which we propose that ETO1 serves as a substrate-specific adaptor protein. ETO1 thus has a dual mechanism, inhibiting ACS enzyme activity and targeting it for protein degradation. This permits rapid modulation of the concentration of ethylene.

Massive infantile myofibromatosis of the upper lip causing airway distress in a newborn.

Infantile myofibromatosis is a rare condition characterized by benign spindle cell tumors most commonly involving the head, neck, and chest. An infant female with a prenatal diagnosis of a large facial mass was delivered via Cesarean at 34 weeks. Sparse prenatal care was received. Following delivery, the neonate was found to have an 8 cm ulcerative mass involving the upper lip and philtrum. Respiratory distress developed, and mask ventilation was difficult secondary to the size of the mass. The patient was successfully intubated after numerous attempts and then transferred to the children's hospital. Additional imaging demonstrated similar masses within bilateral iliopsoas and gluteal muscles, and her right gastrocnemius. A biopsy confirmed infantile myofibromatosis. At two weeks of life, she underwent resection with bilateral myocutaneous advancement flaps and successful extubation. She received adjuvant vinblastine and methotrexate for her pelvic and extremity disease with excellent response. We present the first case of airway distress secondary to myocutaneous myofibromatosis.

HLA-F and MHC-I Open Conformers Bind Natural Killer Cell Ig-Like Receptor KIR3DS1.

Based on previous findings supporting HLA-F as a ligand for KIR3DL2 and KIR2DS4, we investigated the potential for MHC-I open conformers (OCs) as ligands for KIR3DS1 and KIR3DL1 through interactions measured by surface plasmon resonance. These measurements showed physical binding of KIR3DS1 but not KIR3DL1 with HLA-F and other MHC-I OC while also confirming the allotype specific binding of KIR3DL1 with MHC-I peptide complex. Concordant results were obtained with biochemical pull-down from cell lines and biochemical heterodimerization experiments with recombinant proteins. In addition, surface binding of HLA-F and KIR3DS1 to native and activated NK and T cells was coincident with specific expression of the putative ligand or receptor. A functional response of KIR3DS1 was indicated by increased granule exocytosis in activated cells incubated with HLA-F bound to surfaces. The data extend a model for interaction between MHC-I open conformers and activating KIR receptors expressed during an inflammatory response, potentially contributing to communication between the innate and adaptive immune response.

Arabidopsis ETO1 specifically interacts with and negatively regulates type 2 1-aminocyclopropane-1-carboxylate synthases.

BACKGROUND: In Arabidopsis, ETO1 (ETHYLENE-OVERPRODUCER1) is a negative regulator of ethylene evolution by interacting with AtACS5, an isoform of the rate-limiting enzyme, 1-aminocyclopropane-1-carboxylate synthases (ACC synthase or ACS), in ethylene biosynthetic pathway. ETO1 directly inhibits the enzymatic activity of AtACS5. In addition, a specific interaction between ETO1 and AtCUL3, a constituent of a new type of E3 ubiquitin ligase complex, suggests the molecular mechanism in promoting AtACS5 degradation by the proteasome-dependent pathway. Because orthologous sequences to ETO1 are found in many plant species including tomato, we transformed tomato with Arabidopsis ETO1 to evaluate its ability to suppress ethylene production in tomato fruits. RESULTS: Transgenic tomato lines that overexpress Arabidopsis ETO1 (ETO1-OE) did not show a significant delay of fruit ripening. So, we performed yeast two-hybrid assays to investigate potential heterologous interaction between ETO1 and three isozymes of ACC synthases from tomato. In the yeast two-hybrid system, ETO1 interacts with LE-ACS3 as well as AtACS5 but not with LE-ACS2 or LE-ACS4, two major isozymes whose gene expression is induced markedly in ripening fruits. According to the classification of ACC synthases, which is based on the C-terminal amino acid sequences, both LE-ACS3 and AtACS5 are categorized as type 2 isozymes and possess a consensus C-terminal sequence. In contrast, LE-ACS2 and LE-ACS4 are type 1 and type 3 isozymes, respectively, both of which do not possess this specific C-terminal sequence. Yeast two-hybrid analysis using chimeric constructs between LE-ACS2 and LE-ACS3 revealed that the type-2-ACS-specific C-terminal tail is required for interaction with ETO1. When treated with auxin to induce LE-ACS3, seedlings of ETO1-OE produced less ethylene than the wild type, despite comparable expression of the LE-ACS3 gene in the wild type. CONCLUSION: These results suggest that ETO1 family proteins specifically interact with and negatively regulate type 2 ACC synthases. Our data also show that Arabidopsis ETO1 can regulate type 2 ACS in a heterologous plant, tomato.

Odontogenic sinusitis: a case series studying diagnosis and management.

BACKGROUND: Odontogenic sinusitis is a well-recognized, but understudied form of sinusitis. Odontogenic sinusitis requires unique diagnostic criteria and a treatment regimen that differs from non-odontogenic sinusitis. The purpose of this article is to present a case series of patients with odontogenic sinusitis in order to clarify key disease characteristics and management techniques. METHODS: Retrospective case series of 55 patients with odontogenic sinusitis. Each patient underwent chart and imaging review to analyze demographic factors, diagnostic criteria, clinical course, and management. RESULTS: Fifty-five patients were identified retrospectively. Forty-four were diagnosed at initial visit. Twenty-eight (64%) of these patients were diagnosed by computed tomography (CT) scan showing dental pathology, 11 (25%) by known temporal relationship to a dental procedure, and 5 (11%) by presentation with oral-antral fistula. Only 65% of radiology reports for all patients mentioned dental pathology. Overall, 21 (38%) patients had disease resolution. Of these, 7 (33%) resolved with endoscopic sinus surgery (ESS) alone, 7 (33%) resolved with concurrent ESS and dental surgery, 2 (10%) resolved with dental surgery alone, 2 (10%) resolved with ESS after failing dental surgery, 2 (10%) resolved with medical management alone, and 1 (5%) resolved with medical management after failing dental surgery. Forty-six (84%) patients had unilateral odontogenic sinusitis. The Lund-Mackay score for all patients was (mean ± standard deviation [SD]) 4.0 ± 3.2. CONCLUSION: Odontogenic sinusitis is often misdiagnosed. Radiology reports commonly do not mention dental pathology. Management of odontogenic sinusitis needs to be tailored to each individual patient and involves varying combinations of medical management, dental surgery, and ESS.

Sympathetic neuropathy and dysphagia following doxycycline sclerotherapy.

This case report demonstrates neurologic sequela following treatment with doxycycline sclerotherapy. A six-week-old child presented with respiratory distress from a macrocystic lymphatic malformation, extending from the skull base to the anterior mediastinum. Following doxycycline sclerotherapy, the airway symptoms resolved; however, the child developed silent aspiration and Horner's syndrome. Two months following treatment the patient resumed oral diet and at one year post-intervention there has been no recurrence of symptoms, with only mild ptosis remaining. While neuropathies following doxycycline sclerotherapy have been described, aspiration has never been documented. This case demonstrates a single patient's clinical course and resolution of their neuropathies.

The ACC synthase TOE sequence is required for interaction with ETO1 family proteins and destabilization of target proteins.

The Arabidopsis ETO1 protein is a negative regulator of ethylene biosynthesis. It specifically inhibits the enzyme activity of type 2 1-aminocyclopropane-1-carboxylate synthases (ACC synthases or ACS) and promotes their degradation by a proteasome-dependent pathway. To further understand the function of the ETO1 family in the plant kingdom, we cloned a cDNA of LeEOL1 (Lycopersicon esculentum ETO 1- LIKE 1), an ETO1 homolog from tomato. LeEOL1 encodes a putative protein with domain architecture conserved in the Arabidopsis ETO1/EOL1/EOL2 proteins and in the predicted rice EOL proteins. LeEOL1 is expressed in leaf, stem, root, flower, and the full ripe stage of fruit, suggesting diverse regulatory roles in the development of tomato. Yeast two-hybrid analysis revealed specific interactions between LeEOL1 and type 2 ACC synthases. When the C-terminal 14 amino acids (TOE; target of ETO1) of LE-ACS3 specific to type 2 ACC synthases were fused to a type 1 ACS, LE-ACS2, at the corresponding position, it allowed LE-ACS2 to strongly interact with LeEOL1. A GFP-TOE(LE-ACS3) fusion protein expressed in rice calli and in the roots of wild-type Arabidopsis showed reduced stability compared to native GFP. However, the fluorescence of GFP-TOE(LE-ACS3) was comparable to that of the native GFP in Arabidopsis eto1-4 mutant. Furthermore, MG132 treatment significantly enhanced the fluorescence of GFP-TOE(LE-ACS3) in the roots of wild-type Arabidopsis. These results suggest that the ETO1-family-mediated ACS protein degradation pathway is conserved in both monocots and dicots, and that TOE acts as a protein destabilization signal recognized by the ETO1 protein family.

The POLARIS peptide of Arabidopsis regulates auxin transport and root growth via effects on ethylene signaling.

The rate and plane of cell division and anisotropic cell growth are critical for plant development and are regulated by diverse mechanisms involving several hormone signaling pathways. Little is known about peptide signaling in plant growth; however, Arabidopsis thaliana POLARIS (PLS), encoding a 36-amino acid peptide, is required for correct root growth and vascular development. Mutational analysis implicates a role for the peptide in hormone responses, but the basis of PLS action is obscure. Using the Arabidopsis root as a model to study PLS action in plant development, we discovered a link between PLS, ethylene signaling, auxin homeostasis, and microtubule cytoskeleton dynamics. Mutation of PLS results in an enhanced ethylene-response phenotype, defective auxin transport and homeostasis, and altered microtubule sensitivity to inhibitors. These defects, along with the short-root phenotype, are suppressed by genetic and pharmacological inhibition of ethylene action. PLS expression is repressed by ethylene and induced by auxin. Our results suggest a mechanism whereby PLS negatively regulates ethylene responses to modulate cell division and expansion via downstream effects on microtubule cytoskeleton dynamics and auxin signaling, thereby influencing root growth and lateral root development. This mechanism involves a regulatory loop of auxin-ethylene interactions.