Development of tissue-engineered models of oral dysplasia and early invasive oral squamous cell carcinoma.

BACKGROUND: Current organotypic models of dysplasia and oral squamous cell carcinoma (OSCC) lack the complexity that mimics in vivo tissue. Here we describe a three-dimensional in vitro model of the oral epithelium that replicates tumour progression from dysplasia to an invasive phenotype. METHODS: The OSCC cell lines were seeded as a cell suspension (D20, Cal27) or as multicellular tumour spheroids (FaDu) with oral fibroblasts on to a de-epidermised acellular dermis to generate tissue-engineered models and compared with patient biopsies. RESULTS: The D20 and Cal27 cells generated a model of epithelial dysplasia. Overtime Cal27 cells traversed the basement membrane and invaded the connective tissue to reproduce features of early invasive OSCC. When seeded onto a model of the normal oral mucosa, FaDu spheroids produced a histological picture mimicking carcinoma in situ with severe cellular atypia juxtaposed to normal epithelium. CONCLUSION: It is possible to culture in vitro models with the morphological appearance and histological characteristics of dysplasia and tumour cell invasion seen in vivo using native dermis. Such models could facilitate study of the molecular processes involved in malignant transformation, invasion and tumour growth as well as in vitro testing of new treatments, diagnostic tests and drug delivery systems for OSCC.

Post-translational modification of polyketide and nonribosomal peptide synthases.

The past year has witnessed a major advance in the study of polyketide and nonribosomal peptide biosynthesis with the identification of the phosphopantetheinyl transferase enzyme family, enzymes required to produce active, post-translationally modified polyketide and peptide synthases. Phosphopantetheinyl transferases required for fatty acid, peptide and siderophore biosynthesis have been characterized and a consensus sequence noted in order to facilitate future identification of additional proteins catalyzing phosphopantetheinyl transfer.

The core Alzheimer's peptide NAC forms amyloid fibrils which seed and are seeded by beta-amyloid: is NAC a common trigger or target in neurodegenerative disease?

BACKGROUND: NAC is a 35-amino-acid peptide which has been isolated from the insoluble core of Alzheimer's disease (AD) amyloid plaque. It is a fragment of alpha-synuclein (or NACP), a neuronal protein of unknown function. We noted a striking sequence similarity between NAC, the carboxyl terminus of the beta-amyloid protein, and a region of the scrapie prion protein (PrP) which has been implicated in amyloid formation. RESULTS: NAC was prepared by chemical synthesis and was found to form amyloid fibrils via a nucleation-dependent polymerization mechanism. NAC amyloid fibrils effectively seed beta 1-40 amyloid formation. Amyloid fibrils comprising peptide models of the homologous beta and PrP sequences were also found to seed amyloid formation by NAC. CONCLUSIONS: The in vitro model studies presented here suggest that seeding of NAC amyloid formation by the beta-amyloid protein, or seeding of amyloid fibrils of the beta-amyloid protein by NAC, may occur in vivo. Accumulation of ordered NAC aggregates in the synapse may be responsible for the neurodegeneration observed in AD and the prion disorders. Alternatively, neurodegeneration may be caused by the loss of alpha-synuclein (NACP) function.

Identification of a Mycobacterium tuberculosis gene cluster encoding the biosynthetic enzymes for assembly of the virulence-conferring siderophore mycobactin.

BACKGROUND: Many pathogenic bacteria secrete iron-chelating siderophores as virulence factors in the iron-limiting environments of their vertebrate hosts to compete for ferric iron. Mycobacterium tuberculosis mycobactins are mixed polyketide/nonribosomal peptides that contain a hydroxyaryloxazoline cap and two N-hydroxyamides that together create a high-affinity site for ferric ion. The mycobactin structure is analogous to that of the yersiniabactin and vibriobactin siderophores from the bacteria that cause plague and cholera, respectively. RESULTS: A ten-gene cluster spanning 24 kilobases of the M. tuberculosis genome, designated mbtA-J, contains the core components necessary for mycobactin biogenesis. The gene products MbtB, MbtE and MbtF are proposed to be peptide synthetases, MbtC and MbtD polyketide synthases, MbtI an isochorismate synthase that provides a salicylate activated by MbtA, and MbtG a required hydroxylase. An aryl carrier protein (ArCP) domain is encoded in mbtB, and is probably the site of siderophore chain initiation. Overproduction and purification of the mbtB ArCP domain and MbtA in Escherichia coli allowed validation of the mycobactin initiation hypothesis, as sequential action of PptT (a phosphopantetheinyl transferase) and MbtA (a salicyl-AMP ligase) resulted in the mbtB ArCP domain being activated as salicyl-S-ArCP. CONCLUSIONS: Mycobactins are produced in M. tuberculosis using a polyketide synthase/nonribosomal peptide synthetase strategy. The mycobactin gene cluster has organizational homologies to the yersiniabactin and enterobactin synthetase genes. Enzymatic targets for inhibitor design and therapeutic intervention are suggested by the similar ferric-ion ligation strategies used in the siderophores from Mycobacteria, Yersinia and E. coli pathogens.

Overexpression of the alpha v beta 6 integrin in cervical squamous cell carcinoma is a prognostic factor for decreased survival.

Cervical squamous cell carcinomas are composed histologically of tumour cell islands surrounded by varying amounts of tumour stroma, the amount and composition of which are influenced by local TGF-beta(1). TGF-beta(1) is secreted in an inactive complex with latency-associated peptide (LAP). Both LAP and the extracellular matrix (ECM) protein fibronectin are important ligands for the integrin receptor alpha v beta 6. While alpha v beta 6 is only weakly expressed by normal epithelia, it is up-regulated in different carcinomas where it generally reflects a more aggressive phenotype. In cervical cancer, the expression of alpha v beta 6 has not thus far been investigated. Given the ability of alpha v beta 6 both to activate TGF-beta(1) and to interact with fibronectin, we studied correlations between the expression of these components and disease parameters in a large cohort of cervical cancer specimens. We analysed alpha v beta 6 expression using immunohistochemistry in primary cervical squamous carcinomas of FIGO stage IA to IIB patients and correlated the findings with formerly investigated fibronectin and TGF-beta(1) expression and clinico-pathological parameters. alpha v beta 6 expression was also examined in cervical intra-epithelial neoplasia (CIN) and lymph node metastases. alpha v beta 6 was only weakly expressed in normal epithelium but clearly up-regulated in CIN lesions. In carcinomas, strong expression of alpha v beta 6 in tumour cells correlated with different clinico-pathological parameters and with worse overall and disease-free survival. Furthermore, alpha v beta 6 expression correlated positively with TGF-beta(1) mRNA expression as well as with fibronectin expression. Overexpression of alpha v beta 6 in cervical squamous carcinomas is an unfavourable prognostic factor. This might reflect an increased capacity of alpha v beta 6-expressing tumour cells to migrate in a fibronectin-rich ECM and/or to activate TGF-beta(1) at the tumour/stroma interface, both of which processes may contribute to cervical cancer progression.

NACP, a protein implicated in Alzheimer's disease and learning, is natively unfolded.

The "non-A beta component of Alzheimer's disease amyloid plaque" (NAC) is a minor peptide component of the insoluble fibrillar core of the Alzheimer's disease (AD) neuritic plaque. NAC amyloid fibrils seed the polymerization of A beta 1-40, the major AD amyloid protein. NAC is derived from a 14 kDa precursor protein, designated NACP, a member of a highly conserved family of heat-stable brain-specific acidic proteins which have been suggested to be involved in synapse formation and/or stabilization. NACP has also been suggested to play a role in AD. We present herein a conformational analysis of human NACP. NACP has a much larger Stokes radius (34 A) but sedimented more slowly (s20,w = 1.7S) than globular proteins of similar molecular weight, indicating that the native protein is elongated. Circular dichroism (CD) and Fourier-transform infrared spectroscopy (FTIR) indicate the absence of significant amounts of secondary structure in NACP, while CD and ultraviolet spectroscopy suggest the lack of a hydrophobic core. The conformational properties of NACP were unchanged by boiling and were independent of concentration, pH, salt, and chemical denaturants. These features indicate that NACP exists as a mixture of rapidly equilibrating extended conformers and is representative of a class of "natively unfolded" proteins, many of which potentiate protein-protein interactions.

Stoichiometry and specificity of in vitro phosphopantetheinylation and aminoacylation of the valine-activating module of surfactin synthetase.

Surfactin synthetase is the enzyme responsible for biosynthesis of the lipoheptapeptide antibiotic surfactin by Bacillus subtilis. Fragments of SrfB1, the L-valine-activating module of the second subunit of surfactin synthetase, were overproduced in Escherichia coli. In addition to a 143-kDa SrfB1 fragment that contains four domains putatively involved in activation (adenylation domain), autoaminoacylation (peptidyl carrier protein (PCP) domain), and peptide bond formation (two condensation domains), subfragments comprising two domains (104-kDa condensation-adenylation and 73-kDa adenylation-PCP), and one domain (18-kDa PCP) were also overproduced in and purified from E. coli as N-terminal hexahistidine fusion proteins. Incubation of these domains with pure Sfp, a phosphopantetheinyl transferase (PPTase) from B. subtilis, and CoA allowed quantitation of posttranslational phosphopantetheinylation of Ser999 by mass spectrometry for the 18-kDa PCP fragment and by radioassay using cosubstrate [3H] pantetheinyl-coenzyme A for all PCP-containing constructs. The phosphopantetheine stoichiometry correlated with the subsequent mole fractions of [14C] valyl groups that could be covalently transferred to these holo-PCP domains. In turn, the catalytic efficiency of intramolecular aminoacylation of the 143-kDa fragment could be compared with the reaction "in trans" between adenylation and PCP fragments of SrfB1. The corresponding holo-PCP domain of the next module, SrfB2, was not detectably aminoacylated by SrfB1, indicative of protein-protein recognition between adenylation and cognate PCP domains. These results should permit future exploration of the timing and specificity of peptide bond formation by this class of biosynthetic enzymes.

Characterization of Sfp, a Bacillus subtilis phosphopantetheinyl transferase for peptidyl carrier protein domains in peptide synthetases.

The Bacillus subtilis enzyme Sfp, required for production of the lipoheptapeptide antibiotic surfactin, posttranslationally phosphopantetheinylates a serine residue in each of the seven peptidyl carrier protein domains of the first three subunits (SrfABC) of surfactin synthetase to yield docking sites for amino acid loading and peptide bond formation. With recombinant Sfp and 16-17-kDa peptidyl carrier protein (PCP) domains excised from the SrfB1 and SrfB2 modules as apo substrates, kcat values of 56-104 min-1 and K(m) values of 1.3-1.8 microM were determined, indicating equivalent recognition of the adjacent PCP domains by Sfp. In contrast to other phosphopantetheinyl transferases (PPTases) previously examined, Sfp will modify the apo forms of heterologous recombinant proteins, including the PCP domain of Saccharomyces cerevisiae Lys2 (involved in lysine biosynthesis), the aryl carrier protein (ArCP) domain of Escherichia coli EntB (involved in enterobactin biosynthesis), and the E. coli acyl carrier protein (ACP) subunit, suggesting Sfp as a good candidate for heterologous coexpression with peptide and polyketide synthase genes to overproduce holo-synthase enzymes. Cosubstrate coenzyme A (CoA), the phosphopantetheinyl group donor, has a K(m) of 0.7 microM. Desulfo-CoA and homocysteamine-CoA are also substrates of Sfp, and benzoyl-CoA and phenylacetyl-CoA are also utilized by Sfp, resulting in direct transfer of acyl phosphopantetheinyl moieties into the carrier protein substrate. Mutagenesis in Sfp of five residues conserved across the PPTase family was assessed for in vivo effects on surfactin production and in vitro effects on PPTase activity.

Isolation and characterization of EMS16, a C-lectin type protein from Echis multisquamatus venom, a potent and selective inhibitor of the alpha2beta1 integrin.

We have isolated and characterized EMS16, a potent and selective inhibitor of the alpha2beta1 integrin, from Echis multisquamatus venom. It belongs to the family of C-lectin type of proteins (CLPs), and its amino acid sequence is homologous with other members of this protein family occurring in snake venoms. EMS16 (M(r) approximately 33K) is a heterodimer composed of two distinct subunits linked by S-S bonds. K562 cells transfected with alpha2 integrin selectively adhere to immobilized EMS16, but not to two other snake venom-derived CLPs, echicetin and alboaggregin B. EMS16 inhibits adhesion of alpha2beta1-expressing cells to immobilized collagen I at picomolar concentrations, and the platelet/collagen I interaction in solution at nanomolar concentrations. EMS16 inhibits binding of isolated, recombinant I domain of alpha2 integrin to collagen in an ELISA assay, but not the interaction of isolated I domain of alpha1 integrin with collagen IV. Studies with monoclonal antibodies suggested that EMS16 binds to the alpha2 subunit of the integrin. EMS16 inhibits collagen-induced platelet aggregation, but has no effect on aggregation induced by other agonists such as ADP, thromboxane analogue (U46619), TRAP, or convulxin. EMS16 also inhibits collagen-induced, but not convulxin-induced, platelet cytosolic Ca(2+) mobilization. In addition, EMS16 inhibits HUVEC migration in collagen I gel. In conclusion, we report a new, potent viper venom-derived inhibitor of alpha2beta1 integrin, which does not belong to the disintegrin family.

Enhanced potency of human Sonic hedgehog by hydrophobic modification.

Post-translational modifications of the developmental signaling protein Sonic hedgehog (Shh) by a long-chain fatty acid at the N-terminus and cholesterol at the C-terminus greatly activate the protein in a cell-based signaling assay. To investigate the structural determinants of this activation phenomenon, hydrophobic and hydrophilic moieties have been introduced by chemical and mutagenic methods to the soluble N-terminal signaling domain of Shh and tested in both in vitro and in vivo assays. A wide variety of hydrophobic modifications increased the potency of Shh when added at the N-terminus of the protein, ranging from long-chain fatty acids to hydrophobic amino acids, with EC(50) values from 99 nM for the unmodified protein to 0.6 nM for the myristoylated form. The N-myristoylated Shh was as active as the natural form having both N- and C-terminal modifications. The degree of activation appears to correlate with the hydrophobicity of the modification rather than any specific chemical feature of the adduct; moreover, substitution with hydrophilic moieties decreased activity. Hydrophobic modifications at the C-terminus of Shh resulted in only a 2-3-fold increase in activity, and no activation was found with hydrophobic modification at other surface positions. The N-terminal modifications did not appear to alter the binding affinity of the Shh protein for the transfected receptor protein, Patched, and had no apparent effect on structure as measured by circular dichroism, thermal denaturation, and size determination. Activation of Desert Hh through modification of its N-terminus was also observed, suggesting that this is a common feature of Hh proteins.