Release and bioactivity of bone morphogenetic protein-2 are affected by scaffold binding techniques in vitro and in vivo.

A low dose of 1µg rhBMP-2 was immobilised by four different functionalising techniques on recently developed poly(l-lactide)-co-(ε-caprolactone) [(poly(LLA-co-CL)] scaffolds. It was either (i) physisorbed on unmodified scaffolds [PHY], (ii) physisorbed onto scaffolds modified with nanodiamond particles [nDP-PHY], (iii) covalently linked onto nDPs that were used to modify the scaffolds [nDP-COV] or (iv) encapsulated in microspheres distributed on the scaffolds [MICS]. Release kinetics of BMP-2 from the different scaffolds was quantified using targeted mass spectrometry for up to 70days. PHY scaffolds had an initial burst of release while MICS showed a gradual and sustained increase in release. In contrast, NDP-PHY and nDP-COV scaffolds showed no significant release, although nDP-PHY scaffolds maintained bioactivity of BMP-2. Human mesenchymal stem cells cultured in vitro showed upregulated BMP-2 and osteocalcin gene expression at both week 1 and week 3 in the MICS and nDP-PHY scaffold groups. These groups also demonstrated the highest BMP-2 extracellular protein levels as assessed by ELISA, and mineralization confirmed by Alizarin red. Cells grown on the PHY scaffolds in vitro expressed collagen type 1 alpha 2 early but the scaffold could not sustain rhBMP-2 release to express mineralization. After 4weeks post-implantation using a rat mandible critical-sized defect model, micro-CT and Masson trichrome results showed accelerated bone regeneration in the PHY, nDP-PHY and MICS groups. The results demonstrate that PHY scaffolds may not be desirable for clinical use, since similar osteogenic potential was not seen under both in vitro and in vivo conditions, in contrast to nDP-PHY and MICS groups, where continuous low doses of BMP-2 induced satisfactory bone regeneration in both conditions. The nDP-PHY scaffolds used here in critical-sized bone defects for the first time appear to have promise compared to growth factors adsorbed onto a polymer alone and the short distance effect prevents adverse systemic side effects.

Divergence in enzyme regulation between Caenorhabditis elegans and human tyrosine hydroxylase, the key enzyme in the synthesis of dopamine.

TH (tyrosine hydroxylase) is the rate-limiting enzyme in the synthesis of catecholamines. The cat-2 gene of the nematode Caenorhabditis elegans is expressed in mechanosensory dopaminergic neurons and has been proposed to encode a putative TH. In the present paper, we report the cloning of C. elegans full-length cat-2 cDNA and a detailed biochemical characterization of the encoded CAT-2 protein. Similar to other THs, C. elegans CAT-2 is composed of an N-terminal regulatory domain followed by a catalytic domain and a C-terminal oligomerization domain and shows high substrate specificity for L-tyrosine. Like hTH (human TH), CAT-2 is tetrameric and is phosphorylated at Ser35 (equivalent to Ser40 in hTH) by PKA (cAMP-dependent protein kinase). However, CAT-2 is devoid of characteristic regulatory mechanisms present in hTH, such as negative co-operativity for the cofactor, substrate inhibition or feedback inhibition exerted by catecholamines, end-products of the pathway. Thus TH activity in C. elegans displays a weaker regulation in comparison with the human orthologue, resembling a constitutively active enzyme. Overall, our data suggest that the intricate regulation characteristic of mammalian TH might have evolved from more simple models to adjust to the increasing complexity of the higher eukaryotes neuroendocrine systems.

The proteasome inhibitors bortezomib and PR-171 have antiproliferative and proapoptotic effects on primary human acute myeloid leukaemia cells.

Proteasome inhibitors represent a new class of antineoplastic drugs that are considered in the treatment of haematological malignancies. We compared the effects of the reversible proteasome inhibitor bortezomib (Velcade) and the epoxomicin derivative PR-171, an irreversible inhibitor, on primary human acute myeloid leukaemia (AML) cells. Both drugs inhibited autocrine- and cytokine-dependent proliferation of primary AML blasts when tested at nanomolar levels (0.1-100 nmol/l). The antiproliferative effect was independent of basal chymotrypsin-like proteasome activity (showing a 20-fold variation between patients), genetic abnormalities, morphological differentiation and CD34 expression when testing a large group of consecutive patients (n = 54). The effect was retained in cocultures with bone marrow stromal cells. In addition, both drugs enhanced apoptosis. The effect of PR-171 could be detected at lower concentrations than for bortezomib, especially when testing the influence on clonogenic AML cell proliferation. Both drugs had divergent effects on AML cells' constitutive cytokine release. Furthermore, both drugs caused a decrease in proliferation and viability when tested in combination with idarubicin or cytarabine. An antiproliferative effect on primary human acute lymphoblastic leukaemia cells was also detected. We conclude that nanomolar levels of the proteasome inhibitors tested had dose-dependent antiproliferative and proapoptotic effects on primary AML cells in vitro.

Proteomic strategies for individualizing therapy of acute myeloid leukemia (AML).

Acute myeloid leukemia (AML) is an aggressive hematological malignancy characterized by accumulating myeloid precursor cells in the bone marrow, with approximately 2-3 months 50% survival if left untreated. With current treatment modalities the five years overall survival hardly exceeds 50%. Cytogenetics and molecular diagnostics guide the clinician to select individualized therapy in certain subsets of AML, achieving long-term survival above 70% of these cases. However, approximately half of the AML patients have no risk stratifying features, and early reports indicate that proteomic approaches may be utilized for disease classification as well as development of novel biomarkers related to prognosis, diagnosis, and choice of therapeutic regimen. Proteomics, here defined as the analysis of all proteins in a cell, in a cell compartment or in a signaling pathway, has probably its greatest potential in investigating pathways that are easily targeted by small molecules or therapeutic antibodies. The major methodological challenges include detection sensitivity in a limited clinical material, a problem that in some cases can be solved through designated multiplexed protein assays based on single cells or cell extracts. In this review we will discuss pharmacoproteomic studies of drugs regulating leukemia specific targets like all-trans retinoic acid, histone deacetylase inhibitors, proteasome inhibitors and tyrosine kinase inhibitors, as well as studies on drug resistance and graft-versus-host studies during stem cell transplantations. These studies indicate new avenues in AML diagnostics, individualized therapy design and therapy response surveillance for the clinician.

Ubiquitinated annexin A2 is enriched in the cytoskeleton fraction.

Annexin A2 is a multifunctional protein and its cellular functions are regulated by post-translational modifications and ligand binding. When purified from porcine intestinal mucosa and transformed mouse Krebs II cells, SDS-PAGE revealed high-molecular-mass forms in addition to the 36 kDa protomer. These forms were identified as poly-/multi-ubiquitin conjugates of annexin A2, and ubiquitination represents a novel post-translational modification of this protein. Subcellular fractionation of mouse Krebs II cells revealed an enrichment of annexin A2-ubiquitin conjugates in the Triton X-100 resistant cytoskeleton fraction, suggesting that ubiquitinated annexin A2 may have a role associated with its function as an actin-binding protein.

The binding of tyrosine hydroxylase to negatively charged lipid bilayers involves the N-terminal region of the enzyme.

Tyrosine hydroxylase (TH) is the rate-limiting enzyme in the synthesis of catecholamines. We have studied the association of recombinant human TH with model membranes by using either liposomes or silica gel beads coated with single phospholipid bilayers (TRANSIL). The use of TRANSIL beads has allowed the determination of apparent dissociation constants (Kd) for the binding of the enzyme to negatively charged bilayers (Kd=230-380 microM, at pH 6.0-7.0). Binding to the bilayers is accompanied by a decrease in enzyme activity. Proteolysed forms of the enzyme show decreased binding affinity and two putative amphipathic N-terminal alpha-helices are proposed to be involved in membrane binding. As seen by circular dichroism, binding to the bilayer does not seem to induce significant changes on the secondary structure content of the enzyme, but alpha-helical structures appear to be stabilized against thermal denaturation in the membrane-bound state. Thus, amphitropism, a mechanism that regulates the function of peripheral proteins by weak binding to membrane lipids, may add to the factors that regulate both the activity and the stability of TH.

Ubiquitination of soluble and membrane-bound tyrosine hydroxylase and degradation of the soluble form.

Tyrosine hydroxylase (TH) demonstrates by two-dimensional electrophoresis a microheterogeneity both as a soluble recombinant human TH (hTH1) and as a membrane-bound bovine TH (bTHmem). Part of the heterogeneity is likely due to deamidation of labile asparagine residues. Wild-type (wt)-hTH1 was found to be a substrate for the ubiquitin (Ub) conjugating enzyme system in a reconstituted in vitro system. When wt-hTH1 was expressed in a coupled transcription-translation TnT(R)-T7 reticulolysate system 35S-labelled polypeptides of the expected molecular mass of native enzyme as well as both higher and lower molecular mass forms were observed. The amount of high-molecular-mass forms increased by time and was enhanced in the presence of Ub and clasto-lactacystin beta-lactone. In pulse-chase experiments the amount of full-length hTH1 decreased by first-order kinetics with a half-time of 7.4 h and 2.1 h in the absence and presence of an ATP-regenerating system, respectively. The ATP-dependent degradation was inhibited by clasto-lactacystin beta-lactone. Our findings support the conclusion that hTH1 is ubiquitinated and at least partially degraded by the proteasomes in the reticulocyte lysate system. Finally, it is shown that the integral TH of the bovine adrenal chromaffin granule membrane (bTHmem) is ubiquitinated, most likely monoubiquitinated. Additional Ub-conjugates of this membrane, detected by Western blot analysis, have not yet been identified.