Capillary Transfer of Self-Assembled Colloidal Crystals

Colloidal self-assembly has attracted significant interest in numerous applications including optics, electrochemistry, thermofluidics, and biomolecule templating. To meet the requirements of these applications, numerous fabrication methods have been developed. However, these are limited to narrow ranges of feature sizes, are incompatible with many substrates, and/or have low scalability, significantly limiting the use of colloidal self-assembly. In this work, we study the capillary transfer of colloidal crystals and demonstrate that this approach overcomes these limitations. Enabled by capillary transfer, we fabricate 2D colloidal crystals with nano-to-micro feature sizes spanning 2 orders of magnitude and on typically challenging substrates including those that are hydrophobic, rough, curved, or structured with microchannels. We developed and systemically validated a capillary peeling model, elucidating the underlying transfer physics. Due to its high versatility, good quality, and simplicity, this approach can expand the possibilities of colloidal self-assembly and enhance the performance of applications using colloidal crystals.

Temperature-responsive biometamaterials for gastrointestinal applications

We hypothesized that ingested warm fluids could act as triggers for biomedical devices. We investigated heat dissipation throughout the upper gastrointestinal (GI) tract by administering warm (55°C) water to pigs and identified two zones in which thermal actuation could be applied: esophageal (actuation through warm water ingestion) and extra-esophageal (protected from ingestion of warm liquids and actuatable by endoscopically administered warm fluids). Inspired by a blooming flower, we developed a capsule-sized esophageal system that deploys using elastomeric elements and then recovers its original shape in response to thermal triggering of shape-memory nitinol springs by ingestion of warm water. Degradable millineedles incorporated into the system could deliver model molecules to the esophagus. For the extra-esophageal compartment, we developed a highly flexible macrostructure (mechanical metamaterial) that deforms into a cylindrical shape to safely pass through the esophagus and deploys into a fenestrated spherical shape in the stomach, capable of residing safely in the gastric cavity for weeks. The macrostructure uses thermoresponsive elements that dissociate when triggered with the endoscopic application of warm (55°C) water, allowing safe passage of the components through the GI tract. Our gastric-resident platform acts as a gram-level long-lasting drug delivery dosage form, releasing small-molecule drugs for 2 weeks. We anticipate that temperature-triggered systems could usher the development of the next generation of stents, drug delivery, and sensing systems housed in the GI tract.

Light-degradable hydrogels as dynamic triggers for gastrointestinal applications

Triggerable materials capable of being degraded by selective stimuli stand to transform our capacity to precisely control biomedical device activity and performance while reducing the need for invasive interventions. Here, we describe the development of a modular and tunable light-triggerable hydrogel system capable of interfacing with implantable devices. We apply these materials to two applications in the gastrointestinal (GI) tract: a bariatric balloon and an esophageal stent. We demonstrate biocompatibility and on-demand triggering of the material in vitro, ex vivo, and in vivo. Moreover, we characterize performance of the system in a porcine large animal model with an accompanying ingestible LED. Light-triggerable hydrogels have the potential to be applied broadly throughout the GI tract and other anatomic areas. By demonstrating the first use of light-degradable hydrogels in vivo, we provide biomedical engineers and clinicians with a previously unavailable, safe, dynamically deliverable, and precise tool to design dynamically actuated implantable devices.

Loss of p75 neurotrophin receptor expression accompanies malignant progression to human and murine retinoblastoma

We studied the expression of pro-apoptotic neurotrophin receptor p75 (p75(NTR)) in human and murine retinoblastoma, compared to normal retina, and examined changes in p75(NTR) expression with the onset of apoptosis in the course of murine retinoblastoma progression, using immunohistochemistry and quantitative real-time RT-PCR. The murine retinoblastoma is induced by retinal specific expression of SV40 T-antigen (TAg), which blocks the function of the retinoblastoma protein (pRB) and related proteins, and is a well-studied model that closely simulates human retinoblastoma. The majority of human retinoblastoma either lacked or expressed decreased levels of p75(NTR) mRNA, compared to human retina. Moreover, p75(NTR) protein was not detected in any tumor studied, unlike normal retina. Like human retinoblastoma, advanced murine retinoblastoma did not express p75(NTR). However, before tumors emerged, small clusters of TAg-positive cells coexpressed p75(NTR) and activated caspase-3, a marker of apoptosis. Furthermore, in three rare human eyes containing retinoblastoma adjacent to regions resembling the benign retinal tumor retinoma, both normal retina and retinoma-like tissue expressed p75(NTR) protein, while the retinoblastoma did not. We suggest that p75(NTR) loss accompanies progression from retinoma to retinoblastoma.

Identification of a viral kinase that phosphorylates specific E2Fs and pocket proteins

The transcription factor E2F and its regulation by pRB and related pocket proteins are central to cell cycle control in higher eukaryotes. Much of our knowledge of this regulation has come from studies using immediate-early proteins of DNA tumor viruses. Previously, we reported that the 72-kDa immediate-early region 1 gene product of the human cytomegalovirus, IE72, transactivates the dihydrofolate reductase promoter through the E2F site and that it physically interacts with E2F1 (M. J. Margolis, S. Pajovic, E. L. Wong, M. Wade, R. Jupp, J. A. Nelson, and J. C. Azizkhan, J. Virol. 69:7759-7767, 1995). In this study, we further characterized the mechanism by which IE72 modulates E2F-dependent transcription. In vitro phosphorylation reactions using gel-purified bacterially expressed proteins revealed that IE72 is a kinase that autophosphorylates and phosphorylates E2F1, -2, and -3 (but not E2F4 or -5) and the RB-related pocket proteins p130 and p107 (but not pRB). The region of IE72 spanning amino acids 173 to 197 shows a high level of homology to the ATP binding sites in over 500 kinases. The kinase-negative protein IE72deltaATP, from which this region has been deleted, cannot activate E2F-dependent transcription. The kinase activity of IE72 is also required for its ability to reduce the association of E2F4 with p107 and p130. Taken together, these data suggest that the kinase activity of IE72 is required for E2F-dependent transcriptional activation and that this is likely to result from phosphorylation of specific members of the E2F and pocket protein families by IE72.

p53 and WAF1 are induced and Rb protein is hypophosphorylated during cell growth inhibition by the thymidylate synthase inhibitor ZD1694 (Tomudex)

In a previous study, we found that treatment of HCT-8 cells with ZD1694, a specific antifolate-based thymidylate synthase inhibitor, resulted in DNA fragmentation. In this study, we have demonstrated the dose- and time-dependent induction of DNA fragmentation accompanied by elevation of p53 and WAF1 protein expression by ZD1694. WAF1 mRNA showed a time-dependent increase, whereas p53 mRNA was not found to be significantly overexpressed. The initial increase in WAF1 mRNA was detected at 4 hr, but increased WAF1 protein expression was detected 8-24 hr after a 2-hr exposure. The amount of total and hypophosphorylated pRb seems to be rising greatly after ZD1694 exposure. The effects of ZD1694 on the expression of E2F1 and formation of the E2F1-Rb complex were investigated after a 2-hr drug exposure (IC90). The results showed a time-dependent decrease in E2F1 mRNA and protein expression; an increase in the abundance of the E2F-Rb complex could be demonstrated beginning 4 hr after drug exposure by a gel shift assay. Kinetic analysis showed increased availability of hypophosphorylated pRb for inhibition of E2F, which could indirectly result from WAF1-induced inhibition cyclin-dependent kinase activity. Whereas thymidylate synthase inhibition by ZD1694 was rapid in onset and maintained for at least 24 hr after drug treatment, drug-induced cellular growth inhibition was significant 24 hr after drug exposure. The increased abundance of hypophosphorylated pRb and binding to transcription factor E2F-1 is consistent with ZD1694-induced cell growth inhibition in HCT-8 cells. Therefore, the observed effect on downstream events after effective inhibition of thymidylate synthase may offer the critical determinants of response to ZD1694.

Cell cycle-regulated association of E2F1 and Sp1 is related to their functional interaction

Because of the large number of growth-regulated genes containing binding sites for the transcription factors Sp1 and E2F and the reported ability of E2F to mediate cell cycle (growth) regulation, we studied interactions between E2F1 and Sp1. In transient transfection assays using Drosophila melanogaster SL2 cells, transfection with both Sp1 and E2F1 expression vectors resulted in greater than 85-fold activation of transcription from a hamster dihydrofolate reductase reporter construct, whereas cotransfection with either the Sp1 or E2F1 expression vector resulted in 30- or <2-fold activation, respectively. Therefore, these transcription factors act synergistically in activation of dihydrofolate reductase transcription. Transient transfection studies demonstrated that E2F1 could superactivate Sp1-dependent transcription in a promoter containing only Sp1 sites and that Sp1 could superactivate transcription of promoters through E2F sites, further demonstrating that these physically associated in Drosophila cells transfected with Sp1 and E2F1 expression vectors and in human cells, with maximal interaction detected in mid- to late G1. Additionally, E2F1 and Sp1 interact in vitro through specific domains of each protein, and the physical interaction and functional synergism appear to require the same regions. Taken together, these data demonstrate that E2F1 and Sp1 both functionally and physically interact; therefore this interaction, Sp1 and E2F1 may regulate transcription of genes containing binding sites for either or both factors.

Interaction of the 72-kilodalton human cytomegalovirus IE1 gene product with E2F1 coincides with E2F-dependent activation of dihydrofolate reductase transcription

Three polypeptides are produced from the major immediate-early (IE) region of human cytomegalovirus by alternative splicing. The IE gene products regulate subsequent viral and cellular gene expression. We previously reported that cotransfection of a genomic clone of the major IE region stimulated transient expression of chloramphenicol acetyltransferase driven by the dihydrofolate reductase (DHFR) promoter and that an intact E2F site was required for the trans activation (M. Wade, T. F. Kowalik, M. Mudryj, E.-S. Huang, and J. C. Azizkhan, Mol. Cell. Biol. 12:4364-4374, 1992). With the availability of cDNA clones for the individual major IE proteins, we sought to determine which of these proteins exerted this effect and whether the IE protein(s) interacted with E2F. In this study, we use cotransfection to demonstrate that the 55- and 86-kDa major IE proteins from the IE2 region can each moderately trans activate the DHFR promoter and that the 72-kDa IE1 protein stimulates DHFR transcription to a much higher level. Furthermore, trans activation through the 72-kDa IE1 protein is in part E2F dependent, while activation by the 55- and 86-kDa IE proteins is E2F independent. We also demonstrate by in vitro pull-down assays that the 72-kDa IE1 protein can specifically interact with the DNA binding domain of E2F1 (amino acids 88 to 191) in the presence of nuclear extract. Moreover, antibodies to either E2F1 or IE72 will immunoprecipitate both E2F and IE72 from cells that stably express IE72, and antibody to E2F1 will immunoprecipitate IE72 from normal human fibroblast cells infected with human cytomegalovirus.

Species-specific changes in regulatory elements of mouse haptoglobin genes

Although expression of the haptoglobin (HP) as an acute phase reactant is evolutionarily conserved among mammals, there are differences among species with regard to the hormones required for stimulation. Using primary hepatocyte cultures, we show that in Mus caroli, as in rat, IL-1 and IL-6 are stimulatory, whereas in M. domesticus, as in humans, IL-1 response is diminished. In vivo, an acute inflammatory process increases hepatic HP expression in both mouse species up to 30-fold but minimally affects the low level HP expression in the lung. To define the species-specific differences in regulation, we isolated the hormone-responsive elements of the HP gene from the Mus species, M. domesticus, M. caroli, and M. saxicola. Functional studies in transfected hepatoma cells revealed an exceptionally strong dexamethasone response for all three murine HP gene elements. The IL-6 response was less prominent than in rat or human. A modest response to IL-1 was observed in M. caroli and M. saxicola. A mouse-specific insertion of a polypurine sequence led to a binding site for the PEA3 transcription factor in the HP gene promoter of M. domesticus and M. saxicola, but not M. caroli. The specific regulatory effects of glucocorticoid receptor, C/EBP beta, and Ets proteins were documented by co-transfection.

Reconstitution of the response to leukemia inhibitory factor, oncostatin M, and ciliary neurotrophic factor in hepatoma cells

Ciliary neurotrophic factor (CNTF) has been described as a neuro-active cytokine that shares functional similarities with the leukemia inhibitory factor (LIF). We demonstrate here that, like LIF, CNTF stimulates expression of acute phase plasma proteins in rat H-35 hepatoma cells. Transfection of the LIF receptor into Hep3B hepatoma cells reconstituted LIF and oncostatin M regulation of acute phase plasma protein genes. Co-expression of the LIF receptor and the CNTF receptor, but not expression of either subunit alone, generated CNTF responsiveness in Hep3B cells, suggesting cooperativity of these receptor subunits. Evidence is presented for direct interaction of the LIF receptor with the intracellular signal transduction machinery.