Virosome-mediated implantation of red cell band 3 into the plasma membrane of cultured hepatoma cells

A composite gene delivery system consisting of polyethylenimine and an amphipathic peptide KALA

BACKGROUND

Animal viruses such as enveloped virus carry multi-functional proteins in the virion that can mediate more than two distinct steps of a gene delivery process during the transfer of viral genome into host cells. We tested if the aspects of the viral gene delivery mechanism could be mimicked by forming composite formulae from multi-functional synthetic gene carriers having complementary action modes.

METHODS

Polyethylenimine (PEI) was chosen as the component responsible for endosome escape and DNA condensation and KALA for cellular entry and DNA condensation. Compact DNA-carrier particles consisting of the core part where DNA chains were tightly condensed by PEI and the outer layer lined with KALA were formulated, characterized and compared with monolithic cationic formulae in terms of gene delivery efficiency and mechanism.

RESULTS

High-level gene expression was observed when C2C12 cells were transfected with DNA that was first partially condensed with PEI and, then, fully with KALA. In these formulae KALA mediated enhanced cellular entry of DNA by facilitating endocytic vesicle formation, while PEI provided an effective endosomolytic capacity. An optimal PEI/KALA formula showed transfection efficiencies better than or comparable to the commercial cationic liposome in various cell types in culture and in vivo.

CONCLUSIONS

Gene delivery by combining the membrane-active property of KALA with the endosomolytic activity of PEI can be more efficient than that by either of the properties alone. It appears that, in these formulae, the predominant role of KALA is to facilitate cellular entry of DNA by providing a fusogenic capability, rather than an endosomolytic activity.

Incorporation of proteins into (Xenopus) oocytes by proteoliposome microinjection: functional characterization of a novel aquaporin

Xenopus laevis oocytes are widely used as an expression system for plasma membrane proteins, achieved by cytoplasmic microinjection of messenger RNA. In the present study, we propose an alternative system allowing functional insertion of exogenous proteins into the plasma membrane of Xenopus oocytes. We microinjected proteoliposome suspensions into the cytoplasm and then analyzed membrane protein function. The proteins used in this work were members of the MIP family: the human erythrocyte water channel aquaporin 1 (AQP1), the major intrinsic protein (MIP26) from bovine eye lens and a 25 kDa polypeptide (P25) from a water shunting complex found in the digestive tract of an homopteran sap-sucking insect (Cicadella viridis). Proteoliposomes containing either AQP1, MIP26, or P25 were injected into Xenopus oocytes. The subsequent insertion of these proteins into the plasma membrane of oocytes was demonstrated by immunocytochemistry. Oocytes microinjected with either AQP1 or P25-proteoliposomes exhibited significantly increased osmotic membrane water permeabilities (Pf = 3.16 +/- 026 and 4.03 +/- 0.26 × 10(−3) cm/second, respectively) compared to those measured for oocytes injected with liposomes alone or with MIP26-proteoliposomes (Pf = 1.39 +/- 0.07 and 1.44 +/- 0.10 × 10(−3) cm/second, respectively). These effects were inhibited by HgCl2 in a reversible manner. Arrhenius activation energies of water transfer were low when AQP1 or P25 were present in oocyte plasma membranes (Ea = 2.29 and 3.01 kcal/mol, respectively, versus Ea = 11.75 kcal/mol for liposome injected oocytes). The properties observed here for AQP1 are identical to those widely reported following AQP1 cRNA expression in oocytes. From the present study, we conclude that: (1) exogenous plasma membrane proteins incorporated into liposomes and microinjected into the cytoplasm of Xenopus oocytes are subsequently found in the plasma membrane of the oocytes in a functional state; and (2) in this system, the P25 polypeptide from the MIP family found in the digestive tract of Cicadella viridis exhibits properties similar to those described for the archetype of water channels AQP1, and thus is a new member of the aquaporin family.

Sendai-viral HN and F glycoproteins as probes of plasma-membrane protein catabolism in HTC cells. Studies with fusogenic reconstituted Sendai-viral envelopes

Reconstituted Sendai-viral envelopes (RSVE) were produced by the method of Vainstein, Hershkovitz, Israel & Loyter [(1984) Biochim. Biophys. Acta 773, 181-188]. RSVE are fusogenic unilamellar vesicles containing two transmembrane glycoproteins: the HN (haemagglutinin-neuraminidase) protein and the F (fusion) factor. The fate of the viral proteins after fusion-mediated transplantation of RSVE into hepatoma (HTC) cell plasma membranes was studied to probe plasma-membrane protein degradation. Both protein species are degraded at similar, relatively slow, rates (t1/2 = 67 h) in HTC cells fused with RSVE in suspension. Even slower degradation rates for HN and F proteins (t1/2 = 93 h) were measured when RSVE were fused with HTC cells in monolayer. Lysosomal degradation of the transplanted viral proteins is strongly implicated by the finding that degradation of HN and F proteins is sensitive to inhibition by 10 mM-NH4Cl (81%) and by 50 micrograms of leupeptin/ml (70%).

Degradation of exogenous membrane proteins implanted into the plasma membrane of cultured hepatoma cells

The degradation of radiolabeled red cell band 3 and Sendai envelope proteins was studied after band 3 virosomes were fused with hepatoma cells as previously described (Hare, J E & Huston, M, Exp cell res 161 (1986) 317) [26]. 125I-band 3 (T1/2 = 13-14 h), Sendai HN (T1/2 = 37-40 h), and F (T1/2 = 21-23 h) envelope proteins were degraded by an apparent first-order process that was greater than 90% sensitive to 20 mM NH4Cl. 125I-Sendai envelope proteins were degraded at approximately similar rates when hepatoma cells were fused with intact virus, isolated viral membrane, or band 3 virosomes. There thus appears to be distinct heterogeneity among the degradation rates of implanted polypeptides dependent on structural aspects of each. To identify the subcellular site of membrane protein degradation, band 3 was labeled with membrane impermeant [14C]sucrose and implanted into hepatoma plasma membranes. After replating, trichloroacetic acid (TCA)-soluble label was found to accumulate in the lysosomal compartment of fractionated cells. The results identify the lysosome as the ultimate site of plasma membrane protein degradation, but suggest that plasma membrane proteins are selectively rather than non-selectively delivered to this compartment.