Cell substrate adhesion-induced redistribution of proteins among the apical, basal, and internal domains of the plasma membrane of HeLa cells spreading on gelatin

Mass production of early-stage bone-marrow-derived mesenchymal stem cells of rat using gelatin-coated matrix

Although preparation of early-stage bone-marrow-derived mesenchymal stem cells (BM-MSCs) is critical for successful cell transplantation therapy, no culture system offers a sufficient number of early-stage BM-MSCs for cell transplantation. Accordingly, we developed a culture system capable of producing a large number of early-stage BM-MSCs by using gelatin-coated matrix. The greatest retrieval and proliferation rates of the earliest-stage rat BM-MSCs were detected in bone-marrow-derived cells cultured on 1% (wt/v) gelatin-coated matrix, which showed significantly greater colony forming unit-fibroblast number, diameter, and total cell number. Moreover, continuous culture of the earliest-stage BM-MSCs on 1% (wt/v) gelatin-coated matrix resulted in a maximum of 21.2 ± 2.7 fold increase in the cumulative total number of early-stage BM-MSCs at passage 5. BM-MSCs generated in large quantities due to a reduced doubling time and an increased yield of cell population in S/G2/M phase showed typical fibroblast-like morphology and no significant differences in BM-MSC-related surface marker expression and differentiation potential, except for an increased ratio of differentiation into a neurogenic lineage. The use of gelatin-coated matrix in the retrieval and culture of BM-MSCs contributes greatly to the effective isolation and mass production of early-stage BM-MSCs.

Cell cycle dependent changes in membrane stored curvature elastic energy: evidence from lipidomic studies

One of the most developed theories of phospholipid homeostasis is the intrinsic curvature hypothesis, which, in broad terms, postulates that cells regulate their lipid composition so as to keep constant the membrane stored curvature elastic energy. The implication of this hypothesis is that lipid composition is determined by a ratio control function consisting of the weighted sum of concentrations of type II lipids in the numerator and the weighted sum of concentrations of Type 0 lipids in the denominator. In previous work we used a data-driven approach, based on lipidomic data from asynchronous cell cultures, to determine a criterion that allows the different lipid species to be assigned to the set of type 0 or of type II lipids, and hence construct a ratio control function that serves as a proxy for the lipid contribution to total membrane stored curvature elastic energy in vivo. Here we apply the curvature elastic energy proxy to the analysis of lipid composition data from synchronous HeLa cells as they traverse the cell cycle. Our analysis suggests HeLa cells modify their membrane stored elastic energy through the cell cycle. In S-phase type 0 lipids are the most abundant, whilst in G2 type II lipids are most abundant. Changes in our proxy for membrane stored elastic energy correlate with membrane curvature dependent processes in the HeLa cell around division, providing some insights into the interplay between the individual lipid and protein contributions to membrane free energy.

Derlin-1 is overexpressed on the tumor cell surface and enables antibody-mediated tumor targeting therapy

PURPOSE

Tumor targeting therapy is one of the most promising strategies for anticancer treatment. Derlin-1 has been reported to participate in misfolded protein dislocation and integrates into the endoplasmic reticulum (ER) membrane to survey for such protein aggregates. We elucidate herein that Derlin-1 can leak to the plasmalemma from the ER in tumor cells and may have clinical application as a novel cancer target in the hope of developing a new tumor targeting therapy.

EXPERIMENTAL DESIGN

The cell surface expression of Derlin-1 was shown by immunofluorescence analysis of nonpermeabilized cells and Western blotting of fractional proteins of tumor cells. Derlin-1 expression in cancerous tissues was also shown by immunohistochemistry. Biodistribution analysis and gamma-scintigraphic imaging were done using (125)I-labeled Derlin-1 targeting antibody in isogenic mice models. Finally, tumor-bearing mice were treated by the anti-Derlin-1 polyclonal antibody and monoclonal antibodies.

RESULTS

Derlin-1 was expressed on various tumor cell surfaces and adopted a homodimer conformation. Robust cytoplasmic and membrane expression of Derlin-1 was detected in various types of human cancers tissues but was not correlated with any clinicopathologic features of pancreatic cancer. Derlin-1 directed antibodies specifically targeted to colon tumors and significantly suppress tumor growth in isogenic mice.

CONCLUSIONS

These preclinical data show that Derlin-1 protein is a functional molecular target expressed on the tumor cell surface and is a candidate therapeutic target that may be translated into clinical applications.

A novel gellan gel-based microcarrier for anchorage-dependent cell delivery

Competent vehicles are highly sought after as a means to transplant cells for tissue regeneration. In this study, novel hydrogel-based microspherical cell carriers are designed and developed with an FDA-approved natural polysaccharide, gellan gum. The bulk fabrication of these microspheres is performed via a water-in-oil (W/O) emulsion process followed by a series of redox (oxidation-reduction) crosslinking treatments; this enables the microspherical dimensions to be precisely manipulated in terms of injectability, and simultaneously ensures the structural stability. To acquire adhesion affinity with anchorage-dependent cells (ADCs), a covalent coating of gelatin is further applied on the microspherical surfaces. The final product is constructed as a variety of gelatin-grafted-gellan microspherical cell carriers, abbreviated as "TriG" microcarriers. The cell-loading tests are conducted, respectively, with human dermal fibroblasts (HDFs) and human fetal osteoblasts (hFOBs). Morphological observation from optical microscopy and field emission scanning electron microscopy indicates that the HDFs spread well and populate rapidly on surfaces of TriG microcarriers. Immunofluorescent staining reveals the activation of focal adhesion and subsequent organization of F-actin from the attached cell surfaces, which suggests the TriG microspherical substrate is favorable to ADC adhesion and therefore capable of promoting HDF proliferation to achieve confluence by turning over three times within 10 days. The hFOBs are also cultivated on the TriG carriers, where ideal viability and clear potentials for osteogenesis are demonstrated by fluorescent "Live/Dead" screening and specific histobiochemical indications. All these findings suggest that the TriG microcarriers are suitable to provide open platforms for therapeutic ADC proliferation and differentiation.

Arachidonate initiated protein kinase C activation regulates HeLa cell spreading on a gelatin substrate by inducing F-actin formation and exocytotic upregulation of beta 1 integrin

HeLa cell spreading on a gelatin substrate requires the activation of protein kinase C (PKC), which occurs as a result of cell-attachment-induced activation of phospholipase A2 (PLA2) to produce arachidonic acid (AA) and metabolism of AA by lipoxyginase (LOX). The present study examines how PKC activation affects the actin- and microtubule-based cytoskeletal machinery to facilitate HeLa cell spreading on gelatin. Cell spreading on gelatin is contingent on PKC induction of both actin polymerization and microtubule-facilitated exocytosis, which is based on the following observations. There is an increase in the relative content of filamentous (F)-actin during HeLa cell spreading, and treating HeLa cells with PKC-activating phorbol esters such as 12-O-tetradecanoyl phorbol 13-acetate (TPA) further increases the relative content of F-actin and the rate and extent to which the cells spread. Conversely, inhibition of PKC by calphostin C blocked both cell spreading and the increase of F-actin content. The increased F-actin content induced by PKC activators also was observed in suspension cells treated with TPA, and the kinetics of F-actin were similar to that for PKC activation. In addition, PKC epsilon, which is the PKC isoform most involved in regulating HeLa cell spreading in response to AA production, is more rapidly translocated to the membrane in response to TPA treatment than is the increase in F-actin. Blocking the activities of either PLA2 or LOX inhibited F-actin formation and cell spreading, both of which were reversed by TPA treatment. This result is consistent with AA and a LOX metabolite of AA as being upstream second messengers of activation of PKC and its regulation of F-actin formation and cell spreading. PKC appears to activate actin polymerization in the entire body of the cell and not just in the region of cell-substrate adhesion because activated PKC was associated not only with the basolateral plasma membrane domain contacting the culture dish but also with the apical plasma membrane domain exposed to the culture medium and with an intracellular membrane fraction. In addition to the facilitation of F-actin formation, activation of PKC induces the exocytotic upregulation of beta 1 integrins from an intracellular domain to the cell surface, possibly in a microtubule-dependent manner because the upregulation is inhibited by Nocodazole. The results support the concept that cell-attachment-induced AA production and its metabolism by LOX results in the activation of PKC, which has a dual role in regulating the cytoskeletal machinery during HeLa cell spreading. One is through the formation of F-actin that induces the structural reorganization of the cells from round to spread, and the other is the exocytotic upregulation of collagen receptors to the cell surface to enhance cell spreading.

Isolation of the plasma membrane and organelles from Chinese hamster ovary cells

Two methods are described enabling the plasma membrane from Chinese hamster ovary (CHO) cells to be obtained rapidly, relatively pure and with a good yield. In both cases, cells were disrupted by nitrogen cavitation in an isoosmotic buffer either at pH 5.4 or at pH 7.4. In the first approach, cells were lysed at pH 7.4 and the plasma membrane and cell organelles were isolated on a self-generated gradient of Percoll, at neutral pH. Mitochondria and endoplasmic reticulum were recovered in the denser fractions, plasma membrane fragments were found in the lighter fractions, but always contaminated by lysosomes. Because lysosomes were found to sediment in acidic conditions, cells were lysed at pH 5.4 and presedimentation (1500 x g) of the cell homogenate at the same pH enabled more than 80% of the lysosomes to be removed. Then, ultracentrifugation of the supernatant over a Percoll gradient at neutral pH yielded plasma membrane fractions practically free of lysosomes with an enrichment ratio of 3 and fractions of mitochondria and endoplasmic reticulum with enrichment ratios of 17 and 6, respectively. A major problem was encountered in the final step of elimination of Percoll from the purified plasma membrane fractions. Whatever the technique used for eliminating Percoll, plasma membranes were observed to be contaminated by a Percoll constituent which prevented further purification and biochemical identification of the lipids extracted from these membrane fractions to be carried out. A second method of plasma membrane preparation was tested consisting first in the coating of the cell surface with positive colloidal silica which was stabilized by an anionic polymer. Then, and through differential centrifugations, plasma membrane fractions were easily obtained within less than 1 h, with a yield of 65% and an enrichment ratio of 7. The coating pellicle was quantitatively removed thus enabling any biochemical manipulation of the plasma membrane to be carried out. The lipids present in the plasma membrane of CHO cells were analyzed and are described, both in terms of headgroup and acyl chain composition.

Phosphorylation of membrane-associated proteins by phorbol esters in isolated bag cell neurons of Aplysia

Following brief synaptic stimulation, the bag cell neurons in the abdominal ganglion of Aplysia undergo a series of changes in electrophysiological and secretory properties that triggers egg laying behavior. Activation of protein kinase C appears to play an important role in these changes and, in particular, causes the unmasking of a new species of voltage-dependent calcium channel. We have now used isolated bag cell neurons maintained in cell culture to study changes in protein phosphorylation that are induced by exposure to an activator of protein kinase C. Primary cultures of bag cell neurons were labeled with 32P orthophosphate and then incubated with either tetradecanoyl phorbol 13-acetate (TPA), a potent activator of protein kinase C, or with an inactive phorbol ester. When protein extracts were separated with 2D electrophoresis approximately 100 phosphoproteins could be distinguished. Only four of these proteins, with molecular weights of 20, 32, 200, and 250 kD, underwent a reproducible increase in the extent of phosphorylation of at least twofold in response to TPA. TPA-induced changes in phosphate incorporation were blocked by pretreatment with the protein kinase C inhibitor H7. One of the TPA-regulated phosphoproteins was localized in a plasma membrane-containing fraction and was sensitive to trypsin treatment of intact cells, suggesting that it is a membrane protein with sites exposed to the extracellular medium. Two of the other TPA-regulated phosphoproteins may be associated with the inner face of the plasma membrane. Our results indicate that only a small number of proteins undergo a major change in phosphorylation state following the activation of protein kinase C in isolated bag cell neurons. One or more of these proteins may contribute to the unmasking of the calcium channels.

Mg2+ mediates the cell-substratum interaction of Arg-Gly-Asp-dependent HeLa cell collagen receptors

Three HeLa cell surface collagen receptors of apparent molecular mass 102/58, 87, and 38/33 kDa were eluted from gelatin-Sepharose with salt gradients or Arg-Gly-Asp-containing peptides. To understand how the collagen receptors are involved in HeLa cell spreading on collagen we investigated the effects of divalent cations and Arg-Gly-Asp-containing peptides on adhesion to gelatin, since HeLa cells behave similarly on both native type I collagen and gelatin substrata and also whether Arg-Gly-Asp-containing substrata would substitute for gelatin in facilitating cell spreading. Gly-Arg-Gly-Asp-Ser-containing peptides in solution inhibited HeLa cell spreading onto gelatin and promoted only partial HeLa cell spreading when bound to tissue culture plastic. Both partial spreading of HeLa cells on the Gly-Arg-Gly-Asp-Ser substratum and full spreading on gelatin was dependent on Mg2+, but not on Ca2+. Binding of the 102/58-, 87-, and 38/33-kDa collagen receptors to gelatin-Sepharose was increased fourfold in the presence of Mg2+, and subsequent elution of the collagen receptors and a 45-kDa collagen-binding protein not thought to be involved in HeLa cell spreading was achieved with EDTA. In contrast, affinity chromatography on Gly-Arg-Gly-Asp-Ser-Sepharose eluted predominantly the 45-kDa collagen-binding protein and the 38/33-kDa collagen receptor. In summary, the Mg2(+)-dependent interaction of the collagen receptors with the Arg-Gly-Asp sequence in collagen appears to be essential for the initial events in HeLa cell spreading but is not sufficient for full cell spreading.