Matrix and laminin synthesis in MDCK cells in vitro

Raf kinase inhibitor protein positively regulates cell-substratum adhesion while negatively regulating cell-cell adhesion

Raf kinase inhibitor protein (RKIP) regulates a number of cellular processes, including cell migration. Exploring the role of RKIP in cell adhesion, we found that overexpression of RKIP in Madin-Darby canine kidney (MDCK) epithelial cells increases adhesion to the substratum, while decreasing adhesion of the cells to one another. The level of the adherens junction protein E-cadherin declines profoundly, and there is loss of normal localization of the tight junction protein ZO-1, while expression of the cell-substratum adhesion protein beta1 integrin dramatically increases. The cells also display increased adhesion and spreading on multiple substrata, including collagen, gelatin, fibronectin and laminin. In three-dimensional culture, RKIP overexpression leads to marked cell elongation and extension of long membrane protrusions into the surrounding matrix, and the cells do not form hollow cysts. RKIP-overexpressing cells generate considerably more contractile traction force than do control cells. In contrast, RNA interference-based silencing of RKIP expression results in decreased cell-substratum adhesion in both MDCK and MCF7 human breast adenocarcinoma cells. Treatment of MDCK and MCF7 cells with locostatin, a direct inhibitor of RKIP and cell migration, also reduces cell-substratum adhesion. Silencing of RKIP expression in MCF7 cells leads to a reduction in the rate of wound closure in a scratch-wound assay, although not as pronounced as that previously reported for RKIP-knockdown MDCK cells. These results suggest that RKIP has important roles in the regulation of cell adhesion, positively controlling cell-substratum adhesion while negatively controlling cell-cell adhesion, and underscore the complex functions of RKIP in cell physiology.

Polymer design for corneal epithelial tissue adhesion: pore density

A porous polymer is required to sustain corneal epithelial tissue on the anterior surface of an implantable contact lens (corneal onlay). Porosity creates topography on the polymer surface and, if defined, this can be manipulated to elicit a particular tissue response. Previous work identified pores of 100-nm diameter to be the critical size of a discontinuity in a polymer surface to facilitate the migration, stratification, and sustained adhesion of corneal epithelial tissue. Now we address the issue of pore density. Corneal epithelial tissue was grown for 21 days on nonporous polycarbonate and polycarbonate track-etched with pores 100-nm diameter with pore densities ranging from 0.27 and 14.4% of the total polymer surface area. Histology was used to score epithelial structure, and electron microscopy was used to quantitate the formation of adhesive structures (basal lamina and hemidesmosomes) at the tissue-polymer interface. Data showed that epithelial tissue stratified and epithelial adhesive structures formed on polycarbonate surfaces with pore densities between 0.52 and 14.4% inclusive. This means that epithelial tissue can be maintained on a polymer where up to 14.4% of the surface is dedicated to small discontinuities in the form of pores 100-nm diameter. These figures can be used to specify the design of a polymer for applications requiring epithelial cover.

Renal cell cultures for the study of growth factor interactions underlying kidney organogenesis

The present study was performed in four renal cell lines to evaluate their capability to: (1) produce and express transforming growth factor alpha (TGFalpha), its respective receptor, the epidermal growth factor receptor (EGFr) and the small G protein, RhoA, and (2) exhibit morphogenetic properties when grown on Matri-cell substrates. The cell lines were derived from normal (Madin-Darby canine kidney cells), embryonic (SK-NEP-1 and 293 cells), and cancerous (human renal adenocarcinoma cells) kidneys. TGFalpha messenger ribonucleic acid, evaluated by a nonradioactive in situ hybridization technique, was found to be expressed in all the cell lines. Large amounts of TGFalpha peptide were observed in all four cell lines, while EGFr was highly expressed only in cancerous ACHN and embryonic-tumor SK-NEP-1 cells. RhoA peptide was found in appreciable amounts in SK-NEP-1 and 293 cells (compared to the other two cell lines). The morphogenetic properties of the four cell lines were assessed, by culturing them on Matri-cell dishes: SK-NEP-1 cells alone were found to grow in three-dimensional structures forming clusters and worm-like cellular aggregates. This feature was displayed by SK-NEP-1 cells but not by the other three cell lines, and may be connected with the contemporary presence of RhoA, EGFr, and TGFalpha found in significant amounts only in the SK-NEP-1 cell line.

Cell-substrate and cell-cell interactions differently regulate cytoskeletal and extracellular matrix protein gene expression

In this study, cellular events during tissue formation were investigated at the mRNA level using the Northern blot technique. The levels of expression of mRNAs encoding specific proteins (beta-actin, fibronectin, and laminin) during tissue formation on tissue culture dishes were quantitatively assessed using a Northern blot technique with autoradiography. The level of beta-actin mRNA increased with incubation time and reached a maximal level near the confluent state, followed by reduced beta-actin mRNA expression at a later stage of tissue formation. The time course of beta-actin mRNA expression corresponded well to the time course of morphologic changes and cytoskeletal organization in adherent cells. Expression of the mRNAs encoding the extracellular matrix proteins fibronectin and laminin was initiated at the proliferation stage. After maximum expression levels of these two mRNAs were reached at the confluent stage, a gradual decrease in their expression levels was seen during long-term culture. Expression patterns of mRNAs encoding cytoskeletal and extracellular matrix proteins strongly depended on the type of artificial substrates used; a mRNA expression pattern similar to that observed during tissue formation on tissue culture dishes was observed on a cell-adhesive substrate during tissue formation, whereas reduced expression was seen during tissue formation on a less adhesive substrate. Thus, the dynamic changes occurring during tissue formation were quantified to investigate the roles of artificial substrates in tissue formation at the mRNA level.

Differential expression of integrin alpha subunits supports distinct roles during lung branching morphogenesis

Epithelial branching morphogenesis is a process by which a continuous epithelium, embedded in mesenchyme, forms tubules that extend and branch into the surrounding mesenchyme. The morphogenetic process is responsible for the architecture of many organs including the lung. Proper expression and function of extracellular matrix (ECM) molecules, such as collagens and laminins, are necessary for branching to occur normally. However, little is known about the role of epithelial cell surface molecules that mediate epithelial-matrix interactions during this process. We have studied the expression patterns of cell surface collagen and laminin integrin receptor alpha subunits, alpha 1, alpha 2, alpha 3, and alpha 6, in relation to that of collagen and laminin during lung branching morphogenesis. The alpha 1 integrin subunit was present on endothelia and smooth muscles around airways and large blood vessels. The mesenchyme expressed high levels of alpha 2 and alpha 6 but not alpha 3, whereas the epithelium expressed all three integrin subunits. In contrast to the widespread epithelial expression of alpha 3 and alpha 6, the epithelial expression of alpha 2 was restricted to branch tips. By performing in situ hybridization and immunofluorescence on serial sections, we found that alpha 2 protein expression on the epithelium correlated spatially and temporally with high level expression of collagen IV and laminin-1 mRNAs, suggesting that the alpha 2-expressing epithelial cells were in the process of producing and assembling their collagen and laminin matrices. While the expression of alpha 3 and alpha 6 on all lung epithelia suggests that these integrins may be important to lung epithelial development, the unique expression pattern of the alpha 2 subunit suggests that the alpha 2 beta 1 integrin may be important at branch tips either in the process of collagen/laminin synthesis and assembly or extension of the epithelial tubules into the mesenchyme.

Disruption of microfilaments alters laminin synthesis but not laminin trafficking in NHEK in vitro

Laminin synthesis and deposition are concomitant with the development of a basal lamina between the human epidermis and the underlying dermis. One of the challenges in tissue engineering of human epidermal models is to develop substrates and conditions that encourage the development of a basement membrane. The purpose of this study was to determine if actin filaments and/or microtubules are involved in the synthesis/secretion of laminin by normal human epidermal keratinocytes (NHEK) in vitro. NHEK synthesize and secrete laminin subunits B1, B2, and M but little, if any, of laminin subunit A. Data indicate that disruption of microfilaments by the destabilizing agent, cytochalasin D, had no apparent effect on the relative synthesis rates of most cytosolic proteins as revealed by one-dimensional sodium dodecyl sulfate (SDS) gel electrophoresis. This drug, however, increased laminin B2 synthesis several fold over untreated controls. This enhanced synthetic rate was independent of the type of collagen matrix on which the NHEK were grown. Similar increases in synthesis of the M and B1 laminin chains were not observed. To determine if this increase in synthesis lead to increases in laminin B2 secretion, laminin B2 was immunoprecipitated from both the apical and basal domains of NHEK cells grown on microporous membranes. While more laminin B1, B2, and M were secreted basally than apically, an observation consistent with laminin's role in basal lamina formation, cytochalasin D had no apparent effect on either basal or apical laminin B2 secretion. Experiments with the microtubule destabilizer, nocodazole, showed no similar effects on laminin synthesis and/or secretion. We conclude that (a) disruption of the actin network in NHEK selectively increases the synthesis of laminin B2, (b) the secretion of laminin B2 from NHEK cells is not governed by either the microfilamentous cytoskeleton or the amount of laminin synthesized by NHEK, and (c) disruption of the microtubular network does not alter laminin synthesis or secretion.

Modulation of adhesive properties of DEAE-dextran with laminin

Human squamous epithelial cells produce lower amounts of laminin and fibronectin when cultured on DEAE-dextran than when cultured on gelatin-coated polystyrene (Biotechnol. Bioeng., 33:1235). The epithelial cells also spread much more slowly on DEAE-dextran than they do on gelatin-coated polystyrene. To determine if the low level of matrix production by cells grown on DEAE-dextran contributed to the slowness of cell spreading on this substrate, microcarriers made from DEAE-dextran were treated with exogenous laminin (10 micrograms/cm2 of surface area) and then examined for ability to support cell adhesion. Squamous epithelial cells spread as rapidly on the laminin-treated DEAE-dextran as they did on gelatin-coated polystyrene (much more rapidly than on untreated DEAE-dextran). This indicates 1) that laminin can bind to DEAE-dextran in a fashion that is biologically usable by anchorage-dependent cells, and 2) that when laminin is bound to DEAE-dextran, the failure of squamous epithelial cells to rapidly spread is overcome. These data support the hypothesis that failure of the cells to synthesize an intact extracellular matrix on DEAE-dextran is responsible, at least in part, for the slowness with which cells spread on this substrate.