Computerized analysis of tumor cell interactions with extracellular matrix proteins, peptides, and endothelial cells under laminar flow

Integrin alpha4beta1/VCAM-1 pathway mediates primary adhesion of RAW117 lymphoma cells to hepatic sinusoidal endothelial cells under flow

Adhesion and stabilization of circulating tumor cells to endothelial cells in target blood vessels play an important role in the complex process of metastasis. We examined the cell surface receptors involved in the liver-metastatic adhesive interactions of murine RAW117 large-cell lymphoma cells to unstimulated hepatic sinusoidal endothelial cells (HSE) under physiological flow conditions. Flow cytometric analysis indicated that VCAM-1, ICAM-1 and PECAM-1 are constitutively expressed on the surfaces of both HSE and RAW117 cells. However, monoclonal antibody (mAb) blockade studies showed that ICAM-1 and PECAM-1 affected neither the attachment nor the stabilization step of the adhesion of RAW117 cells to HSE cell monolayers under flow. In contrast, RAW117 cells required a significantly lower shear stress to establish adhesion to HSE cells when VCAM-1 receptors on HSE cells were blocked with mAb. Furthermore, the presence of the anti-VCAM-1 mAb significantly decreased the extent of adhesion compared to that of the control, without affecting adherent cell stabilization times. Blocking the alpha4 integrin subunits present mainly on RAW117 cells produced similar results to those previously observed with anti-VCAM-1 mAb. Although constitutively present mainly on the surfaces of RAW117 cells, MAdCAM-1 and beta7 integrin subunit do not appear to play a role in either the arrest or stabilization of RAW117 cells on HSE cell monolayers. However, blocking the beta1 integrin subunit on the RAW117-H10 cells reduced adhesion to the same extent as anti-alpha4 and anti-VCAM-1 treatments. These observations suggest that an interaction of integrin alpha4/beta1 on RAW117 cells with liver endothelial VCAM-1 occurs during the early stages of the adhesion process and may be important in liver metastasis.

Beta1-integrin-mediated dynamic adhesion of colon carcinoma cells to extracellular matrix under laminar flow

To resist substantial wall shear stress exerted by blood flow metastasizing colon carcinoma cells have to form adhesive contacts with endothelial cells and subendothelial extracellular matrix (ECM). At secondary sites tumor cells have to stabilize these initial adhesive interactions to prevent detachment and recirculation. Previously we found that adhesion of colon carcinoma cells to ECM components under static conditions is mediated, in part, by various beta1-integrins. Since other malignant cells possess adhesive properties that are different under static and dynamic conditions, we analyzed human colon carcinoma cell adhesion under flow by decreasing the flow (wall shear stress, WSS) of cell suspensions and allowing cells to interact with collagen-coated surfaces in a laminar flow chamber. HT-29 colon carcinoma cells were used to study wall shear adhesion threshold (WSAT), dynamic adhesion rate (DAR) and adhesion stabilization rate (ASR). DAR was determined after a low flow period using a WSS set at 50% of WSAT. ASR was calculated 60 sec after reestablishment of high WSS. Glass slides were coated with collagen I (C I) or bovine serum albumin (BSA, negative control). In some experiments cells were pretreated with function-blocking anti-beta1 or nonspecific IgG. Rolling of cells occurred on C I- and BSA-coated surfaces at high WSS. By decreasing WSS cell sticking without definite adhesion was found, and cells stuck to BSA at WSS lower than that found for C I. Further decreasing WSS below WSAT enabled stable cell adhesion to C I, but only a few cells adhered to BSA. ASR was found to be 73% of primarily adherent cells (to C I). Pretreatment with anti-beta1 did not affect cell rolling but did inhibit cell sticking and adhesion completely, whereas nonspecific IgG was without effect. Activation of PKC using phorbol ester resulted in an increase of adhesive interactions under dynamic and static conditions, whereas its inhibition reduced adhesion. Adhesive interactions of HT-29 colon carcinoma cells with ECM-coated surfaces under laminar flow conditions occurred in various steps: (1) rolling, (2) sticking or initial adhesion, and (3) stabilization of adhesion. Under shear flow rolling of tumor cells on ECM-coated surfaces appeared to be mediated mainly by physical/mechanical and nonspecific surface-cell membrane interactions, whereas stabilized adhesion to ECM was specifically mediated by beta1-integrin binding to ECM components. PKC seems to be involved in the regulation of adhesion stabilization under static and flow conditions.

Interest of image processing in cell biology and immunology

Microscopy is a basic tool for cell biologists. Recent progress of electronics and computer science made powerful methodologies for digital processing of microscopic images easily available. These methods allowed impressive increase of the power of conventional microscopy. Dramatic image enhancement may be achieved by combination of filtering techniques, computer-based deblurring and contrast enhancement. Quantitative treatment of digitized images allows absolute determination of the density of different components of the observed sample, including antigens, intracellular calcium and pH. Morphometric studies are also greatly facilitated by image processing techniques. The capture of fast phenomena may be performed by transfer of small portion of microscopic images into computer memory as well as particular use of confocal microscopy. Finally, improved display of experimental data through coded colors or other procedures may enhance the amount of information that can be conveyed by visual examination of microscopical images. The purpose of the present review is to describe the basic principles of image processing and exemplify the power of this approach with a variety of illustrated applications to conventional, fluorescence or electron microscopy as well as confocal microscopy.

Differential adhesion of metastatic RAW117 large-cell lymphoma cells under static or hydrodynamic conditions: role of integrin alpha(v) beta3

RGD-containing substrates were used to study static and hydrodynamic adhesion of murine RAW117 large-cell lymphoma sublines with differential liver-metastatic potentials. Highly liver-metastatic RAW117-H10 cells had higher rates of static adhesion to vitronectin, fibronectin and (GRGDS)4 than poorly metastatic RAW117-P and moderately liver-metastatic RAW117-L17 cells. Under hydrodynamic conditions, adhesion stabilization was more rapid for H10 cells compared to P or L17 cells. Among the RGD peptides, only the polymeric RGD peptide (GRGDS)4 mediated strong static adhesion of H10 cells. Interestingly, all the RGD peptides mediated adhesion stabilization for H10 cells but still not for L17 or P cells under hydrodynamic conditions. Integrin alpha(v) beta3 was involved in stabilizing hydrodynamic adhesion to (GRGDS)4, monomeric RGD peptide R1, but was less important in static adhesion to monomeric RGD peptides. Differential adhesion to liver sinusoidal endothelial cell-derived extracellular matrix (H10 >> L17 > P) was observed under hydrodynamic but not static conditions. Integrin alpha(v) beta3 was also important in hydrodynamic adhesion to liver sinusoidal endothelial cell-derived extracellular matrix. We believe that strong static and hydrodynamic adhesion of H10 cells and their capability of altering adhesive behavior in response to fluid shear may contribute to liver metastasis.

Differential motility stimulation but not growth stimulation or adhesion of metastatic human colorectal carcinoma cells by target organ-derived liver sinusoidal endothelial cells

Liver is the most common distant metastatic site for colorectal cancers and when blood-borne colorectal cancer cells reach the liver, they first encounter hepatic capillary and sinusoidal endothelial cells. Thus we studied differences between highly (HT-29LMM) and poorly (HT-29P) liver-metastatic sublines of human colorectal cancer cells by examining the interactions between tumor cells and liver microvessel endothelial cells. Using hepatic sinusoidal endothelial (HSE) and lung microvessel endothelial (MLE) cell-conditioned medium we measured the growth and motility stimulating activities released from these endothelial cells and adhesion of these cancer cells to the endothelial cells. Differences in the ability of HSE-conditioned medium (HSE-CM) or MLE-conditioned medium (MLE-CM) to stimulate HT-29 cell growth were not observed. There was a small but significant increase in the rate of adhesion of highly metastatic HT-29LMM cells to HSE cell monolayers than poorly metastatic HT-29P cells, but there was no difference in adhesion to MLE cell monolayers. HSE-CM stimulated the motility of highly metastatic colorectal cancer cells to a greater extent than the poorly metastatic cells. Motility-stimulating activity for the colorectal cancer cell lines was not detected in MLE-CM. The HSE-CM motility-stimulating activity for human HT-29 cells was not removed using antibodies against hepatocyte growth factor (HGF/SF), complement component C3 or laminin, indicating that it is not related to these known liver-derived motility factors. The results suggest that the ability of highly metastatic HT-29LMM colorectal cancer cells to colonize the liver is related to their ability to respond to liver sinusoidal endothelial cell-derived motility factors and to a lesser degree to adhere to liver sinusoidal endothelial cells.