Mechanisms of metastasis of tumor cells rely upon cell movement and protrusive activity. Thus a molecular understanding of amoeboid chemotaxis in metastatic cancer cells may identify new targets for therapeutic intervention. The rat mammary adenocarcinoma cell line MTLn3 provides a number of advantages for such studies. These cells grow easily in tissue culture and, when injected into the mammary fat pad of syngeneic Fisher 344 rats, form first a primary tumor and then lymph node and lung metastases. MTLn3 cells express roughly 50,000 EGF receptors per cell, while a nonmetastatic derivative termed MTC from the same original tumor does not express EGF receptors. Expression of the EGF receptor in the MTC cells increases metastatic ability without affecting primary tumor growth rate. This result combined with the literature correlating expression of EGF receptor family members with poor prognosis for cancer patients highlights the potential usefulness of analyzing chemotactic responses to EGF.
An MTLn3 cell oriented towards a pipet filled with a solution of 50 uM EGF (time in the top left corner, pipet is out of focus to the right). The cell crawled towards the pipet and changed direction when the pipet was moved (arrow marks the moving pipet on image 16:31:04); bar, 20 um. From Bailly et al., 1998.
Lamellipod extension occurs in response to uniform increases in EGF concentration. Cells were imaged before and after stimulation with 5 nM EGF. From Segall et al., 1996.
MTLn3 cells were plated on gold-coated glass coverslips which were patterned with hexadecanthiol and EGF6-thiol to generate 10 um lanes of adhesive substratum. The cells were stimulated with 5 nM EGF and changes in cell shape were monitored using phase contrast microscopy. Lamellipod extension over the nonadhesive surface is maximal at 4 minutes after stimulation. A net increase in cell length can be observed after 8 minutes. From Bailly et al., 1998.
IRM analysis of lamellipod extension and modifications of cell-substratum contacts after a homogeneous upshift of EGF. EGF stimulation triggered a lamellipod extension which was maximum around 3 minutes after stimulation. This extension was accompanied by the establishment of close contacts in the newly extended area. After 5 minutes, new focal contacts formed, which increased in size over the course of the experiment. Previously existing focal contacts were remodeled: some became diffuse and were no longer visible after 14 min. Focal contacts at tail disassembled during tail retraction From Bailly et al., 1998.
Motile primary tumor cells observed in an intact primary tumor 2.5 weeks postinjection. Time lapse imaging was performed. Arrow indicates the path of a series of cells moving between 20 - 34 minutes of a 60 minute imaging session. The main tumor mass remains stationary while the cells translocate. From Farina et al., 1998.
A tumor formed by GFP-tagged MTLn3 cells was visualized in situ. Although there was little movement by the fluorescent tumor cells, there are dark regions visualized upon the fluorescent tumor cell background that are the right size and move at about the speed expected for granulocytes. The dashed white lines indicate the path of blood vessels through the tumor, the arrows indicate areas where the putative immune system cells are seen.