Minipodia, novel structures for extension of the lamella: a high-spatial-resolution video microscopic study

Expression of prohibitin 3' untranslated region suppressor RNA alters morphology and inhibits motility of breast cancer cells

The prohibitin 3' untranslated region (3'UTR) belongs to a novel class of non-coding regulatory RNAs. It arrests cell cycle progression by blocking G1-S transition in breast and other cancers. Our previous studies comparing MCF7 derived clones constitutively expressing a common allelic form of prohibitin RNA (UTR/C) to various controls demonstrated that it functions as a tumor suppressor. Here, we further characterized the morphology and motility of these transgenic breast cancer cells when grown in cell culture and on nude mice. In contrast to empty vector (EV) cells, UTR/C cells were observed to grow in an organized manner with more cell-cell contact and differentiate into structures with a duct-like appearance. Computer assisted cytometry to evaluate differences in nuclear morphology was performed on UTR/C and EV tissues from nude mice. Receiver operator curve areas generated using a logistic regression model were 0.8, indicating the ability to quantitatively distinguish UTR/C from EV tissues. Keratinocyte growth factor-induced motility experiments showed that migration of UTR/C cells was significantly reduced (80-90%) compared to EV cells. Together, these data indicate that this novel 3'UTR influences not only the tumorigenic phenotype but also may play a role in differentiation and migration of breast cancer cells.

Keratinocyte growth factor-induced motility of breast cancer cells

Endogenous growth factors and cytokines are known to have a major influence on the progression, motility and invasiveness of tumor cells. We have reported previously that conditioned media from mouse fibroblasts increases the motility of breast cancer cells. Further, we determined that keratinocyte growth factor (KGF) was an active factor from mouse fibroblasts responsible for most of the motility response in breast cancer cells. The present study examined the effect of Human KGF on the motility of estrogen receptor (ER)-positive and ER-negative human breast cancer cell lines in culture using time-lapse videomicroscopy to quantify cell motility. In the present study we observed that recombinant human KGF enhanced several parameters of cellular motility in ER-positive cells but not in ER-negative cell lines. Further, we observed that the level of KGF receptor (KGFR) expression in ER-positive cells was much greater than in the ER-negative cell lines. The motility response to KGF was found to be both dose-and time-dependent. Of the three ER-positive breast cancer cell lines tested. MCF-7 cells were the most responsive to KGF stimulation. Finally, MCF-7 cells grown in estrogen-depleted media did not respond to KGF. These results suggest that KGF from stromal tissue surrounding a primary tumor mass can enhance tumor cell motility and may be an early signal in the progression of breast cancer cells to a more motile and metastatic phenotype. Thus, KGF, KGFR and/or the KGF signaling pathway may be important therapeutic targets for the treatment or prevention of breast cancer metastasis.

TGF-beta 1 reverses PDGF-stimulated migration of human aortic smooth muscle cells in vitro

Platelet-derived growth factor (PDGF) and transforming growth factor beta-1(TGF-beta 1) were tested separately or together for the ability to stimulate migration of human aortic vascular smooth muscle cells (VSMC). PDGF (10 ng/ml) stimulated migration of VSMC over a 48-h period. TGF-beta 1 (10 ng/ml) had no effect on migration during the same period. VSMC exposed simultaneously to both TGF-beta 1 and PDGF exhibited diminished migration (50%) when compared to cells treated only with PDGF. Cells that migrated in the presence of PDGF possessed short actin cables that extended from cellular processes at the leading edge of migrating cells; focal adhesions containing the alpha v beta 3/beta 5 integrins localised to the same region. Cells grown in the presence of TGF-beta 1 exhibited long, intensely stained actin filaments that spanned the entire length of the cell and were similar to untreated control VSMC. Focal adhesions containing alpha v beta 3/beta 5 distributed evenly on the basal surface in both TGF-beta 1-treated cells and control cultures. Cellular responses to PDGF were mitigated when TGF-beta 1 was present in the culture medium. VSMC grown in the presence of both PDGF and TGF-beta 1 exhibited elongated actin filaments that were similar to nonmotile TGF-beta 1-treated cultures. Concomitant exposure of VSMC to PDGF and TGF-beta 1 resulted in focal adhesions that distributed evenly on the lower cell surface. This study suggests that TGF-beta 1 can partially reverse the stimulatory effect of PDGF on VSMC migration in vitro by modifying the actin cytoskeleton and the distribution of the alpha v beta3/beta 5 integrins.

Tyrosine phosphorylation of paxillin and focal adhesion kinase during insulin-like growth factor-I-stimulated lamellipodial advance

In the current studies, we examined whether focal adhesion kinase (FAK) and paxillin play a role in insulin-like growth factor-I (IGF-I)-stimulated morphological changes in neuronal cells. In SH-SY5Y human neuroblastoma cells, 10 nM IGF-I enhanced the extension of lamellipodia within 30 min. Scanning electron microscopy and staining with rhodamine-phalloidin showed that these lamellipodia displayed ruffles, filopodia, and a distinct meshwork of actin filaments. Immunofluorescent staining identified focal concentrations of FAK, paxillin, and phosphotyrosine within the lamellipodia. Immunoprecipitation experiments revealed that FAK and paxillin are tyrosine-phosphorylated during IGF-I-stimulated lamellipodial extension. Maximal phosphorylation of FAK and paxillin was observed 15-30 min after the addition of 10 nM IGF-I, whereas maximal IGF-I receptor phosphorylation occurred within 5 min. FAK, paxillin, and IGF-I receptor tyrosine phosphorylation had similar concentration-response curves and were inhibited by the receptor blocking antibody alphaIR-3. These results indicate that FAK and paxillin are tyrosine-phosphorylated during IGF-I-stimulated lamellipodial advance and suggest that the tyrosine phosphorylation of these two proteins helps mediate IGF-I-stimulated cell and growth cone motility. These responses contrast directly with recent reports showing insulin-stimulated dephosphorylation of FAK and paxillin.

Actin-dependent motile forces and cell motility

Force arising from actin polymerization and myosin activity drives a number of different actin-based cell movements. Several new reports support previous data suggesting that actin polymerization drives lamellipodial protrusion and bacterial propulsion, and one report describes a more indirect role for actin assembly in axonal elongation. The major new findings of the past year concerning possible motility roles for myosin describe myosin-driven protrusion of cell margins.