Restored invasion of mouse MO4 cells into chick heart in vitro through mutual conditioning at reduced temperature

Inositol-C2-PAF acts as a biological response modifier and antagonizes cancer-relevant processes in mammary carcinoma cells

PURPOSE

Previous studies have identified alkyl-phospholipids as promising compounds for cancer therapy by targeting constituents of the cell membrane and different signaling pathways. We previously showed that the alkylphospholipid Inositol-C2-PAF inhibits the proliferation and migration of immortalized keratinocytes and the squamous carcinoma-derived cell line SCC-25. Here, we investigated the effect of this compound on growth and motility as well as its mode of action in mammary carcinoma-derived cell lines.

METHODS

Using BrdU incorporation and haptotactic cell migration assays, we assessed the effects of Inositol-C2-PAF on MCF-7 and MBA-MB-231 cell proliferation and migration. The phosphorylation status of signaling molecules was investigated by Western blotting as well as indirect immunofluorescence analysis and capillary isoelectric focusing.

RESULTS

We found that Inositol-C2-PAF inhibited the growth as well as the migration in MCF-7 and MBA-MB-231 cells. Furthermore, we found that this compound inhibited phosphorylation of the protein kinase Akt at serine residue 473, but had no impact on phosphorylation at threonine 308. Phosphorylation of other kinases, such as Erk1/2, FAK and Src, which are targeted by Inositol-C2-PAF in other cells, remained unaffected by the compound in the mammary carcinoma-derived cell lines tested. In MCF-7 cells, we found that IGF-1-induced growth, as well as phosphorylation of Akt^S473, mTOR and the tumor suppressor pRB, was inhibited in the presence of Inositol-C2-PAF. Moreover, we found that in these cells IGF-1 had no impact on migration and did not seem to be linked to full Akt activity. Therefore, MCF-7 cell migration appears to be inhibited by Ino-C2-PAF in an Akt-independent manner.

CONCLUSION

The antagonistic effects of Inositol-C2-PAF on cell migration and proliferation are indicative for its potential for breast cancer therapy, alone or in combination with other cytostatic drugs.

Altered glycosylation in Madin-Darby canine kidney (MDCK) cells after transformation by murine sarcoma virus

The changes in glycosylation of an immortalized epithelial cell line (MDCK) before and after progression towards a more malignant phenotype have been studied. The parental MDCK-3 cells were immortalized after long-term passage in vitro and have shown no tendency for spontaneous acquisition of malignancy-related phenotypes such as tumorigenicity, invasion and metastasis. They conserved morphological and functional characteristics of the epithelial tissue of origin. The ras-MDCK cells acquired the fully malignant phenotype after transformation with a Harvey murine sarcoma virus; they were immortalized, invasive in vitro and produced invasive and also metastatic tumors after subcutaneous injection into nude mice. Using immobilized lectins and gel chromatography, before and after liberation of O-linked glycans from the peptide moieties and also after removal of terminal sialic acid, we have found differences in the glycosylpeptides of both whole cells and cell surface trypsinates from ras-MDCK cultures as compared to the parental MDCK-3 cultures: (i) more sialic acid in the N-linked tri- and tetra-antennary structures; (ii) more fucosylation in the N-glycosylpeptides; (iii) more bi-antennary N-glycosylpeptides and less O-linked glycans; and (iv) a lower molecular weight of the O-linked glycans probably due to a decreased sialylation. It is concluded that alterations in sialylation and fucosylation of the cell surface exposed glycans accompanied progression of MDCK-3 cells towards a more malignant phenotype.

Decreased fucose incorporation in cell surface carbohydrates is associated with inhibition of invasion

Invasion of malignant MO4 cells into embryonic chick heart fragments in an organ culture assay was arrested for at least 7 days when the temperature was lowered to 28 degrees C. Prolonged culturing of MO4 cells at 28 degrees C on tissue culture substrates showed no recuperation of fucose incorporation into cell surface glycopeptides. However, invasion was restored after 10 days of organ culture in confrontation with chick heart tissue at 28 degrees C. A histoautoradiographic study showed that the regained capability to invade was accompanied by an increase in fucose labeling of the MO4 cells in the invading areas. At 28 degrees C the incorporation of [3H]fucose into total cell protein was drastically reduced, whereas [3H]leucine incorporation as a measure for protein synthesis was less affected. Cell surface glycopeptides, metabolically labeled with either fucose or glucosamine at 28 degrees C, showed a time-dependent decrease in the incorporation of fucose but not of glucosamine and no changes in overall size distribution. Low temperature did not reduce fucosyltransferase activity but the relative accumulation of fucose-1-P suggested inhibited conversion towards GDP-fucose. Moreover, mouse L cells which were incapable of invading chick heart tissue appeared also deficient in fucose incorporation, owing to low levels of fucosyltransferase activity. According to the results, fucosylation of surface carbohydrates may be required for invasive capacity and restored in MO4 cells invading at 28 degrees C by metabolic cooperation with the host tissue.