Somatic cell hybridization of human tumor samples

Could gastrointestinal tumor-initiating cells originate from cell-cell fusion in vivo?

Tumor-initiating cells (TICs) or cancer stem cells are believed to be responsible for gastrointestinal tumor initiation, progression, metastasis, and drug resistance. It is hypothesized that gastrointestinal TICs (giTICs) might originate from cell-cell fusion. Here, we systemically evaluate the evidence that supports or opposes the hypothesis of giTIC generation from cell-cell fusion both in vitro and in vivo. We review giTICs that are capable of initiating tumors in vivo with 5000 or fewer in vivo fused cells. Under this restriction, there is currently little evidence demonstrating that giTICs originate from cell-cell fusion in vivo. However, there are many reports showing that tumor generation in vitro occurs with more than 5000 fused cells. In addition, the mechanisms of giTIC generation via cell-cell fusion are poorly understood, and thus, we propose its potential mechanisms of action. We suggest that future research should focus on giTIC origination from cell-cell fusion in vivo, isolation or enrichment of giTICs that have tumor-initiating capabilities with 5000 or less in vivo fused cells, and further clarification of the underlying mechanisms. Our review of the current advances in our understanding of giTIC origination from cell-cell fusion may have significant implications for the understanding of carcinogenesis and future cancer therapeutic strategies targeting giTICs.

Polyethylene glycol significantly enhances the transfer of membrane immunoblotting

Poly(ethylene glycol)n is a group of water-soluble, hydrophobic, optically transparent and biomacromolecule-nondenaturing polymers. These properties have caused it be widely used for various purposes in the biological sciences. In this study, the effects of poly(ethylene glycol)n on protein preservation, electrotransferring, and immunoblotting from sodium dodecyl sulfate (SDS)-polyacrylamide gel onto polyvinylidene difluoride (PVDF) membrane have been systematically evaluated. After SDS-polyacrylamide gel electrophoresis, 30% poly(ethylene glycol)n may be applied to reversibly fix proteins within the gel more completely, differing from irreversible fixation produced by solutions such as trichloroacetic acid-sulfosalicylic acid or acetic acid-methanol systems. The intragel proteins, fixed by poly(ethylene glycol)n, can be electroblotted directly onto PVDF membranes in the presence of 30% poly(ethylene glycol)n. We have shown that treatment with poly(ethylene glycol)n may reduce background, raise signal-to-noise ratio, sharpen protein bands, and increase resolution, resulting in enhancement of the immunoblotting transfer. It is possible to visualize a few picograms of a single protein band, increasing the sensitivity of the method by 10- to 100-fold, as compared with standard immunoblotting techniques.

Genetic analysis of indefinite division in human cells: identification of four complementation groups

Hybrids obtained following fusion of normal human diploid fibroblasts with different immortal human cell lines exhibited limited division potential. This led to the conclusion that the phenotype of cellular senescence is dominant and that immortal cells arise as a result of recessive changes in the growth control mechanisms of the normal cell. We have exploited the fact that immortality is recessive and, by fusing immortal human cell lines with each other, assigned 21 cell lines to at least four complementation groups for indefinite division. A wide variety of cell lines was included in the study to determine what parameters, if any, would affect complementation group assignment. The results indicate that cell type, embryonal layer of origin, and type of tumor do not affect group assignment. There does not appear to be any correlation between expression of an activated oncogene and group assignment. However, all of the immortal simian virus 40-transformed cell lines studied (with the exception of one xerodermapigmentosum fibroblast-derived line) assign to the same group, indicating that this virus immortalizes various human cells by the same processes. The assignment of immortal human cells to distinct groups provides the basis for a focused approach to determine the genes important in normal growth regulation that have been modified in immortal cells.