A study of desmosomes in colorectal carcinoma.

Desmosomes are adhesive junctions of epithelial cells. Their expression may be altered or lost in carcinomas resulting in reduced cellular adhesiveness. The desmosomes of colorectal carcinomas have been studied by fluorescent antibody staining, immunoblotting and electromicroscopy. A series of 58 malignant specimens, comprised of primary tumours and metastases, were desmosome positive. There was no indication of a comparative reduction in desmosome expression that might give rise to reduced adhesiveness of tumour cells, although loss of polarised junctional distribution in poorly differentiated tumours might have such a consequence. Western blotting analysis of colorectal cancers and cultured carcinoma cells identified desmosomal polypeptides dp1 + 2, dg1 and dg2 + 3 with similar relative molecular weights to normal homologues. In addition, a polypeptide of 140,000 was recognised only in malignant epithelium by anti-dg2 + 3 antiserum. The significance of this polypeptide is not understood. Tumours and uninvolved epithelium were exposed to low extracellular [Ca2+] to test whether tumour desmosomes were of reduced stability. This caused much cellular degradation in tumours but some viable cell clumps possessed desmosomes resistant to disruption by low [Ca2+]. Desmosomes may thus have a positive role in metastasis by maintaining intercellular adhesion between metastasising cells.