Morphology of peritumoral proteoglycan alterations in the rabbit mesentery invaded by V2 carcinoma cells.

After intraperitoneal implantation into Swiss Silver rabbits, V2 rabbit carcinoma cells invade the mesentery where they form nodules of different size and texture: compact (less than 120 microns in diameter), loose (120-250 microns) and mixed (above 200 microns). Together with tumor development, certain changes take place in the loose connective tissue of the mesentery. Application of TEM, together with use of safranin O, has shown that, in areas free of tumor growth, collagen bundles become thick and heavy and proteoglycan density is increased. Concurrently, the number of fibrocytes, now transformed to fibroblasts, increases. Small, compact nodules are surrounded by a concentrically arranged extracellular matrix. Its overall density is similar to that of nodule-free areas. In the immediate vicinity of large, loose nodules, all constituents of the extracellular matrix disappear. Adjacent connective tissue is partly destroyed but still contains collagen fibers and proteoglycans. These findings suggest the following: The presence of V2 carcinoma cells induces marked alterations in the structured and non-structured components of the extracellular matrix. These changes are, at the same time, progressive and regressive and the occurrence of one or the other depends on local tumor progression. Progressive alterations may result from an increased activity of fibroblasts. Since degradative effects, on the other hand, are only seen in the immediate vicinity of larger tumor aggregates, it is assumed that a minimal number of tumor cells is essential for destruction of extracellular matrix.

Morphological studies on V2 carcinoma invasion and tumor-associated connective tissue changes in the rabbit mesentery.

The mesentery is a duplicature of the peritoneum consisting of loose connective tissue and covered on both sides by mesothelium. Rabbit V2 carcinoma cells implanted i.p. adhere to the mesenteric surface between contracted mesothelial cells. While invasion from these sites sets in, progressive changes of the connective tissue, reflecting fibroblast stimulation, become apparent and comprise multiplication of connective tissue cells, transformation of fibrocytes into fibroblasts, and enhanced production of fibrillar and nonfibrillar constituents of the extracellular matrix. Tumor invasion into this increasingly dense tissue proceeds in 2 ways. (a) Single cells penetrate into and locomote within the interior, where they divide and give rise to nodules which become surrounded by zones of tissue destruction. (b) Proliferation of surface-attached tumor cells results in the formation of nodules which, preceded by zones of tissue damage, extend into the interior. While evidence for lytic effects in the microenvironment of single tumor cells is lacking, degradation of the fibrillar extracellular matrix is regularly found around tumor nodules and indicates a collective lytic action achieved by tumor cells and, possibly, host cells. These morphological findings are discussed in relation to published bio- and histochemical data on spread of the V2 carcinoma.

Cytoskeletal organization in locomoting cells of the V2 rabbit carcinoma.

The relationship between the organization of cytoskeletal elements and locomotory activity was studied in single cells of the V2 rabbit carcinoma. Like migratory fibroblasts, and unlike colony-forming epithelial cells, these cells show a pronounced horizontal polarization, and develop a large lamella at their leading front. With affinity-purified antibodies and a combination of light and electron microscopic techniques, actin and alpha-actinin (but not myosin and tropomyosin) were found highly concentrated within the marginal region of the leading lamella, both in ruffles and in the underlying zone of contacts with the substratum. Close contacts prevailed in the locomotory cells and small focal contacts developed only in cells detaching from others. Focal contacts always contained small microfilament bundles. Reorganization of actin filaments is suggested as the fundamental event for the dynamic contact formation of the leading lamella. Large microfilament bundles (stress fibers) were absent in all stages of locomotion. Since locomotory behavior and shape changes of V2 cells are the same on glass as on the surface of a natural membrane, the rabbit mesentery, organization and distribution of contractile elements of cultured V2 cells probably reflect the in vivo situation.