ALPHA-2-MACROGLOBULIN IS MAINLY PRODUCED BY CANCER-CELLS AND NOT BY HEPATOCYTES IN RATS WITH COLON-CARCINOMA METASTASES IN LIVER

Localization and production of alpha 2-macroglobulin (alpha 2M), a mul tifunctional binding protein with protease and cytokine scavenging pro perties, was studied in situ in rat Livers containing experimentally i nduced colon carcinoma metastases by means of immunocytochemistry and in situ hybridization methods. The study was performed to investigate whether alpha 2M production by hepatocytes plays a role in the defense against the growth of metastases on the basis of its protease inhibit ing capacity. It was found that colon cancer cells in all developmenta l stages of the metastases contained large amounts of messenger RNA (m RNA) of alpha 2M but hardly any alpha 2M protein, Cancer cells in cult ure contained large amounts of both mRNA and protein of alpha 2M. In c ontrast, stromal cells and liver cells did not show positivity for alp ha 2M mRNA above background levels, The exception was a few layers of hepatocytes around the latest stage of metastases. Hepatocytes contain ed both alpha 2M mRNA and protein only when Kupffer cells were present , indicating that alpha 2M mRNA production was induced via Kupffer cel ls. On the other hand, alpha 2M protein was found in high amounts in t he sinusoids and stroma of all metastases, irrespective of their devel opmental stage. Increased levels of alpha 2M could not be detected in serum in all but one rat tested (n = 8). It is concluded that producti on of alpha 2M by hepatocytes occurs only around the latest developmen tal stage of metastases and that alpha 2M does not play a significant role in the defense against metastatic cancer growth in rat Liver. In contrast, cancer cells produce and secrete large amounts of alpha 2M, which seems to be Linked with their tumorigenicity. We suggest that th is alpha 2M captures cytokines rather than proteases by complex format ion, These complexes were observed using immunocytochemical staining f or alpha 2M protein indicating that it was captured by either stromal cells, sinusoidal cells, or hepatocytes that are in direct contact wit h cancer cells, Therefore, changes in serum levels of alpha 2M were li mited, indicating that these levels do not reflect local production an d effects of alpha 2M.