ALTERED HOMOLOGOUS AND HETEROLOGOUS GAP-JUNCTIONAL INTERCELLULAR COMMUNICATION IN PRIMARY HUMAN LIVER-TUMORS ASSOCIATED WITH ABERRANT PROTEIN LOCALIZATION BUT NOT GENE MUTATION OF CONNEXIN-32

Gap-junctional intercellular communication (GJIC) in 20 primary human liver tumors with different degrees of malignancy has been studied at the functional and molecular levels. When GJIC capacity was determined by dye-transfer assay performed directly with freshly removed tumor t issue, significant reduction was found in all samples, regardless of t heir morphology. In addition, a selective lack of GJIC between tumor a nd surrounding non-tumorous cells was observed in some cases, probably due to the physical separation between them resulting from encapsulat ion of tumors. There was, however, no essential change in the level of expression of the major liver gap-junction protein, connexin (cx) 32, in liver tumors as measured by Northern and Western blot analyses. Im munohistochemical study revealed aberrant localization of cx 32 in the majority of malignant liver tumors. instead of cytoplasmic membrane l ocalization at intercellular contacts, cx 32 was detected mainly eithe r intracytoplasmically or in plasma membrane free from contact with ot her cells. We did not detect any mutation in the coding sequence of th e cx 32 gene from any of the human liver tumors we tested. Thus it is likely that the aberrant localization of cx 32 in tumor cells is due t o disruption of the mechanisms for establishment of this protein into gap-junction plaques, rather than to structural abnormality of the cx 32 protein itself. Another member of the connexin family, cx 43, not d etectable in non-tumorigenic hepatocytes, was expressed in several tum ors, especially in invasive areas, but was detected in only a few tumo r cells and was localized intracytoplasmically, suggesting that cx 43 protein is not involved in GJIC in the tumors. (C) 1994 Wiley-Liss, In c.