The long-term objectives of the proposed project are to determine whether and how modulation of gap junctional intercellular communication is involved in the process of carcinogenesis.
The specific aim of the project is to test the hypothesis that blocking of communication between an initiated cell and surrounding normal cells is an important determinant in clonal expansion of the initiated cell, i.e., the tumor promotion process. Changes in intercellular communication will be examined during the process of cell transformation by measuring intercellular transfer of fluorescent dye which is microinjected into individual cells. Cell cultures, mainly BALB/c 3T3 and C3H 10T1/2 cell transformation systems, will be employed during the earlier phase of the project. Experiments are designed to answer following specific questions: (i) whether phorbol ester-mediated enhancement of cell transformation is related to the block of intercellular communication by the phorbol esters; (ii) whether so-called """"""""initiated cells"""""""" in which promotion is suppressed by retinyl acetate communicate with surrounding non-transformed cells, (iii) whether transformed cells communicate with each other and/or with surrounding non-transformed cells, and (iv) whether blocked intercellular communication also occurs during the process of promotion that is not triggered by phorbol esters. Variant cell lines that are sensitive or resistant to TPA-mediated enhancement of cell transformation (Syrian hamster embryo cells) and those that have different susceptibilities to UV- and chemically-induced transformation (BALB/c 3T3 cells) will be utilized to pursue these goals. The possibility of using the block of intercellular communication to screen tumor promoting agents will be examined. We plan to study molecular and biochemical mechanisms in detail. Our approach includes studies on (i) the molecular mechanisms by which phorbol esters inhibit the communication, with special emphasis on possible involvement of protein-kinase C activity, (ii) biochemical analysis of the factors involved in cell-cell recognition that influence gap-junctional communication, and (iii) possible oncogene involvement in blocking intercellular communication. Similar approaches will be applied to an in-vivo study using a rat-liver multistage carcinogenesis model. The microinjection technique coupled to electrophysiological measurements will be used to determine intercellular communication between preneoplastic nodules and/or hepatoma and surrounding normal cells.
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