Growth Inhibition, Enhancement of Intercellular Adhesion, and Increased Expression of Carcinoembryonic Antigen by Overexpression of Phosphoinositides‐specific Phospholipase C β1 in LS174T Human Colon Adenocarcinoma Cell Line

By using a retrovirus‐derived system we generated derivatives of the human colon adenocarcinoma cell line LS174T (ATCC CL 188) that stably overexpress a full‐length cDNA encoding the β1 isoform of bovine phosphoinositides‐specific phospholipase C (PI‐PLC). This was confirmed by the elevated levels of catalytic activity to release phosphoinositides from phosphatidylinositol (PI‐PLC) or phosphatidylinositol‐bis‐phosphate (PIP(2)‐PLC), and the enhanced expressions of messenger RNA and protein. PI‐PLC β1 overexpresser clones grew to form cell clumps floating in liquid medium, whereas the pMV7‐introduced control clones displayed morphologic characteristics that were very similar to those of the parent LS174T cell line. Three individual PI‐PLC β1 overexpresser cell lines displayed increased doubling time (18.0 h, 21.5 h, and 23.8 h) when compared with 4 individual pMV7‐introduced control cell lines (13.1 h, 10.7 h, 12.9 h, and 9.3 h). Anchorage‐independent growth ability in soft agar medium was dramatically suppressed by overexpression of PLC β1, and the ability of PLC‐overproducer clones to form aggregates when cultured in liquid medium was dramatically enhanced when compared with that of pMV7‐introduced control clones. Tumorigenicity of PLC β1‐overproducers was much weaker than that of vector‐transduced control clones. The spontaneous release of carcinoembryonic antigen from PLC β1‐overproducer clones was much higher than that from pMV7 control clones. The ability of PLC β1‐overproducer clones to form aggregates during suspension culture was much stronger than that of the control clones. These results provide the first evidence that elevated levels of endogenous PI‐PLC β1 suppress tumor cell growth, but enhance the ability to form cell aggregates and to release carcinoembryonic antigen, an intercellular adhesion molecule.