Suppression and reexpression of human intestinal-like alkaline phosphatase in intraspecific hybrids

Expression of the gene locus which codes for a form of human intestinal alkaline phosphatase (ALP) has been analyzed in intraspecific somatic cell hybrids. Hybrids were constructed between D98/AH-2, a line of HeLa which ectopically synthesizes high levels of this ALP isozyme, and three different nonintestinal ALP-producing diploid lines. In chromosomally complete hybrids, expression of the ALP isozyme was initially suppressed, but on extended culture, reexpression occurred, as did limited chromosome loss. Results from extensive subcloning experiments showed that events leading to reexpression occurred at high frequency, and this ALP reexpression appeared to confer some selective advantage, direct or indirect, on the cells. In the fibroblast hybrids, reexpression of the intestinal-like ALP was always accompanied by new, high-level expression of liver/bone/kidney ALP, the product of a separate ALP gene locus. Thus expression of the one ALP locus is not excluded and, in fact, appears to be promoted by expression of the other in these cells.