Human globin gene expression in hybrid 2S MEL × human fibroblast cells

A somatic cell hybrid line, called M11-X, was developed in order to study the expression and regulation of the human β-like globin genes in a mouse erythroid environment. M11-X cells were obtained by fusing the human fibroblast cell line GM3552 (which contains the translocation chromosome t(11;X) that carries the human β-like globin genes) with hypoxanthine phosphoribosyltransferase (HPRT)-negative tetraploid (2S) mouse erythroleukemia (MEL) cells. After induction with 5 mM hexamethylene bisacetamide (HMBA), these cells contain approximately 300-600 copies per cell of correctly initiated, processed, and terminated human β-globin mRNA; however, neither human ε-nor γ -globin mRNAs were detected. Carboxymethylcellulose chromatography followed by SDS-polyacrylamide gel electrophoresis and Western blotting revealed that normal human β-globin protein was also present. These results suggest that the human β-globin gene, when present in mouse erythroid cells, can be transcribed and its mRNA translated into normal products, but at a much lower level than the mouse β-globin genes. Analysis of the frequency of cytosine methylation near the human γ-globin genes indicated that these genes are heavily methylated in M11-X cells. The inability to express the human γ-globin genes of these cells might be accounted for, at least in part, by DNA methylation.