Regulation of Thy-1 Gene Expression by the Methylation of the 5′ Region of Thy-1 Gene and Intracellular Regulatory Factors in Immature B Cells

In cμ− B220+ Thy-1− FL2-52-2, an immature B cell line transformed with a temperature-sensitive mutant of Abelson murine leukemia virus(ts OS-59), Thy-1 antigen expression was induced after the shift of the culture temperature from a permissive (35′ C) to a non-permissive temperature (39′ C), and a Thy-1+ subclone, FL2-52-2-1 was isolated by limiting dilution. Furthermore, since a population of Thy-1+FL2-52-2-1 lost Thy-1 antigen expression during culture at a non-permissive temperature, Thy-1− FL2-52-2-1-1 was isolated from the cultured cells. Methylation analysis by Southern blotting experiments showed that 5′ region of the Thy-1 gene was methylated in Thy-1− FL2-52-2 but demethylated in Thy-1+ FL2-52-2-1 and Thy-1− FL2-52-2-1-1. To determine whether or not there exist intracellular regulatory factors responsible for Thy-1 gene expression, Thy-1− allele was transfected into Thy-1− (Thy-1.2−) FL2-52-2 and Thy-1− FL2-52-2-1-1. The transfected Thy-1− allele was expressed in Thy-1− FL2-52-2, but not in Thy-1...