Stable transfer and restricted expression of a cloned class I gene encoding a secreted transplantation-like antigen.

Abstract

The identification of a unique major histocompatibility complex class I gene, designated Q10, which encodes a secreted rather than a cell surface antigen has led to questions regarding its potential role in regulating immunological functions. Since the Q10 gene is specifically activated only in the liver, we sought to define the molecular mechanisms which control its expression in a tissue-specific fashion. Results obtained by transfection of the cloned Q10 gene, either in the absence or presence of a heterologous transcriptional enhancer, into a variety of cell types of different tissue derivations are consistent with the Q10 gene being regulated at two levels. The first is by a cis-dependent mechanism which appears to involve site-specific DNA methylation. The second is by a trans-acting mechanism which would include the possibility of an enhancer binding factor. The ability to efficiently express the Q10 gene in certain transfected cell lines offers an opportunity to obtain this secreted class I antigen in quantities sufficient for functional studies; this should also make it possible to define regulatory sequences which may be responsible for the tissue-specific expression of Q10.

Liver-specific expression of a Qa-encoded class I gene is associated with DNA hypomethylation.

“…Recently, a study was published on the state of methylation of the Q10 gene transformed in tissue culture cell lines (1). That study found no direct correlation between DNA methylation and Q10 expression; a mixture of methylated and unmethylated sequences was found in both expressing and nonexpressing cell lines.…”

De NovoMethylation of an MHC Class I Transgene Following Transformation with Human Adenoviruses Is Not Correlated with Its Altered Expression

“…These results could not rule out the possibility that unique sites in the PD1 sequence that are methylated are important for the expression of the gene in Adl2-transformed cells. Such a case was observed by Barra et al (1985), who studied methylation and expression of Q10 genes in a mouse hepatoma cell line. In this cell line, methylation of a site within the third intron has been correlated with loss of Q10 transcriptional activity.…”

Genetic engineering of an H-2Dd/Q10b chimeric histocompatibility antigen: purification of soluble protein from transformant cell supernatants.

“…These differ from the classical class I antigens in that (i) their tissue distribution is more restricted; (ii) they are less polymorphic; and (iii) their function is unclear. One of the Qa-encoded genes, Q10, directs the hepatic synthesis of a nonmembrane bound molecule that is secreted in association with f32-microglobulin and accumulates in the serum (7)(8)(9)(10)(11)(12).…”