Molecular cloning and characterization of a novel glycoprotein, gp34, that is specifically induced by the human T-cell leukemia virus type I transactivator p40^tax

We have cloned and sequenccd a cDNA encoding gp34, a novel glycoprotein expressed in cells bearing human T-cell leukemia virus type I (HTLV-I). HTLV-I has a transacting transcriptional activator, p40^tax, that is thought to be implicated in leukemogenesis through the activation of cellular enhancers. With a subline (JPX-9) of the human T-cell line Jurkat, in which p40^tax is inducible, gp34 was shown to be of cellular origin and to be transcriptionally activated by p40^tax. It was also demonstrated that two species of mRNA are generated from one copy of the gp34 gene and that these mRNAs encode the identical gp34 product and differ in the 3′ untranslated region. Analysis of the deduced amino acid sequence of gp34 showed that it lacks typical signal peptides; however, it has a hydrophobic stretch for membrane anchoring and four possible N-linked glycosylation sites at the carboxy-terminal portion, indicating that it belongs to the family of membrane proteins whose carboxy-terminal portion protrudes out of the cell. The gp34 gene displayed relatively delayed induction compared with other genes activated by p40^tax. Taken together with the observation of the dependence of gp34 expression on HTLV-I p40^tax, unlike other p40^tax-dependent genes such as those for the interleukin-2 receptor a chain and c-fos, which are expressed or induced under physiological conditions, we predict that the mechanism involved in the induction of gp34 expression by p40^tax is distinct from and more intricate than those for the previously characterized genes.