Publications

Complementary DNAs corresponding to the human receptor for interleukin 2 (IL-2) have been molecularly cloned, sequenced, and expressed in COS-1 cells. The human genome appears to contain a single structural gene for this receptor; however, when transcribed at least two messenger RNAs (mRNAs) are produced which vary in length due to the use of different polyadenylation signals. Sequence analysis of the cloned complementary DNAs indicates an alternate pathway of mRNA processing for this receptor. Splicing of a 216 base pairs segment contained within the protein coding region results in an mRNA unable to code for the IL-2 receptor. In contact complementary DNAs corresponding to unspliced mRNA encode membrane receptors which bind both IL-2 and anti-Tac (monoclonal anti-IL-2 receptor antibody). Analysis of the deduced amino acid sequence reveals that the receptor is composed of 272 amino acids including a signal peptide 21 amino acids in length. Hydrophobicity analysis suggests a single 19 amino acid transmembrane domain. A short intracytoplasmic domain composed of 13 amino acids is present at the carboxy terminus and contains three potential phosphate acceptor sites (serine and threonine but not tyrosine) and typical positively charged amino acids presumably involved in cytoplasmic anchoring. Two sites for N-linked glycosylation sites and numerous extracytoplasmic O-linked glycosylation sites are present.

We have used cDNAs for the human interleukin 2 (IL-2) receptor to study IL-2 receptor gene expression in normal activated T cells. Resting T cells do not contain detectable IL-2 receptor mRNA. Within 1 hr after stimulation with phytohemagglutinin (PHA), a large, presumably nuclear precursor RNA species is seen, which then gradually disappears. Mature IL-2 receptor mRNA forms appear within 8 hr after stimulation, reach peak levels between 8 and 24 hr, and then decline. Thus, in PHA-activated lymphocytes the rise and fall in IL-2 receptor mRNA levels precede by more than 24 hr the peak and decline of IL-2 receptor protein expression occurring at the cell surface. 4 beta-Phorbol 12-myristate 13-acetate (PMA) also stimulates IL-2 receptor mRNA and protein expression by T cells. Combinations of optimal concentrations of PHA and PMA produce an additive effect on IL-2 receptor mRNA levels, suggesting that PHA and PMA may induce IL-2 receptor gene expression through different, complementary mechanisms. Nuclease S1-protection assays indicate that IL-2 receptor mRNAs may differ in length due to the use of three different polyadenylylation signals. Further, these assays demonstrate the presence of transcripts that lack a 216-base segment within the protein-coding region and thus do not encode a functional IL-2 receptor. Nuclear transcription assays indicate that the increase in IL-2 receptor mRNA is reflected at the level of transcription. Thus, IL-2 receptor gene regulation controls IL-2 receptor expression at the cell surface and is intimately linked to the control of T-cell proliferation.

Interleukin-2 (IL-2) is a lymphokine synthesized by some T-cells following activation. Resting T-cells do not express IL-2 receptors, but receptors are rapidly expressed on T-cells following interaction of antigens, mitogens, or monoclonal antibodies with the antigen-specific T-cell receptor complex. Using anti-Tac, a monoclonal antibody that recognizes the IL-2 receptor, the receptor has been purified and shown to be a Mr 33,000 peptide that is posttranslationally glycosylated to a Mr 55,000 mature form. Normal resting T-cells and most leukemic T-cell populations do not express IL-2 receptors; however, the leukemic cells of the 11 patients examined who had human T-cell lymphotropic virus-associated adult T-cell leukemia expressed the Tac antigen. In human T-cell lymphotropic virus-I infected cells, the Mr 42,000 long open reading frame protein encoded in part by the pX region of this virus may act as a transacting transcriptional activator that induces IL-2 receptor gene transcription, thus providing an explanation for the constant association of IL-2 receptor expression with adult T-cell lymphotropic virus-I infection of lymphoid cells. The constant expression of large numbers of IL-2 receptors which may be aberrant may play a role in the uncontrolled growth of adult T-cell leukemia cells. Two patients with Tac-positive adult T-cell leukemia have been treated with the anti-Tac. One of the patients had 6- and 3-mo remissions of his leukemia following two courses of therapy with this monoclonal antibody directed toward this growth factor receptor.

Because hypoxia has been shown to cause bronchoconstriction and to potentiate bronchomotor responsiveness in animals, we investigated whether hypoxia has similar effects in subjects with asthma. We measured specific airway resistance (SRaw; the mean of 5 sequential readings taken 30 s apart) before and immediately after each of 15 asthmatic subjects breathed a mixture of 8% O2 in N2 until hemoglobin saturation (SaO2; by ear oximetry) fell to 80% or less for at least 2 min. We maintained end-tidal CO2 at resting levels, the temperature of the inspirate at 22.0 +/- 1.1 degrees C, and the dew point at 18.5 +/- 1.6 degrees C (mean +/- SD). The SaO2 fell to 70 +/- 8%; minute ventilation rose to 28.4 +/- 8.5 L/min, and heart rate rose by 27 +/- 6 beats/min. The SRaw did not increase significantly in the group (baseline SRaw, 6.61 +/- 2.36; posthypoxia SRaw, 6.69 +/- 2.21 L X cm H2O/L/s) or in any subject. To determine if hypoxia increases bronchomotor responsiveness, we also compared the responses to eucapnic hyperpnea with dry air and with dry gas mixtures of 7 to 10% O2 in N2 in a randomized, double-blind sequence in 9 of the subjects. We measured SRaw in each subject before and after stepwise increases in minute ventilation, for 3 min at each level, until SRaw doubled or until the subject's maximal voluntary ventilation was achieved. The SaO2 fell to 82% or less at each level of ventilation with the hypoxic gas mixture. The 2 stimulus-response curves thus obtained did not differ in any subject.(ABSTRACT TRUNCATED AT 250 WORDS)