Publications

Although pulmonary hypertension is a well-described manifestation of systemic lupus erythematosus, there are few data regarding the pulmonary artery pressure response to exercise. We hypothesized that exercise capacity was reduced and that the pulmonary artery pressure response to exercise was abnormal in patients with systemic lupus erythematosus. To test these hypotheses, we performed Doppler exercise echocardiography in 18 patients with lupus and 10 normal control subjects. Exercise duration was significantly reduced in the patients with lupus (8.1 vs 14.4 minutes for control subjects, p < or = 0.001). Pulmonary artery pressure was significantly higher in the patients with lupus at rest and during the first two stages of exercise (p < 0.05). Cardiac indexes at rest were similar in the two groups, suggesting that increased pulmonary vascular resistance was the mechanism for the higher pulmonary pressure we observed. We conclude that abnormal exercise hemodynamics may contribute to reduced exercise capacity in patients with lupus.

The cytokine interleukin 1 alpha (IL-1 alpha) is a critical mediator of the immune and inflammatory responses. A unique determinant of its activity as compared with IL-1 beta may be its association with the plasma membrane. While the biologic activity of "membrane IL-1" has been extensively reported, the mechanism of membrane binding remains unclear. We report that the N terminus of the 31-kDa IL-1 alpha precursor is myristoylated on specific internal lysine residues. Immunoprecipitation of [3H]myristic acid-radiolabeled human monocyte lysates with IgG antibodies to the 31-kDa IL-1 alpha precursor recovered a protein with the physicochemical properties of the IL-1 alpha N-terminal propiece (16 kDa, pI 4.45). Glycyl N-myristoylation of this protein is precluded by the absence of a glycine residue at position 2, suggesting that the propiece is myristoylated on epsilon-amino groups of lysine. To determine which lysine(s) are acylated, a series of synthetic peptides containing all lysines found in the IL-1 alpha N-terminal propiece were used in an in vitro myristoylation assay containing peptide, myristoyl-CoA, and monocyte lysate as enzyme source. Analysis of the reaction products by reverse-phase HPLC and gas-phase sequencing demonstrated the specific myristoylation of Lys-82 and Lys-83, yielding predominantly monoacylated product. A conserved sequence in the IL-1 beta propiece was myristoylated with at least 8-fold less efficiency. Acylation of the IL-1 alpha precursor by a previously unrecognized lysyl epsilon-amino N-myristoyl-transferase activity may facilitate its specific membrane targeting.

Agonists for Gi-coupled receptors augment Gs-stimulated cAMP synthesis in human embryonic kidney (HEK) 293 cells transiently expressing the type II isozyme of adenylylcyclase (AC-II). This augmentation, mediated by beta gamma subunits released from activated Gi, can be blocked by expression of the alpha subunit (alpha t) of retinal transducin (Gt), which presumably sequesters free beta gamma (Federman, A. D., Conklin, B. R., Schrader, K. A., Reed, R. R., and Bourne, H. R. (1992) Nature 356, 159-161). The alpha subunit of Gq, representing a G protein family distinct from both Gs and Gi, mimicked the inhibitory effect of alpha t, suggesting that hormonal stimulation of endogenous Gq might also release beta gamma subunits and thereby augment AC-II activity. Agonists for either of two Gq-coupled receptors did augment Gs-stimulated cAMP synthesis in HEK-293 cells expressing AC-II, but this effect was not blocked by expression of alpha t. The increased stimulation of AC-II was probably not mediated by the release of beta gamma subunits from Gq but rather by activation of protein kinase C (PKC) because of the following. (a) Phorbol esters, which activate PKC directly, elevated cAMP 2-fold in HEK-293 cells transfected with AC-II; this increase was synergistic with Gs-mediated activation of AC-II. (b) Treatments that partially inhibit or down-regulate PKC also partially prevented stimulation of AC-II by phorbol esters or by agonists for Gq-coupled receptors. Taken together, these results indicate that AC-II can integrate regulatory signals transmitted by at least three classes of G proteins; extracellular signals acting through Gs are enhanced synergistically by simultaneous signals transduced by Gi or Gq and mediated via beta gamma or PKC, respectively.