2), which corresponds to the highest change in expression level and lowest risk for false positives. of sortilin were significantly reduced by CADA, although to a lesser extent as compared with human CD4. Our data demonstrate that a small signal peptide-binding drug is able to down-modulate the expression of human CD4 and sortilin, apparently with low impact on the cellular proteome. According to the World Health Organization, the human immunodeficiency virus (HIV) has infected almost 78 million people worldwide since its discovery in the early eighties, resulting in the KIAA0243 death of more than 34 Cefepime Dihydrochloride Monohydrate million people. Currently, 25 different Food and Drug Administration-approved anti-HIV drugs are in clinical use, turning HIV and acquired immune deficiency syndrome into a more chronic disease, yet not curable. In addition , HIV can develop resistance to almost all classes of antiretroviral drugs, making the development of new therapies and anti-HIV drugs an ongoing challenge (1). The synthetic small molecule cyclotriazadisulfonamide (CADA; 1Fig. 1A) was identified as a novel anti-HIV agent in an earlier screening program (2). This compound prevents viral entry of different HIV-1 lab strains and clinical isolates into T lymphocytes but does not interact with viral components. Instead, CADA down-modulates the cell surface expression of the human CD4 (hCD4) glycoprotein (27), known as the main receptor for HIV entry (8). Moreover, a strict correlation between the hCD4 down-modulating activity and anti-HIV potency of CADA-derived compounds has been demonstrated (3). == Fig. 1 . == Cefepime Dihydrochloride Monohydrate CADA dose-dependently down-modulates surface hCD4 expression. (A) Structure of cyclotriazadisulfonamide (CADA). (B) Flow cytometric determination of the hCD4 surface expression on SUP-T1 cells after 72 h treatment with 16 mCADA, to verify hCD4 down-modulation by CADA in the samples subjected to PowerBlotTManalysis. Dotted line: unstained control; black: untreated control; Cefepime Dihydrochloride Monohydrate gray: CADA. (C) After 72 h treatment of SUP-T1 cells with CADA, hCD4 was detected with Western blotting under nonreducing conditions. One representative blot out of four is shown. (D) Flow cytometric analysis of the hCD4 surface expression level before lysis (left axis, solid line, mean S. E., n= 5, absolute IC50= 0. 63 m). Total hCD4 protein levels from the immunoblots in (C) were quantified and normalized to the clathrin control (right axis, dotted line, mean S. E., n= 4, absolute IC50= 0. 71 m). Absolute IC50: CADA concentration that reduces the hCD4 expression to 50% of the untreated control. Recently, the mechanism of action of CADA has been unraveled: The drug selectively binds to the signal peptide (SP) of the hCD4 preprotein and prevents it from being translocated into the lumen of the endoplasmic reticulum (ER) (9). Signal peptides (also called signal sequences) are located at the amino terminus of preproteins destined for secretion or plasma membrane insertion. They are crucial for targeting those proteins to the secretory pathway (10). Despite their distinct functional role, signal peptides are diverse and lack a conserved primary sequence (11). Our previous studies showed that hCD4 protein biogenesis is inhibited by CADA in a signal-peptide-dependent way, resulting in a significant down-modulation of cell surface hCD4 levels. They also suggested selectivity of CADA for hCD4 as the compound does not affect cell surface expression of 14 different T lymphocyte receptors nor CD4 from nonprimate species. In addition , cell lysate analysis with concanavalin A agarose beads demonstrated no changes in the expression of glycosylated membrane proteins other than hCD4 (2, 9). Cefepime Dihydrochloride Monohydrate Here, we employed a PowerBlotTMWestern Array to identify potential other substrates of CADA (besides hCD4) in human CD4+T lymphocytes. This high-throughput immunoblotting technology simultaneously evaluates changes in the expression and posttranslational modification of several hundreds of cellular signaling proteins in total cell extracts from treated and untreated cells. Analysis identified a small subset of the 444 detected proteins as being affected by CADA. Of these, the signal-peptide-containing membrane protein sortilin was validated as a new substrate of CADA. == MATERIALS AND METHODS == == == == == == Compounds and Antibodies == Cefepime Dihydrochloride Monohydrate Cyclotriazadisulfonamide hydrochloride was dissolved in dimethyl sulfoxide.
2), which corresponds to the highest change in expression level and lowest risk for false positives
