IKA increases CD4 half-life in Nef-expressing cells. (A) Analysis of CD4 stability. Control U937/LN cells or U937/LNefSN (Nef-expressing) cells were pulse-labeled for 45 min with [35S]methionine and [35S]cysteine and chased for 3 h in the absence or presence of IKA. Cell lysates were immunoprecipitated with a normal rabbit serum or a rabbit anti-CD4 antiserum. Lane 1, U937/LN cell lysates immunoprecipitated with normal rabbit serum; lane 2, U937/LN cell lysates (without chase) immunoprecipitated with anti-CD4 antiserum; lane 3, U937/LNefSN cell lysates (with chase) immunoprecipitated with anti-CD4 antiserum; lane 4, U937/LNefSN cell lysates (with chase in the presence of IKA) immunoprecipitated with anti-CD4 antiserum. (B) Western blot analysis of Nef expression. Lane 1, U937/LN cells; lane 2, U937/LNefSN cells; lane 3, U937/LNefSN cells incubated with IKA for 3 h.