Effects of ATRA and IFNs on the expression of Stat, p48, Jak 1, Jak 2, and Tyk 2 proteins in NB4 and HeLa cells. NB4 (4 ×10⁵/mL) or HeLa (a confluent 25 cm2 flask) cells were treated for 4 days with medium alone (Medium) and medium containing ATRA (10⁻⁶ mol/L), IFNα (1,000 U/mL), and IFNγ (1,000 U/mL) as indicated. Cells were harvested, lysed, and subjected to Western blot analysis, using antibodies specific for Stat 1α, Stat 2, Stat 3, and Stat 4 (A), p48 (B), Jak1, Jak 2, and Tyk 2 (C). For Stat 3 and Jak 1, 100 μg of protein/lane were used, whereas for all the other samples, 10 mg of protein/lane were used. In (B), the apparent molecular weight of standard proteins (carbonic anhydrase [28 kD], ovalbumin [43 kD], bovine serum albumin [69 kD], and phosphorylase B [105 kD]) is indicated on the right. The apparent molecular weight of Stat proteins, Jak 1, Jak 2, and Tyk 2 is indicated on the right of (A) and (C). Western blots representative of at least two independent experiments are shown.