miR-19b represses endogenous p53 and its downstream components. (A) Western blot of p53, p21, and Bax protein in different cells. Due to overexpression of miR-19b, generation of endogenous p53 and its downstream proteins were significantly inhibited in all three cell types, while miR-19a did not alter the expression level of any proteins. Corresponding protein levels were quantified and shown at right. (B) The mRNA level of p53 in Hela, MCF7, and Huh7 cells transfected with miR-19b or negative control (NC) as examined by qRT-PCR. No significant difference was observed between the two groups in all cell types. (C) The expression level of miR-19a and miR-19b examined by qRT-PCR in Hela and MCF7 cells transfected with miR-19b, miR-19b sponge (19bs), and p53 cDNA together with miR-19b and miR-NC. (D) Western blot of p53, p21, and Bax in cells described in C. p53 protein level was decreased by overexpression of miR-19b, but increased when miR-19b was blocked by the sponge. The level of p21 and Bax changed along with p53. Corresponding protein levels were quantified and shown at right. Data in A and B are tested by a Mann-Whitney test, and in C and D are tested by an ANOVA test and further verified by a Bonferroni post-test. All histograms are presented as mean values ± SEM derived from five independent experiments.