RETRACTED: Increased Ras GTPase activity is regulated by miRNAs that can be attenuated by CDF treatment in pancreatic cancer cells

Abstract

This article has been retracted: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy). This article has been retracted at the request of the Editor in Chief. An investigation by Wayne State University identified a discrepancy between the data reported in Figures 1 A and 3 and the original collected data. The investigation committee concluded that this undermined the scientific basis of the publication, that no credible replacement data were available, and advised that the publication should be retracted.

Figure 1

Ras GTPase activity and basal levels of K-Ras expression in human pancreatic cancer (PC) cell lines COLO-357, BxPC-3 and MIAPaCa-2 cells. Ras expression and its GTPase activity were significantly higher in MIAPaCa-2 cells followed by COLO-357 and BxPC-3 (A). Relative expressions of let-7a, let-7b, let-7c, let-7d, let-7e, let-7f, let-7i (B), miR-21 and miR-143 (C) as assessed by qRT-PCR in COLO-357, BxPC-3 and MIAPaCa-2 cells. P values represent comparison between BxPC-3 and MIAPaCa-2 cells as calculated by the paired t test.

Figure 2

Comparative level of expression of let-7a, let-7e, let-7f, let-7i, and miR-143 in untreated and treated cells with CDF (0.5– 1 μM) for 48h in COLO-357 (A), BxPC-3 (B) and MIAPaCa-2 cells (C). There was a significant up-regulation of let-7i, and miR-143 expression with CDF treatment. P values represent comparison between untreated and CDF 1 μM treated cells as calculated by the paired t test.

Figure 3

Ras GTPase activity and the levels of K-Ras expression in human PC cell lines after miR-21 anti-sense transfection; COLO-357 (A), BxPC-3 (B) and MIAPaCa-2 cells (C) by western blot analysis. A significant inhibition of Ras GTPase activity and its expression was observed in MIAPaCa-2 and COLO-357 cells transfected with anti-sense miR-21. No such effect was observed in control miRNA transfected cells.

Figure 4

CDF exhibited anti-tumor activity in MIAPaCa-2 pancreatospheres induced tumors in a xenograft mouse model (A), which was consistent with inhibition of Ras expression and its GTPase activity (B), and re-expression of let-7 family (C) and miR-143 expression (D) in tumor remnants. The arrow indicates starting day of the treatment. P values were calculated by the paired t test.

Figure 5

Re-expression of miR-143 by pre-miR-143 precursor or CDF treatment in COLO-357 cells showed increased expression of miR-143 as assessed by qRT-PCR (A), and corresponding decrease expression of Ras and its GTPase activity as assessed by western blot (B) compared to control cells. The above treatment also led to reduced cell viability as assessed by MTT assay (C) and clonogenicity as assessed by colony formation assay (D).

Figure 6

Re-expression of let-7i by pre-let-7i precursor transfection or treatment of MIAPaCa-2 cells by CDF led to increased expression of let-7i as assessed by qRT-PCR (A), and showed decreased levels of Ras expression and its GTPase activity (B) compared to control cells. The above treatment also led to reduced cell viability as assessed by MTT assay (C) and clonogenicity as determined by colony formation assay (D).

Figure 7

Over-expression of let-7i using stably transfected pre-let-7i in MIAPaCa-2 cells in vivo showed decreased tumor growth rate in a subcutaneous tumor xenograft model (A), consistent with increased levels of let-7i expression (B), which was associated with decreased levels of Ras expression and its activity (C) compared to control vector MIAPaCa-2 cells. n=5 mice for each group.