Shank-interacting protein–like 1 promotes tumorigenesis via PTEN inhibition in human tumor cells
Lizhi He, … , Adrian P. Rybak, Damu Tang
Lizhi He, … , Adrian P. Rybak, Damu Tang
Published May 10, 2010
Citation Information: J Clin Invest. 2010;120(6):2094-2108. https://doi.org/10.1172/JCI40778.
View: Text | PDF
Research Article Oncology

Shank-interacting protein–like 1 promotes tumorigenesis via PTEN inhibition in human tumor cells

Abstract

Inactivation of phosphatase and tensin homolog (PTEN) is a critical step during tumorigenesis, and PTEN inactivation by genetic and epigenetic means has been well studied. There is also evidence suggesting that PTEN negative regulators (PTEN-NRs) have a role in PTEN inactivation during tumorigenesis, but their identity has remained elusive. Here we have identified shank-interacting protein–like 1 (SIPL1) as a PTEN-NR in human tumor cell lines and human primary cervical cancer cells. Ectopic SIPL1 expression protected human U87 glioma cells from PTEN-mediated growth inhibition and promoted the formation of HeLa cell–derived xenograft tumors in immunocompromised mice. Conversely, siRNA-mediated knockdown of SIPL1 expression inhibited the growth of both HeLa cells and DU145 human prostate carcinoma cells in vitro and in vivo in a xenograft tumor model. These inhibitions were reversed by concomitant knockdown of PTEN, demonstrating that SIPL1 affects tumorigenesis via inhibition of PTEN function. Mechanistically, SIPL1 was found to interact with PTEN through its ubiquitin-like domain (UBL), inhibiting the phosphatidylinositol 3,4,5-trisphosphate (PIP3) phosphatase activity of PTEN. Furthermore, SIPL1 expression correlated with loss of PTEN function in PTEN-positive human primary cervical cancer tissue. Taken together, these observations indicate that SIPL1 is a PTEN-NR and that it facilitates tumorigenesis, at least in part, through its PTEN inhibitory function.

Authors

Lizhi He, Alistair Ingram, Adrian P. Rybak, Damu Tang

×

Figure 1

SIPL1 reduces PTEN function.

Options: View larger image (or click on image) Download as PowerPoint
SIPL1 reduces PTEN function. (A) U87 cells were infected with retrovirus...
(A) U87 cells were infected with retrovirus expressing EV, SIPL1, PTEN, PTEN-IRES-GFP, and PTEN-IRES-SIPL1. Expression of the respective proteins was demonstrated (Supplemental Figure 2A). Infected cells were cultured in hygromycin-containing medium for 2–3 weeks until surviving colonies formed, which were stained with crystal violet (Supplemental Figure 2A). Numbers of surviving cell colonies were quantified using ImageJ software and standardized as percentages of surviving EV cells. “Mock” indicates uninfected U87 cells were cultured in hygromycin-containing medium. Experiments were repeated twice. (B) U87 cells were infected with the indicated retrovirus. Cells (2 × 104) were then seeded in a 6-well soft agar plate and cultured for 4 weeks. Cell colonies were quantified. Experiments were repeated twice. (C) DU145, (D) HeLa, and (E) HCC1954 cells were infected with retrovirus expressing a control (Ctrl) siRNA or SIPL1 siRNA, PTEN siRNA, or SIPL1/PTEN siRNA. Knockdown of individual proteins was demonstrated (see Figure 2A). Infected cells were selected in puromycin. Surviving cell colonies were stained (see Supplemental Figure 3A for typical images), and the number of surviving colonies was graphed. Experiments were repeated 3 times.