High-mobility group A1 inhibits p53 by cytoplasmic relocalization of its proapoptotic activator HIPK2
Giovanna Maria Pierantoni, … , Silvia Soddu, Alfredo Fusco
Giovanna Maria Pierantoni, … , Silvia Soddu, Alfredo Fusco
Published March 1, 2007
Citation Information: J Clin Invest. 2007;117(3):693-702. https://doi.org/10.1172/JCI29852.
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Research Article Oncology

High-mobility group A1 inhibits p53 by cytoplasmic relocalization of its proapoptotic activator HIPK2

Abstract

High-mobility group A1 (HMGA1) overexpression and gene rearrangement are frequent events in human cancer, but the molecular basis of HMGA1 oncogenic activity remains unclear. Here we describe a mechanism through which HMGA1 inhibits p53-mediated apoptosis by counteracting the p53 proapoptotic activator homeodomain-interacting protein kinase 2 (HIPK2). We found that HMGA1 overexpression promoted HIPK2 relocalization in the cytoplasm and inhibition of p53 apoptotic function, while HIPK2 overexpression reestablished HIPK2 nuclear localization and sensitivity to apoptosis. HIPK2 depletion by RNA interference suppressed the antiapoptotic effect of HMGA1, which indicates that HIPK2 is the target required for HMGA1 to repress the apoptotic activity of p53. Consistent with this process, a strong correlation among HMGA1 overexpression, HIPK2 cytoplasmic localization, and low spontaneous apoptosis index (comparable to that observed in mutant p53–carrying tumors) was observed in WT p53–expressing human breast carcinomas. Hence, cytoplasmic relocalization of HIPK2 induced by HMGA1 overexpression is a mechanism of inactivation of p53 apoptotic function that we believe to be novel.

Authors

Giovanna Maria Pierantoni, Cinzia Rinaldo, Marcella Mottolese, Anna Di Benedetto, Francesco Esposito, Silvia Soddu, Alfredo Fusco

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Figure 5

HMGA1 inhibits p53-induced apoptosis by interfering with HIPK2 nuclear localization.

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HMGA1 inhibits p53-induced apoptosis by interfering with HIPK2 nuclear l...
(A) For coimmunoprecipitation of exogenous proteins, H1299 cells were transfected as indicated and TCEs were immunoprecipitated with anti-HA Ab. Immunocomplexes were analyzed by Western blot (WB) as indicated. For coimmunoprecipitation of endogenous proteins, TCEs from H1299 cells were immunoprecipitated with anti-HMGA1 or anti-IgG as negative control and analyzed by Western blot. (B) H1299 cells were transfected with increasing doses of pCEFL-Hmga1. HA-HMGA1 expression was analyzed by immunofluorescence with anti-HA and tetramethylrhodamine isothiocyanate–conjugated Abs. Nuclei were stained with Hoechst. Images are from 1 representative experiment of the 3 performed. (C) H1299 cells were transfected and immunostained as in B; the percentage of HMGA1-positive cells with cytoplasmic staining was counted. (D) EGFP-HIPK2 subcellular localization in H1299 cells transfected with the indicated vectors. EGFP-HIPK2 is visible by its intrinsic green fluorescence. HA-HMGA1 expression was analyzed as in B. (E) H1299 cells were transfected with pCEFL-Hmga1 and pEGFP-HIPK2 expression vectors at the indicated molar ratios. EGFP-HIPK2 and HA-HMGA1 expression and their subcellular localization were analyzed by immunofluorescence as in D. (F) H1299 cells were transfected and immunostained as in E. The percentages of HMGA1-positive cells with nuclear or cytoplasmic staining of EGFP-HIPK2 were counted. Cells with a pCEFL-Hmga1 dose of 0 were cotransfected with pCEFL empty vector.