High-mobility group A1 inhibits p53 by cytoplasmic relocalization of its proapoptotic activator HIPK2
Giovanna Maria Pierantoni, Cinzia Rinaldo, Marcella Mottolese, Anna Di Benedetto, Francesco Esposito, Silvia Soddu, Alfredo Fusco
Giovanna Maria Pierantoni, Cinzia Rinaldo, Marcella Mottolese, Anna Di Benedetto, Francesco Esposito, Silvia Soddu, Alfredo Fusco
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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 2

HIPK2 rescues the HMGA1 antiapoptotic effect on p53.

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HIPK2 rescues the HMGA1 antiapoptotic effect on p53. (A) H1299 cells wer...
(A) H1299 cells were infected with dl70.3 (– in the p53 row) or Adp53 (+ in the p53 row) viruses at 60 MOI. One hour after infection, cells were transfected with pCEFL-Hmga1 vector or pCEFL control vector and pEGFP-HIPK2 vector or pEGFP empty vector. After 48 hours, floating and adherent cells were collected and analyzed by trypan blue exclusion. Mean ± SD of 3 independent experiments are shown. Expression of the indicated proteins was analyzed by Western blot; the results of 1 indicative experiment of the 3 performed are reported. Expression of γ-tubulin shows equal loading of samples. (B) The same cells reported in A were analyzed by TUNEL assay. One indicative experiment is reported. (C) WT p53–carrying RKO cells overexpressing HA-HMGA1 protein or not, as detected by Western blot (upper panel), were transiently transfected with HIPK2 expression vector as indicated and subjected or not to UV light irradiation (50 J/m2), and the percentage of cell death was measured by trypan blue exclusion 36 hours after irradiation. Expression of the indicated proteins was analyzed by Western blot; shown is 1 indicative experiment of the 3 performed. (D) RKO cells were transiently transfected with HMGA1-specific sense (S) or antisense (AS) oligonucleotides to reduce HMGA1 expression, as detected by Western blot (upper panel). Upon transfection of HIPK2 expression vector, cells were irradiated with UV light and analyzed as in C.