The Inhibitor of Growth 1 (ING1) Is Involved in Trichostatin A-Induced Apoptosis and Caspase 3 Signaling in p53-Deficient Glioblastoma Cells

Abstract

Prognosis for patients with glioblastoma multiforme (GBM) is poor. Inhibitors of histone deacetylases (HDACi) like trichostatin A (TSA) are promising alternatives to conventional treatment. Deficient tumor suppressor functions, such as TP53 mutations and p14(ARF)/p16(INK4a) deletions, are characteristic for GBM and can cause resistance to DNA damaging agents such as cisplatin and to HDACi like TSA. The type II tumor suppressor Inhibitor of growth 1 (ING1) is involved in DNA damage response and histone modification. We have previously shown that ING1 is downregulated in GBM and involved in glioma-induced angiogenesis and in cisplatin-induced apoptosis in malignant glioma cells. Hence, the goal of our present study was to investigate whether TSA affects ING1 protein expression and also whether modulating ING1 levels affects TSA-induced apoptosis in malignant glioma cells that contain deficient p53 function and inactive pl4(ARF)/p16(INK4a) signaling. If so, we asked, which apoptotic pathway might be the major mediator beyond this interaction. To test whether ING1 proteins function in TSA-induced apoptosis in GBM, we analyzed TSA effects in LN229 GBM cells, which harbor TP53 mutations and INK4a deletion, following ING1 knockdown by siRNA. Expression of ING1, acetylated core histones H3 and H4, and the proapoptotic proteins caspase 3 and Fas-associated death domain (FADD) was determined by Western blotting. Percentages of apoptotic cells were obtained by flow cytometry. TSA induced the major ING1 isoform p33(ING1b) and increased levels of both histone acetylation and apoptosis in LN229 cells. ING1 knockdown cells revealed marked resistance to TSA-induced apoptosis, impairment of caspase 3 activation, and suppression of FADD. The data suggest that ING1 contributes to TSA-induced apoptosis in GBM cells with deficient p53 and p14(ARF)/p16(INK4a) functions, possibly by regulating FADD/caspase 3 signaling.

Src Regulates the Activity of the ING1 Tumor Suppressor

“…In this study we have shown that ING1 physically associates with, and is a target substrate of the Src tyrosine kinase in vitro and in vivo , that Src contributes to reducing levels of ING1 by phosphorylation-dependent and phosphorylation-independent mechanisms, and that such reduction blocks the ability of ING1 to induce apoptosis. This suggests that Src may contribute to regulating ING1 levels and thus act to alter cell susceptibility to undergoing apoptosis since ING1 has been reported by many groups to enhance apoptosis [9]–[11], [41]–[47].…”

ING4 Inhibits Proliferation and Induces Apoptosis in Human Melanoma A375 Cells via the Fas/Caspase-8 Apoptosis Pathway

“…ING1 may contribute to trichostatin A-induced apoptosis in p53-deficient glioblastoma cells by regulating the Fas/caspase-3 apoptosis pathway [5]. Furthermore, ING3-mediated UV-induced apoptosis via the Fas/caspase-8 pathway was reported in human melanoma cells [6].…”

ING1 induces apoptosis through direct effects at the mitochondria

“…25, 26, 27, 28, 29, 30, 31 Ectopic expression of ING1 also induces apoptosis, 19 and although initial reports suggested this role may be p53-dependent, 20, 32, 33 more recent evidence suggest that the ING family also has effects on apoptosis that are independent of p53. 34, 35, 36, 37 ING1 interacts with proliferating cell nuclear antigen (PCNA) via the PCNA-interacting protein (PIP) domain in a stress-induced manner. 13 The PIP domain is necessary for the ability of ING1 to maximally induce apoptosis upon overexpression and in response to DNA damage.…”