Expression and Regulation of Prostate Apoptosis Response-4 (Par-4) in Human Glioma Stem Cells in Drug-Induced Apoptosis

Abstract

Gliomas are the most common and aggressive of brain tumors in adults. Cancer stem cells (CSC) contribute to chemoresistance in many solid tumors including gliomas. The function of prostate apoptosis response-4 (Par-4) as a pro-apoptotic protein is well documented in many cancers; however, its role in CSC remains obscure. In this study, we aimed to explore the role of Par-4 in drug-induced cytotoxicity using human glioma stem cell line - HNGC-2 and primary culture (G1) derived from high grade glioma. We show that among the panel of drugs- lomustine, carmustine, UCN-01, oxaliplatin, temozolomide and tamoxifen (TAM) screened, only TAM induced cell death and up-regulated Par-4 levels significantly. TAM-induced apoptosis was confirmed by PARP cleavage, Annexin V and propidium iodide staining and caspase-3 activity. Knock down of Par-4 by siRNA inhibited cell death by TAM, suggesting the role of Par-4 in induction of apoptosis. We also demonstrate that the mechanism involves break down of mitochondrial membrane potential, down regulation of Bcl-2 and reduced activation of Akt and ERK 42/44. Secretory Par-4 and GRP-78 were significantly expressed in HNGC-2 cells on exposure to TAM and specific antibodies to these molecules inhibited cell death suggesting that extrinsic Par-4 is important in TAM-induced apoptosis. Interestingly, TAM decreased the expression of neural stem cell markers - Nestin, Bmi1, Vimentin, Sox2, and Musashi in HNGC-2 cell line and G1 cells implicating its potential as a stemness inhibiting drug. Based on these data and our findings that enhanced levels of Par-4 sensitize the resistant glioma stem cells to drug-induced apoptosis, we propose that Par-4 may be explored for evaluating anti-tumor agents in CSC.

The tumor suppressor prostate apoptosis response-4 (Par-4) is regulated by mutant IDH1 and kills glioma stem cells

“…Very little work on Par-4 in gliomas has been done; so far all of it has been strictly in vitro using cell lines and/or high-passage patient-derived tumor cells grown in serum (29, 53, 59). In those studies, Par-4 mediated some of the toxic activity of temozolomide (29, 59), and forced overexpression of full-length Par-4 was sufficient to kill glioma cell lines (53).…”

“…In those studies, Par-4 mediated some of the toxic activity of temozolomide (29, 59), and forced overexpression of full-length Par-4 was sufficient to kill glioma cell lines (53). Very little is known about whether any key driver mutations in gliomas can affect Par-4, the prognostic significance of Par-4, or whether its SAC domain can kill GSCs.…”

“…Induced expression of full-length Par-4 kills many glioma cell lines (53). It is also critical for the apoptotic response to chemotherapy, both in human GBM cell lines (59) and in GSCs that have been passaged many times in serum (29). Yet its full impact in gliomas remains unknown, including whether it is regulated by any driver mutations, its activity against patient-derived GSCs in vivo , and its significance as a prognostic marker.…”

Simultaneous dual targeting of Par-4 and G6PD: a promising new approach in cancer therapy? Quintessence of a literature review on survival requirements of tumor cells

“…This success was seen only in combination of the two substances while monotherapy either with Tamoxifen or with Par-4 alone failed [57]. …”

Papel da expressão celular e extracelular do Par-4 na formação tumoral e sensibilidade a droga

“…Sendo assim, diversos estímulos são encontrados na literatura descritos como moduladores da expressão de Par-4, dentre eles: fatores de crescimento e hormonal (CASOLARI et al, 2011;CHAN et al, 1999;CHUNG et al, 2007); quimioterápicos (JAGTAP et al, 2014); diversas quinases (DE THONEL et al, 2014;GURUMURTHY;VASUDEVAN, 2005); membros da família RAS (DONNINGER et al, 2010);p53 (BURIKHANOV et al, 2014);Fbxo45 (CHEN et al, 2014); e miRNAs (DU et al, 2015). …”