PBA Preferentially Impairs Cell Survival of Glioblastomas Carrying mutp53 by Reducing Its Expression Level, Stabilizing wtp53, Downregulating the Mevalonate Kinase and Dysregulating UPR.

Maria Anele Romeo,Alessia Garufi,Maria Saveria Gilardini Montani,Gabriella D’Orazi,Rossella Benedetti,Mara Cirone

doi:10.3390/biom10040586

Abstract

Phenylbutyrate (PBA) is a derivative of Butyric Acid (BA), which has the characteristics of being a histone deacetylase (HDAC) inhibitor and acting as a chemical chaperone. It has the potential to counteract a variety of different diseases, from neurodegeneration to cancer. In this study, we investigated the cytotoxic effect of PBA against glioblastoma cells carrying wt or mutant (mut) p53 and found that it exerted a higher cytotoxic effect against the latter in comparison with the former. This could be due to the downregulation of mutp53, to whose pro-survival effects cancer cells become addicted. In correlation with mutp53 reduction and wtp53 activation, PBA downregulated the expression level of mevalonate kinase (MVK), a key kinase of the mevalonate pathway strongly involved in cancer cell survival. Here we differentiated the chaperoning function of PBA from the others anti-cancer potentiality by comparing its effects to those exerted by NaB, another HDACi that derives from BA but, lacking the phenyl group, cannot act as a chemical chaperone. Interestingly, we observed that PBA induced a stronger cytotoxic effect compared to NaB against U373 cells as it skewed the Unfolded Protein Response (UPR) towards cell death induction, upregulating CHOP and downregulating BIP, and was more efficient in downregulating MVK. The findings of this study suggest that PBA represents a promising molecule against glioblastomas, especially those carrying mutp53, and its use, approved by FDA for urea cycle disorders, should be extended to the glioblastoma anticancer therapy.

Highlights

Phenylbutyrate (PBA) is an aromatic short-chain fatty acid known to exert multiple benefic effects, as it holds anti-inflammatory and anti-cancer properties
As evaluated by trypan blue (Figure 1a,c,e) and MTT (Figure 1b,d,f) assays, cell survival was reduced in a dose-dependent fashion in all cell lines, U87 cells were less susceptible to such treatment in comparison to U373 and T98
The latter experiment indicates that PBA triggered an apoptotic cell death in both glioblastoma cell lines, more efficiently in the mutp53-carrying U373 and T98 cells

Summary

Introduction

Phenylbutyrate (PBA) is an aromatic short-chain fatty acid known to exert multiple benefic effects, as it holds anti-inflammatory and anti-cancer properties. ER stress/Unfolded Protein Response (UPR), usually activated in the cancer cells due to the intrinsic or extrinsic insults, may sustain cancer survival/chemoresistance [1] Both PBA and NaB are histone deacetylase inhibitors (HDACis), and as such, they may hold a strong anti-cancer potential [2], at sublethal doses. Gliomas arise from oncogenic transformation of glial cells, more frequently astrocytes, and can behave either as low or as high aggressive cancers The latter include the glioblastoma multiform (GBM), which represents the most common form of gliomas in the adult population. The impact of PBA treatment on mutant and wtp expression, on the mevalonate pathway and ER stress/UPR was addressed as possible mechanisms of cell death induction in U373, T98 and U87, glioblastoma cell lines harboring mutant and wtp, respectively

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