Ganglioside GM2 activator (GM2A) is as a novel pro-survival p53 target in hepatocellular carcinoma

Essential for numerous cell functions sphingolipids occur in a variety of eukaryotic and prokaryotic organisms as well as in viruses as structural components of membranes and lipoproteins. The diverse functions of sphingolipids exceed those of simple building blocks as they bind to cell surfaces and extracellular proteins and are involved in intra- and extracellular signaling. The catabolism of membrane bound complex sphingolipids depends on non-enzymatic co-factors, so-called sphingolipid activator proteins (SAP). The enzyme β-hexosaminidase A (HexA) degrades GM2 gangliosides supported by the GM2-activator protein (GM2A).

p53 serves as a major barrier against malignant transformation and progression by mediating antiproliferative cellular outcomes in response to different types of cellular stress. Metabolic alterations either as an inducer or as a part of the p53-mediated cell response have gained attention over the last decade. However, a p53-dependent regulation of factors involved in ganglioside catabolism and the functional implications are (to the best of our knowledge) largely unknown.

Based on a recently published proteomic dataset¹ we identified GM2A protein being strongly (7-fold) induced upon p53 activation by Nutlin treatment. We could confirm this finding by immunoblotting in Sk-Hep1, HepG2 and HuH6 cells. Furthermore, qRT-PCR analysis and chromatin immunoprecipitation (ChIP) experiments revealed that p53 binds to the GM2A promoter and regulates GM2A transcription. Moreover, depletion of GM2A by two different siRNAs led to reduced cell viability in HuH6 and HepG2 cells, particularly under stressed condtions (Camptothecin treatment). This decrease in cell viability was paralleled by increased PARP-cleavage and rising Caspase-3 levels as indicators of augmented apoptotic cell death.

We conclude that GM2A is a novel transcriptional p53-target with a pro-survival/anti-apoptotic function within the p53 response in HCC.

Comprehensive proteomic, transcriptomic, and lipidomic analyses are currently being conducted to gain detailed insight in the underlying molecular mechanism of the observed phenotype.

Literaturangabe:

1. Holzer K, Drucker E, Roessler S, Dauch D, Heinzmann F, Waldburger N, Eiteneuer EM, Herpel E, Breuhahn K, Zender L, Schirmacher P, Ori A, Singer S. Proteomic Analysis Reveals GMP Synthetase as p53 Repression Target in Liver Cancer. AM J Pathol. 2017 Feb;187(2):228 – 235.