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Boolean modeling reveals the necessity of transcriptional regulation for bistablity in PC12 Cell Differentiation

ABSTRACT: The nerve growth factor NGF has been shown to cause cell fate decisions towards either differentiation or proliferation depending on the relative activity of downstream pERK, pAKT or pJNK signaling. However, how these protein signals are translated into and fed back from transcriptional activity to complete cellular differentiation over a time span of hours to days is still an open question. Using dynamic proteome and transcriptome data from NGF-stimulated PC12 cells over a time span of 24 hours we inferred a dynamic Boolean model capturing the temporal sequence of protein signaling, transcriptional response and subsequent autocrine feedback. Optimal model topology was achieved by introducing multiple time scales for fast cellular signaling and slower gene response and subsequent fitting to the experimental data. The integrated model confirmed the parallel use of MEK/ERK, AKT/PI3K and JNK/JUN for PC12 cell differentiation. Redundancy of cell signaling is demonstrated from the inhibition of the different MAPK pathways. As suggested in silico and confirmed in vitro, differentiation was substantially suppressed under JNK/JUN inhibition, yet delayed only under MEK/ERK inhibition. Most importantly, we found that sustained transcriptional feedback is necessary to induce bistability in the cell fate switch. De novo Gene expression was necessary to activate autocrine feedback that caused integrin signaling to perpetuate the MAPK activity, finally resulting in the expression of late, differentiation related genes. Thus, the cellular decision towards differentiation depends on the establishment of a transcriptome-induced positive feedback between protein signaling and gene expression thereby constituting a robust control between proliferation and differentiation.

ORGANISM(S): Rattus norvegicus

PROVIDER: GSE74327 | GEO | 2016/03/23

SECONDARY ACCESSION(S): PRJNA299684

REPOSITORIES: GEO

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Project description:The nerve growth factor NGF has been shown to cause cell fate decisions towards either differentiation or proliferation depending on the relative activity of downstream pERK, pAKT or pJNK signaling. However, how these protein signals are translated into and fed back from transcriptional activity to complete cellular differentiation over a time span of hours to days is still an open question. Using dynamic proteome and transcriptome data from NGF-stimulated PC12 cells over a time span of 24 hours we inferred a dynamic Boolean model capturing the temporal sequence of protein signaling, transcriptional response and subsequent autocrine feedback. Optimal model topology was achieved by introducing multiple time scales for fast cellular signaling and slower gene response and subsequent fitting to the experimental data. The integrated model confirmed the parallel use of MEK/ERK, AKT/PI3K and JNK/JUN for PC12 cell differentiation. Redundancy of cell signaling is demonstrated from the inhibition of the different MAPK pathways. As suggested in silico and confirmed in vitro, differentiation was substantially suppressed under JNK/JUN inhibition, yet delayed only under MEK/ERK inhibition. Most importantly, we found that sustained transcriptional feedback is necessary to induce bistability in the cell fate switch. De novo Gene expression was necessary to activate autocrine feedback that caused integrin signaling to perpetuate the MAPK activity, finally resulting in the expression of late, differentiation related genes. Thus, the cellular decision towards differentiation depends on the establishment of a transcriptome-induced positive feedback between protein signaling and gene expression thereby constituting a robust control between proliferation and differentiation. To eludicate the transcriptome response of PC12 cells time-resolved gene expression data of NGF or EGF simulated PC12 were recorded at t = [0.5h 1h, 2h, 3h, 4h, 5h, 6h, 8h, 12h, 24h, 48h] for NGF and at t=[1h, 2h, 3h, 4h, 6h, 8h, 12h, 24h]. Control time points of unstimulated PC12 cells were taken at t=[0h, 2h, 4h, 6h, 8h, 24h, 48h]. Additionally, the MEK-inhibitor UO126 was added together with NGF and the gene response was measured at t=[1h, 2h, 4h, 6h, 8h, 12h, 24h, 48h] and for UO126 alone at t=[1h, 2h, 4h, 8h, 12h, 48h]. Total RNA was isolated, labeled and hybridized to an Illumina ratRef-12 bead array (Illumina, San Diego, CA, USA) according to the manufacturerâ??s protocol.

Project description:Multiple sclerosis (MS) begins as an inflammatory/demyelinating disease but axon injury and neurodegeneration underlie chronic progression. Extracellular matrix (ECM) heparan sulfate proteoglycans (HSPG) are catabolized in acute inflammatory MS lesions and HSPG catabolic products may contribute to failure of neuron repair. Neurite outgrowth and axon elongation of PC12 cells are inhibited when these cells are grown on heparanase-digested HSPG. This inhibition of differentiation is counteracted by nerve growth factor (NGF) but failure to completely reverse inhibition may be due to loss of other growth factors affected by HSPG breakdown. To understand effects of the digested ECM in this model, expression of genes that control differentiation in PC12 cells grown on digested and undigested HSPG will be analyzed. This will permit identification of new potential therapeutic targets for specifically counteracting inhibitory effects of ECM breakdown on neuron regrowth/regeneration in MS. We will compare gene expression patterns of PC12 cells grown on undigested and digested HSPG in the presence and in the absence of NGF over a two week time course to identify the alterations induced by the catabolized HSPG on expression of genes involved in their acquisition of a neuronal phenotype and to determine which genes are and are not targeted by NGF. We are studying ECM HSPG breakdown in human and experimental demyelinating diseases and have developed an in vitro model of ECM catabolism-induced inhibition of neuronal differentiation. Our data indicate that: 1) the numbers of PC12 cells that exhibit neurite outgrowth are decreased when the ECM contains digested, as opposed to intact HSPG; and 2) in the presence of NGF, neurite outgrowth inhibition is counteracted, but complete axonal growth/elongation is not achieved. We will use gene microarray analysis to identify the specific gene expression alterations that digested ECM HSPG induces in PC12 cells in this model of inhibition of neural differentiation. We hypothesize that the genes that are critical for PC12 cell differentiation will be altered by the pathologically altered ECM. Rat pheochromocytoma PC12 cell lines are widely used for analyzing neuronal differentiation. Microarray analyses have identified gene expression patterns associated with their differentiation and response to growth factors. We developed a model of catabolized HSPG inhibition of PC12 cell differentiation that mimics the ECM in MS lesions. HSPG coated on tissue culture dishes is digested with heparanases prior to plating of the PC12 cells. Cells grown on digested ECM without NGF show inhibition of neuronal differentiation (decreased numbers with neurite outgrowth) from days 7 to 14. NGF can partially, but not completely counteract the inhibition, suggesting that signaling pathways in addition to those affected by NGF may be affected by the ECM HSPG digestion. Therefore, we will compare gene expression patterns in samples of cells grown on digested and undigested HSPG ECM both in the presence and absence of NGF. The cells are plated on washed, undigested or digested HSPG-coated 100 mm Petri dishes and grown with or without NGF. Total RNA will be extracted from cells grown in the 4 conditions (w/without digestion; w/without NGF) on 100mm Petri dishes using the RNeasy extraction kit (Qiagen). We propose: 2 duplicate samples/culture condition (8 samples) per time point X 5 time points (days 1, 5, 7, 10, and 14 of culture) = 40 samples/experiment. The RNA will be sent to the Microarray Consortium center for QC check and microarray analysis. Previous analyses of PC12 cells have used the NIA Mouse 15K cDNA clone set scanned with the Agilent Oligo array platform (Vaudry, 2002; Grumolato, 2003). Therefore, this methodology will be useful for comparisons to published studies. (Number of experiments to be determined). Vaudry D, et al, 2002. J Neurochem 83:1272-1284 Grumolato L, et al, 2003. Endocrinology 144:2368-2379

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Boolean modeling reveals the necessity of transcriptional regulation for bistablity in PC12 Cell Differentiation

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