1.
Jögi, Annika, et al.
(författare)
Hypoxia alters gene expression in human neuroblastoma cells toward an immature and neural crest-like phenotype.
2002
Ingår i: Proceedings of the National Academy of Sciences. - : Proceedings of the National Academy of Sciences. - 1091-6490 .- 0027-8424. ; 99:10, s. 7021-7026
Tidskriftsartikel (refereegranskat) abstract
Insufficient oxygen and nutrient supply often restrain solid tumor growth, and the hypoxia-inducible factors (HIF) 1 alpha and HIF-2 alpha are key transcription regulators of phenotypic adaptation to low oxygen levels. Moreover, mouse gene disruption studies have implicated HIF-2 alpha in embryonic regulation of tyrosine hydroxylase, a hallmark gene of the sympathetic nervous system. Neuroblastoma tumors originate from immature sympathetic cells, and therefore we investigated the effect of hypoxia on the differentiation status of human neuroblastoma cells. Hypoxia stabilized HIF-1 alpha and HIF-2 alpha proteins and activated the expression of known hypoxia-induced genes, such as vascular endothelial growth factor and tyrosine hydroxylase. These changes in gene expression also occurred in hypoxic regions of experimental neuroblastoma xenografts grown in mice. In contrast, hypoxia decreased the expression of several neuronal/neuroendocrine marker genes but induced genes expressed in neural crest sympathetic progenitors, for instance c-kit and Notch-1. Thus, hypoxia apparently causes dedifferentiation both in vitro and in vivo. These findings suggest a novel mechanism for selection of highly malignant tumor cells with stem-cell characteristics.
2.
Jögi, Annika, et al.
(författare)
Modulation of Basic Helix-Loop-Helix Transcription Complex Formation by Id Proteins during Neuronal Differentiation.
2002
Ingår i: Journal of Biological Chemistry. - 1083-351X. ; 277:11, s. 9118-9126
Tidskriftsartikel (refereegranskat) abstract
It is assumed that the Id helix-loop-helix (HLH) proteins act by associating with ubiquitously expressed basic HLH (bHLH) transcription factors, such as E47 and E2-2, which prevents these factors from forming functional hetero- or homodimeric DNA binding complexes. Several tissue-specific bHLH proteins, including HASH-1, dHAND, and HES-1, are important for development of the nervous system. Neuroblastoma tumors are derived from the sympathetic nervous system and exhibit neural crest features. In differentiating neuroblastoma cells, HASH-1 is down-regulated, and there is coincident up-regulation of the transcriptional repressor HES-1, which is known to bind the HASH-1 promoter. We found that the three Id proteins expressed in neuroblastoma cells (Id1, Id2, and Id3) were down-regulated during induced differentiation, indicating that Id proteins help keep the tumor cells in an undifferentiated state. Studying interactions, we noted that all four Id proteins could dimerize with E47 or E2-2, but not with HASH-1 or dHAND. However, the Id proteins did complex with HES-1, and increased levels of Id2 reduced the DNA binding activity of HES-1. Furthermore, HES-1 interfered with Id2/E2-2 complex formation. The ability of Id proteins to affect HES-1 activity is of particular interest in neuronal cells, where regulation of HES-1 is essential for the timing of neuronal differentiation.
3.
Jögi, Annika
(författare)
Transcriptional regulation in neuroblastoma cells under normoxic and hypoxic conditions
2002
Doktorsavhandling (övrigt vetenskapligt/konstnärligt) abstract
The childhood malignancy neuroblastoma develops from early cells of the sympathetic nervous system (SNS), and the tumors often produce catecholamines. Neuroblastoma cells retain several characteristics of immature sympathetic cells including the expression of a number of transcription factors normally expressed during embryogenesis. The genesis of the SNS requires the correct expression pattern of several transcription factors of the basic helix-loop-helix (bHLH) family, such as HASH-1 a pro-neuronal gene. HASH-1 expression is negatively regulated by another bHLH factor, HES-1. In these studies, we show that HASH-1 form transcription activating dimers with the ubiquitously expressed bHLH factor E2-2 in neuroblastoma cells. Furthermore, we establish that the Id proteins, which lack the basic DNA-binding domain and act as dominant negative inhibitors in the bHLH network, bind to HES-1. By dimerization with HES-1 the Id proteins may act to repress the HES-1 mediated transcriptional repression. In addition, HES-1 can alleviate the negative effect of Id proteins on bHLH factor induced transcription, by sequestration of Id. These findings reveal a novel regulatory level of the bHLH network. Solid tumors most often contain regions with impaired circulation and hypoxia. Two transcription factors of the bHLH/PAS subgroup, the hypoxia inducible factors HIF-1a and HIF-2a, are key regulators of the cellular response to oxygen deprivation. Interestingly, HIF-2a is also expressed in the developing SNS and required for catecholamine production, and HIF-2a deficient mice die with bradycardia before birth. The dual implications of HIF-2a in neuroblastoma tumors, involvement in SNS development as well as in adaptation to the tumor microenvironment , prompted us to investigate how neuroblastoma cells respond to growth under hypoxic conditions. Unexpectedly, we found that hypoxia (1% oxygen) drive the neuroblastoma cells toward an immature and neural crest-like phenotype. Several neuronal and neuroendocrine marker genes, such as chromogranin A/B, NPY, and HASH-1, were down-regulated in response to oxygen deprivation, whereas a number of genes expressed during early neural crest development were up-regulated, examplified by c-kit, Notch-1, and Id2. To further delineate the the hypoxic phenotype of human neuroblastoma cells, we have analyzed their gene expression after 72 h exposure to hypoxia employing microarray analysis harboring 35 000 clones. Almost one percent of the represented transcripts were up-regulated more than three-fold and about 0.5 % were down-regulated more than three-fold in response to hypoxia. The microarray results strenghten our view of hypoxic neuroblastoma cells as less mature. To test whether hypoxia-induced dedifferentiation is a neuroblastoma specific event or may occur also in other solid tumors, we have analyzed a panel of ductal breast carcinoma in situ. Also in these tumors, were hypoxia associated with a less mature phenotype of the tumor cells. We propose hypoxia-induced dedifferentiation as one means by which intra-tumor hypoxia drives tumor propagation.
