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Selective CREB-dependent cyclin expression mediated by the PI3K and MAPK pathways supports glioma cell proliferation.

Daniel P, Filiz G, Brown DV, Hollande F, Gonzales M, D'Abaco G, Papalexis N, Phillips WA, Malaterre J, Ramsay RG, Mantamadiotis T - Oncogenesis (2014)

Bottom Line: CREB overexpression in transgenic animals imparts oncogenic properties on cells in various tissues, and aberrant CREB expression is associated with tumours.Cyclin D1 is highly CREB-dependent, whereas cyclin B1 and PCNA are co-regulated by both CREB-dependent and -independent mechanisms.The precise regulatory network involved appears to differ depending on the tumour-suppressor phosphatase and tensin homolog status of the GBM cells, which in turn allows CREB to regulate the activity of the PI3K itself.

View Article: PubMed Central - PubMed

Affiliation: Department of Pathology, The University of Melbourne, Parkville, Victoria, Australia.

ABSTRACT
The cyclic-AMP response element binding (CREB) protein has been shown to have a pivotal role in cell survival and cell proliferation. Transgenic rodent models have revealed a role for CREB in higher-order brain functions, such as memory and drug addiction behaviors. CREB overexpression in transgenic animals imparts oncogenic properties on cells in various tissues, and aberrant CREB expression is associated with tumours. It is the central position of CREB, downstream from key developmental and growth signalling pathways, which gives CREB this ability to influence a spectrum of cellular activities, such as cell survival, growth and differentiation, in both normal and cancer cells. We show that CREB is highly expressed and constitutively activated in patient glioma tissue and that this activation closely correlates with tumour grade. The mechanism by which CREB regulates glioblastoma (GBM) tumour cell proliferation involves activities downstream from both the mitogen-activated protein kinase and phosphoinositide 3-kinase (PI3K) pathways that then modulate the expression of three key cell cycle factors, cyclin B, D and proliferating cell nuclear antigen (PCNA). Cyclin D1 is highly CREB-dependent, whereas cyclin B1 and PCNA are co-regulated by both CREB-dependent and -independent mechanisms. The precise regulatory network involved appears to differ depending on the tumour-suppressor phosphatase and tensin homolog status of the GBM cells, which in turn allows CREB to regulate the activity of the PI3K itself. Given that CREB sits at the hub of key cancer cell signalling pathways, understanding the role of glioma-specific CREB function may lead to improved novel combinatorial anti-tumour therapies, which can complement existing PI3K-specific drugs undergoing early phase clinical trials.

No MeSH data available.


Related in: MedlinePlus

Selective dependence of cyclin expression on CREB is determined by the PI3K pathway and tumour-suppressor PTEN status in glioma cells. (a, b) T98G and U118 cells were treated with either scramble or siCREB for 24 h before exposure to serum-free or serum conditions for 12 h. Cell lysate was then analysed for markers of PI3K activation. (c) U118 cells were treated with either LY294002, siCREB or both, and cell lysate was then immunoblotted for cyclin B1, cyclin D1 and PCNA expression changes. All western blottings were performed at least three times, and where applicable, total CREB and AKT were imaged, and then membranes were stripped and reprobed for pCREB and pAKT detection.
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fig6: Selective dependence of cyclin expression on CREB is determined by the PI3K pathway and tumour-suppressor PTEN status in glioma cells. (a, b) T98G and U118 cells were treated with either scramble or siCREB for 24 h before exposure to serum-free or serum conditions for 12 h. Cell lysate was then analysed for markers of PI3K activation. (c) U118 cells were treated with either LY294002, siCREB or both, and cell lysate was then immunoblotted for cyclin B1, cyclin D1 and PCNA expression changes. All western blottings were performed at least three times, and where applicable, total CREB and AKT were imaged, and then membranes were stripped and reprobed for pCREB and pAKT detection.

Mentions: To investigate the mechanism of the differential regulation of cyclin D1, cyclin B1 and PCNA by CREB in T98G compared with U118 cells, we looked at whether CREB knockdown affected upstream signalling components, given that previous studies have shown a link between CREB and upstream signalling components of the PI3K and MAPK pathways, such as insulin growth factor receptor (IGFR) and insulin receptor substrate-1/2 (IRS-1/2).31, 32 Crucially, T98G and U118 differ in PTEN status (T98G PTEN+ and U118 PTEN−), which may account for the differential CREB-mediated regulation of cell cycle factors via interaction with the MAPK and PI3K pathways.33, 34 Treatment of T98G cells with siCREB resulted in an almost complete block of AKT activation, which was not rescued by the addition of serum (Figure 6a). In comparison, CREB knockdown in U118 cells showed reduced AKT activation only in serum-free conditions (Figure 6b). Upon the addition of serum, AKT activation in U118 cells increased to levels identical to control cells (Figure 6b).


Selective CREB-dependent cyclin expression mediated by the PI3K and MAPK pathways supports glioma cell proliferation.

Daniel P, Filiz G, Brown DV, Hollande F, Gonzales M, D'Abaco G, Papalexis N, Phillips WA, Malaterre J, Ramsay RG, Mantamadiotis T - Oncogenesis (2014)

Selective dependence of cyclin expression on CREB is determined by the PI3K pathway and tumour-suppressor PTEN status in glioma cells. (a, b) T98G and U118 cells were treated with either scramble or siCREB for 24 h before exposure to serum-free or serum conditions for 12 h. Cell lysate was then analysed for markers of PI3K activation. (c) U118 cells were treated with either LY294002, siCREB or both, and cell lysate was then immunoblotted for cyclin B1, cyclin D1 and PCNA expression changes. All western blottings were performed at least three times, and where applicable, total CREB and AKT were imaged, and then membranes were stripped and reprobed for pCREB and pAKT detection.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4150215&req=5

fig6: Selective dependence of cyclin expression on CREB is determined by the PI3K pathway and tumour-suppressor PTEN status in glioma cells. (a, b) T98G and U118 cells were treated with either scramble or siCREB for 24 h before exposure to serum-free or serum conditions for 12 h. Cell lysate was then analysed for markers of PI3K activation. (c) U118 cells were treated with either LY294002, siCREB or both, and cell lysate was then immunoblotted for cyclin B1, cyclin D1 and PCNA expression changes. All western blottings were performed at least three times, and where applicable, total CREB and AKT were imaged, and then membranes were stripped and reprobed for pCREB and pAKT detection.
Mentions: To investigate the mechanism of the differential regulation of cyclin D1, cyclin B1 and PCNA by CREB in T98G compared with U118 cells, we looked at whether CREB knockdown affected upstream signalling components, given that previous studies have shown a link between CREB and upstream signalling components of the PI3K and MAPK pathways, such as insulin growth factor receptor (IGFR) and insulin receptor substrate-1/2 (IRS-1/2).31, 32 Crucially, T98G and U118 differ in PTEN status (T98G PTEN+ and U118 PTEN−), which may account for the differential CREB-mediated regulation of cell cycle factors via interaction with the MAPK and PI3K pathways.33, 34 Treatment of T98G cells with siCREB resulted in an almost complete block of AKT activation, which was not rescued by the addition of serum (Figure 6a). In comparison, CREB knockdown in U118 cells showed reduced AKT activation only in serum-free conditions (Figure 6b). Upon the addition of serum, AKT activation in U118 cells increased to levels identical to control cells (Figure 6b).

Bottom Line: CREB overexpression in transgenic animals imparts oncogenic properties on cells in various tissues, and aberrant CREB expression is associated with tumours.Cyclin D1 is highly CREB-dependent, whereas cyclin B1 and PCNA are co-regulated by both CREB-dependent and -independent mechanisms.The precise regulatory network involved appears to differ depending on the tumour-suppressor phosphatase and tensin homolog status of the GBM cells, which in turn allows CREB to regulate the activity of the PI3K itself.

View Article: PubMed Central - PubMed

Affiliation: Department of Pathology, The University of Melbourne, Parkville, Victoria, Australia.

ABSTRACT
The cyclic-AMP response element binding (CREB) protein has been shown to have a pivotal role in cell survival and cell proliferation. Transgenic rodent models have revealed a role for CREB in higher-order brain functions, such as memory and drug addiction behaviors. CREB overexpression in transgenic animals imparts oncogenic properties on cells in various tissues, and aberrant CREB expression is associated with tumours. It is the central position of CREB, downstream from key developmental and growth signalling pathways, which gives CREB this ability to influence a spectrum of cellular activities, such as cell survival, growth and differentiation, in both normal and cancer cells. We show that CREB is highly expressed and constitutively activated in patient glioma tissue and that this activation closely correlates with tumour grade. The mechanism by which CREB regulates glioblastoma (GBM) tumour cell proliferation involves activities downstream from both the mitogen-activated protein kinase and phosphoinositide 3-kinase (PI3K) pathways that then modulate the expression of three key cell cycle factors, cyclin B, D and proliferating cell nuclear antigen (PCNA). Cyclin D1 is highly CREB-dependent, whereas cyclin B1 and PCNA are co-regulated by both CREB-dependent and -independent mechanisms. The precise regulatory network involved appears to differ depending on the tumour-suppressor phosphatase and tensin homolog status of the GBM cells, which in turn allows CREB to regulate the activity of the PI3K itself. Given that CREB sits at the hub of key cancer cell signalling pathways, understanding the role of glioma-specific CREB function may lead to improved novel combinatorial anti-tumour therapies, which can complement existing PI3K-specific drugs undergoing early phase clinical trials.

No MeSH data available.


Related in: MedlinePlus