Abstract 5522: Cancer-associated point mutant in the START domain of DLC1 encodes a protein attenuated for tumor suppressor activity and for binding both Caveolin-1 and PLCD1 but not for Rho-GAP activity

Abstract Background DLC1, a tumor suppressor gene that is downregulated in many cancer types by genetic and nongenetic mechanisms, encodes a protein whose RhoGAP and scaffolding activities contribute to its tumor suppressor functions. The role of the DLC1 START (StAR-related lipid transfer; DLC1-START) domain, other than its binding to Caveolin-1, is poorly understood. In other START domains, a key function is that they bind lipids, but the putative lipid ligand for DLC1-START is unknown. Methods Lipid overlay assays and Phosphatidylserine (PS)-pull down assays confirmed the binding of DLC1-START to PS. Co-immunoprecipitation studies demonstrated the interaction between DLC1-START and Phospholipase C delta 1 (PLCD1) or Caveolin-1, and the contribution of PS to those interactions. Rho-GTP, cell proliferation, cell migration, and/or anchorage-independent growth assays were used to investigate the contribution of PS and PLCD1, or the implications of TCGA cancer-associated DLC1-START mutants, to DLC1 functions. Co-immunoprecipitations and PS-pull down assays were used to investigate the molecular mechanisms underlying the impaired functions of DLC1-START mutants. A structural model of DLC1-START was also built to better understand the structural implications of the cancer-associated mutations in DLC1-START. Results We identified PS as the lipid ligand for DLC1-START and determined that DLC1-START also binds PLCD1 protein in addition to Caveolin-1. PS binding contributes to the interaction of DLC1 with Caveolin-1 and with PLCD1. The importance of these activities for tumorigenesis is supported by our analysis of 7 cancer-associated DLC1-START mutants, each of which has reduced tumor suppressor function but retains wildtype RhoGAP activity. Our structural model of DLC1-START indicates the mutants perturb different elements within the structure, which is correlated with our experimental findings that the mutants are heterogenous with regard to the deficiency of their binding properties. Some have reduced PS binding, others reduced PLCD1 and Caveolin-1 binding, and others are deficient for all of these properties. Conclusion These observations highlight the importance of DLC1-START for the tumor suppressor function of DLC1 that is RhoGAP-independent. They also expand the versatility of START domains, as DLC1-START is the first found to bind PS, which promotes the binding to other proteins.

Download Full-text

Targeting the p53 tumor suppressor activity in glioblastomas using small molecule MDM2-inhibitor

Klinische Neurophysiologie ◽

10.1055/s-0031-1272660 ◽

2011 ◽

Vol 42 (01) ◽

Author(s):

P. Monfared ◽

T. Viel ◽

G. Schneider ◽

Y. Waerzeggers ◽

S. Rapic ◽

...

Keyword(s):

Tumor Suppressor ◽

Small Molecule ◽

Suppressor Activity ◽

P53 Tumor Suppressor ◽

Tumor Suppressor Activity ◽

Mdm2 Inhibitor

Download Full-text

Faculty Opinions recommendation of A tumor suppressor activity of Drosophila Polycomb genes mediated by JAK-STAT signaling.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.1168054.630168 ◽

2009 ◽

Author(s):

Ze'ev Paroush

Keyword(s):

Tumor Suppressor ◽

Suppressor Activity ◽

Stat Signaling ◽

Tumor Suppressor Activity

Download Full-text

Faculty Opinions recommendation of Polyhomeotic has a tumor suppressor activity mediated by repression of Notch signaling.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.1287964.755066 ◽

2009 ◽

Author(s):

Richard Fehon ◽

Julian Boggiano

Keyword(s):

Tumor Suppressor ◽

Notch Signaling ◽

Suppressor Activity ◽

Tumor Suppressor Activity

Download Full-text

Regulation of The Tumor Suppressor Activity of P53 In Human Breast Cancer

10.21236/ada383030 ◽

1999 ◽

Author(s):

James J. Manfredi

Keyword(s):

Breast Cancer ◽

Tumor Suppressor ◽

Human Breast Cancer ◽

Human Breast ◽

Suppressor Activity ◽

Tumor Suppressor Activity

Download Full-text

Merlin cooperates with neurofibromin and Spred1 to suppress the Ras–Erk pathway

Human Molecular Genetics ◽

10.1093/hmg/ddaa263 ◽

2020 ◽

Author(s):

Yan Cui ◽

Lin Ma ◽

Stephan Schacke ◽

Jiani C Yin ◽

Yi-Ping Hsueh ◽

...

Keyword(s):

Tumor Suppressor ◽

Binding Sites ◽

Neurofibromatosis Type ◽

Kinase Domain ◽

Erk Pathway ◽

Suppressor Activity ◽

The Third ◽

Tumor Suppressor Activity ◽

Multiple Signaling

Abstract The Ras–Erk pathway is frequently over-activated in human tumors. Neurofibromatosis type 1 and 2 (NF1, NF2) are characterized by multiple tumors of Schwann cell origin. The NF1 tumor suppressor neurofibromin is a principal Ras-GAP accelerating Ras inactivation, whereas the NF2 tumor suppressor merlin is a scaffold protein coordinating multiple signaling pathways. We have previously reported that merlin interacts with Ras and p120RasGAP. Here, we show that merlin can also interact with the neurofibromin/Spred1 complex via merlin-binding sites present on both proteins. Further, merlin can directly bind to the Ras-binding domain and the kinase domain of Raf1. As the third component of the neurofibromin/Spred1 complex, merlin cannot increase the Ras-GAP activity; rather, it blocks Ras binding to Raf1 by functioning as a ‘selective Ras barrier’. Merlin-deficient Schwann cells require the Ras–Erk pathway activity for proliferation. Accordingly, suppression of the Ras–Erk pathway likely contributes to merlin’s tumor suppressor activity. Taken together, our results, and studies by others, support targeting or co-targeting of this pathway as a therapy for NF2 inactivation-related tumors.

Download Full-text

JunB Breakdown in Mid-/Late G2 Is Required for Down-Regulation of Cyclin A2 Levels and Proper Mitosis

Molecular and Cellular Biology ◽

10.1128/mcb.01620-07 ◽

2008 ◽

Vol 28 (12) ◽

pp. 4173-4187 ◽

Cited By ~ 14

Author(s):

Rosa Farràs ◽

Véronique Baldin ◽

Sandra Gallach ◽

Claire Acquaviva ◽

Guillaume Bossis ◽

...

Keyword(s):

Cell Cycle ◽

Tumor Suppressor ◽

Genetic Instability ◽

S Phase ◽

Subsequent Reduction ◽

Suppressor Activity ◽

Cell Synchronization ◽

Tumor Suppressor Activity ◽

A Cell ◽

Cyclin A2

ABSTRACT JunB, a member of the AP-1 family of dimeric transcription factors, is best known as a cell proliferation inhibitor, a senescence inducer, and a tumor suppressor, although it also has been attributed a cell division-promoting activity. Its effects on the cell cycle have been studied mostly in G1 and S phases, whereas its role in G2 and M phases still is elusive. Using cell synchronization experiments, we show that JunB levels, which are high in S phase, drop during mid- to late G2 phase due to accelerated phosphorylation-dependent degradation by the proteasome. The forced expression of an ectopic JunB protein in late G2 phase indicates that JunB decay is necessary for the subsequent reduction of cyclin A2 levels in prometaphase, the latter event being essential for proper mitosis. Consistently, abnormal JunB expression in late G2 phase entails a variety of mitotic defects. As these aberrations may cause genetic instability, our findings contrast with the acknowledged tumor suppressor activity of JunB and reveal a mechanism by which the deregulation of JunB might contribute to tumorigenesis.

Download Full-text

Protein Phosphatase 2A Regulatory Subunit B56α Associates with c-Myc and Negatively Regulates c-Myc Accumulation

Molecular and Cellular Biology ◽

10.1128/mcb.26.7.2832-2844.2006 ◽

2006 ◽

Vol 26 (7) ◽

pp. 2832-2844 ◽

Cited By ~ 150

Author(s):

Hugh K. Arnold ◽

Rosalie C. Sears

Keyword(s):

Tumor Suppressor ◽

Protein Phosphatase ◽

Cell Function ◽

Cell Transformation ◽

Protein Phosphatase 2A ◽

Regulatory Subunit ◽

Suppressor Activity ◽

Tumor Suppressor Activity ◽

Structural Subunit ◽

Phosphatase 2A

ABSTRACT Protein phosphatase 2A (PP2A) plays a prominent role in controlling accumulation of the proto-oncoprotein c-Myc. PP2A mediates its effects on c-Myc by dephosphorylating a conserved residue that normally stabilizes c-Myc, and in this way, PP2A enhances c-Myc ubiquitin-mediated degradation. Stringent regulation of c-Myc levels is essential for normal cell function, as c-Myc overexpression can lead to cell transformation. Conversely, PP2A has tumor suppressor activity. Uncovering relevant PP2A holoenzymes for a particular target has been limited by the fact that cellular PP2A represents a large heterogeneous population of trimeric holoenzymes, composed of a conserved catalytic subunit and a structural subunit along with a variable regulatory subunit which directs the holoenzyme to a specific target. We now report the identification of a specific PP2A regulatory subunit, B56α, that selectively associates with the N terminus of c-Myc. B56α directs intact PP2A holoenzymes to c-Myc, resulting in a dramatic reduction in c-Myc levels. Inhibition of PP2A-B56α holoenzymes, using small hairpin RNA to knock down B56α, results in c-Myc overexpression, elevated levels of c-Myc serine 62 phosphorylation, and increased c-Myc function. These results uncover a new protein involved in regulating c-Myc expression and reveal a critical interconnection between a potent oncoprotein, c-Myc, and a well-documented tumor suppressor, PP2A.

Download Full-text