Biomedical subjects

Marcus Buschbeck

Publications and source records attributed to Marcus Buschbeck.

7 recordsLinked to original sources

PubMed2006

The methyl-CpG binding protein MBD1 is required for PML-RARalpha function.

PML-RARalpha induces a block of hematopoietic differentiation and acute promyelocytic leukemia. This block is based on its capacity to inactivate target genes by recruiting histone deacetylase (HDAC) and DNA methyltransferase activities. Here we report that MBD1, a member of a conserved family of proteins able to bind methylated DNA, cooperates with PML-RARalpha in transcriptional repression and cellular transformation. PML-RARalpha recruits MBD1 to its target promoter through an HDAC3-mediated mechanism. Binding of HDAC3 and MBD1 is not confined to the promoter region but instead is spread over the locus. Knock-down of HDAC3 expression by RNA interference in acute promyelocytic leukemia cells alleviates PML-RAR-induced promoter silencing. We further demonstrate that retroviral expression of dominant-negative mutants of MBD1 in hematopoietic precursors compromises the ability of PML-RARalpha to block their differentiation and thus restored cell differentiation. Our results demonstrate that PML-RARalpha functions by recruiting an HDAC3-MBD1 complex that contributes to the establishment and maintenance of the silenced chromatin state.

Blotting, Western↗

PubMed2006

Strategies to overcome resistance to targeted protein kinase inhibitors in the treatment of cancer.

Inhibition of oncogenic protein kinases by small compound inhibitors has proven to be a valuable strategy for the directed and target-specific treatment of an ever-increasing number of cancer types. These include the treatment of chronic myeloid leukemia with the Bcr-Abl inhibitor imatinib and non-small-cell lung cancer with the epidermal growth factor inhibitors erlotinib and gefitinib. Unfortunately, initially successful therapy is often hampered by relatively rapid onset of resistance to the drug and subsequent relapse, particularly in patients with advanced disease. In the majority of cases this is caused by expansion of clones containing mutated forms of the targeted kinases, which confer insensitivity to the drug of the cancer cell. In addition, multiple factors including pharmacokinetic issues such as suboptimal drug delivery further contribute to resistance formation. Loss of target dependence due to the activation of parallel signaling pathways has also been reported as cause for acquired drug insensitivity. Here, we discuss currently applied as well as potential future strategies that can be applied to overcome and avoid resistance to drug therapy.

Antineoplastic Combined Chemotherapy Protocols↗

PubMed2005

Identification of a transcriptionally active hVH-5 pseudogene on 10q22.2.

Mitogen-activated protein kinases (MAPKs) are important regulators of a vast number of biological functions that affect life and death of eukaryotic cells and are tightly regulated by the concerted action of several phosphatases. Among these is the human homologue of vaccinia virus H1 phosphatase gene clone 5 (hVH-5) product, which dephosphorylates and thus inhibits members of the MAPK family. Here, we analyzed hVH-5 transcripts in mammary carcinoma cell lines and discovered a sequence with 88% similarity to hVH-5 transcripts. Because this variant of hVH-5 lacked intronic sequences in its genomic structure, we suggest it might be a processed pseudogene of hVH-5. psihVH-5 transcripts were detected in human peripheral tissues as well as in 11 of 14 breast cancer cell lines. In respect to the normal hVH-5 gene, the pseudogene contains several point mutations and a frame shift due to the deletion of 2 bases that would lead to the truncation of the putative psihVH-5 product.

Amino Acid Sequence↗

PubMed2005

Abl-kinase-sensitive levels of ERK5 and its intrinsic basal activity contribute to leukaemia cell survival.

It is well established that the mitogen-activated protein kinase (MAPK) signal is regulated through phosphorylation-dependent activation by the three-tiered MAPK cascade. However, our studies on the interaction of the MAPK ERK5 with the tyrosine kinase c-Abl and its oncogenic variants v-Abl and Bcr/Abl disclosed an alternative aspect of regulation. Independent of the MAPK cascade, Abl kinases were able to regulate the cellular amount of ERK5, at least in part, by stabilizing the protein. The resulting level of ERK5 and its intrinsic basal activity, but not necessarily its activation, were essential and sufficient to increase transformation by v-Abl and to mediate survival of Bcr/Abl-expressing leukaemia cells. These results suggest that the ability to regulate the cellular abundance of ERK5 contributes to the oncogenic potential of Abl kinases.

Animals↗

PubMed2004

The unique C-terminal tail of the mitogen-activated protein kinase ERK5 regulates its activation and nuclear shuttling.

ERK5 is unique among mitogen-activated protein kinases (MAPKs) in that it contains a large C-terminal tail. We addressed the question of how this tail could affect the signaling capacity of ERK5. Gradual deletion of the C-terminal domains resulted in a drastic increase of ERK5 kinase activity, which was dependent on the up-stream MAPK cascade, thus indicating a possible auto-inhibitory function of the tail. It is interesting that ERK5 was able to autophosphorylate its own tail. Moreover, ERK5, which was found to be expressed in virtually all kinds of cell lines, localized to nuclear as well as cytoplasmic compartments. The localization of ERK5 was determined by its C-terminal domains, which were also required for appropriate nucleocytoplasmic shuttling. Taken together, these results indicate that ERK5 signaling is directed by the presence of its unique C-terminal tail, which might be the key to understanding the key role of ERK5 in MAPK signaling.

Active Transport, Cell Nucleus↗

PubMed2003

Negative regulation of HER2 signaling by the PEST-type protein-tyrosine phosphatase BDP1.

Signaling by receptor tyrosine kinases (RTK) mediates a variety of complex cellular functions and in case of deregulation can contribute to pathophysiological processes. A tight and finely tuned control of RTK activity is therefore critical for the cell. We investigated the role of the PEST-type protein-tyrosine phosphatase BDP1 in the regulation of HER2, a member of the epidermal growth factor receptor (EGFR) family of RTKs. Here we demonstrate that HER2 signaling is highly sensitive to BDP1 activity. Overexpression of BDP1 inhibited ligand-induced activation of HER2 but not that of the closely related EGFR. On the other hand, suppression of endogenous BDP1 expression increased the phosphorylation state of HER2. In addition, BDP1 was able to interfere with downstream signaling events by inhibiting the phosphorylation of the adaptor protein Gab1 and reducing mitogen-activated protein kinase activation. Supported by the finding that BDP1 is coexpressed with HER2 in breast cancer cells, we suggest that BDP1 is an important regulator of HER2 activity and thus the first protein-tyrosine phosphatase shown to be involved in HER2 signal attenuation.

Adaptor Proteins, Signal Transducing↗

PubMed2002

Phosphotyrosine-specific phosphatase PTP-SL regulates the ERK5 signaling pathway.

The duration and the magnitude of mitogen-activated protein kinase (MAPK) activation specifies signal identity and thus allows the regulation of diverse cellular functions by the same kinase cascade. A tight and finely tuned regulation of MAPK activity is therefore critical for the definition of a specific cellular response. We investigated the role of tyrosine-specific phosphatases (PTPs) in the regulation of ERK5. Although unique in its structure, ERK5 is activated in analogy to other MAPKs by dual phosphorylation of threonine and tyrosine residues in its activation motif. In this study we concentrated on whether and how PTP-SL, a kinase-interacting motif-containing PTP, might be involved in the down-regulation of the ERK5 signal. We found that both proteins interact directly with each other in vitro and in intact cells, resulting in mutual modulation of their enzymatic activities. PTP-SL is a substrate of ERK5 and independent of phosphorylation binding to the kinase enhances its catalytic phosphatase activity. On the other hand, interaction with PTP-SL not only down-regulates endogenous ERK5 activity but also effectively impedes the translocation of ERK5 to the nucleus. These findings indicate a direct regulatory influence of PTP-SL on the ERK5 pathway and corresponding downstream responses of the cell.

Animals↗