Biomedical subjects

Karin Kroboth

Publications and source records attributed to Karin Kroboth.

4 recordsLinked to original sources

PubMed2007

Loss of APC induces polyploidy as a result of a combination of defects in mitosis and apoptosis.

Mutations in the adenomatous polyposis coli (APC) tumor suppressor gene initiate a majority of colorectal cancers. Acquisition of chromosomal instability is an early event in these tumors. We provide evidence that the loss of APC leads to a partial loss of interkinetochore tension at metaphase and alters mitotic progression. Furthermore, we show that inhibition of APC in U2OS cells compromises the mitotic spindle checkpoint. This is accompanied by a decrease in the association of the checkpoint proteins Bub1 and BubR1 with kinetochores. Additionally, APC depletion reduced apoptosis. As expected from this combination of defects, tetraploidy and polyploidy are consequences of APC inhibition in vitro and in vivo. The removal of APC produced the same defects in HCT116 cells that have constitutively active beta-catenin. These data show that the loss of APC immediately induces chromosomal instability as a result of a combination of mitotic and apoptotic defects. We suggest that these defects amplify each other to increase the incidence of tetra- and polyploidy in early stages of tumorigenesis.

Adenomatous Polyposis Coli Protein↗

PubMed2006

Lack of adenomatous polyposis coli protein correlates with a decrease in cell migration and overall changes in microtubule stability.

Most sporadic colorectal tumors carry truncation mutations in the adenomatous polyposis coli (APC) gene. The APC protein is involved in many processes that govern gut tissue. In addition to its involvement in the regulation of beta-catenin, APC is a cytoskeletal regulator with direct and indirect effects on microtubules. Cancer-related truncation mutations lack direct and indirect binding sites for microtubules in APC, suggesting that loss of this function contributes to defects in APC-mutant cells. In this study, we show that loss of APC results in disappearance of cellular protrusions and decreased cell migration. These changes are accompanied by a decrease in overall microtubule stability and also by a decrease in posttranslationally modified microtubules in the cell periphery particularly the migrating edge. Consistent with the ability of APC to affect cell shape, the overexpression of APC in cells can induce cellular protrusions. These data demonstrate that cell migration and microtubule stability are linked to APC status, thereby revealing a weakness in APC-deficient cells with potential therapeutic implications.

Acetylation↗

PubMed2004

Transcriptional regulation by the repressor of estrogen receptor activity via recruitment of histone deacetylases.

Histone acetyltransferases and deacetylases are recruited by transcription factors and adapter proteins to regulate specific subsets of target genes. We were interested in identifying interaction partners of histone deacetylase 1 (HDAC1) that might be involved in conferring target or substrate specificity. Using the yeast two-hybrid system, we isolated the repressor of estrogen receptor activity (REA) as a novel HDAC1-associated protein. We demonstrated the in vivo interaction of REA with HDAC1 and characterized the respective domains required for their interaction in vitro. In addition, we found that REA also associates with the class II histone deacetylase HDAC5. In luciferase reporter assays, REA decreased transcription, and this repression was sensitive to the deacetylase inhibitor trichostatin A. Finally, we showed that REA specifically interacts with the chicken ovalbumin upstream binding transcription factors and II. The nuclear receptor chicken ovalbumin upstream binding transcription factor I was found to cooperate with REA and histone deacetylases in the repression of target genes. We, therefore, propose a novel function for REA as a mediator of transcriptional repression by nuclear hormone receptors via recruitment of histone deacetylases.

3T3 Cells↗

PubMed2002

Alternate activation of two divergently transcribed mouse genes from a bidirectional promoter is linked to changes in histone modification.

Thymidine kinase (TK) is a growth factor-inducible enzyme that is highly expressed in proliferating mammalian cells. Expression of mouse TK mRNA is controlled by transcriptional and posttranscriptional mechanisms including antisense transcription. Here we report the identification of a novel gene that is divergently transcribed from the bidirectional TK promoter. This gene encodes kynurenine formamidase (KF), an enzyme of the tryptophan metabolism. Whereas the TK gene is induced upon interleukin-2-mediated activation of resting T cells, the KF gene becomes simultaneously repressed. The TK promoter is regulated by E2F, SP1, histone acetyltransferases, and deacetylases. The binding site for the growth-regulated transcription factor E2F is beneficial for TK promoter activity but not required for KF expression. In contrast, the SP1 binding site is crucial for transcription in both directions. Inhibition of histone deacetylases by trichostatin A leads to increased histone acetylation at the TK/KF promoter and thereby to selective activation of the TK promoter and simultaneous shut-off of KF expression. Similarly, TK gene activation by interleukin-2 is linked to histone hyperacetylation, whereas KF expression correlates with reduced histone acetylation. The KF gene is the rare example of a mammalian gene whose expression is linked to histone hypoacetylation at its promoter.

Acetylation↗