**10. β-catenin**

The decisive factor in paradigm change regarding proteins with various compartments inside the cell and its relationship with the processes of disease establishment was β-catenin. The protein β-catenin is a transcriptional factor with nuclear function and also a structural component of tight junctions (adherens junctions) in the plasma membranes of the cell. The role of cell adhesion was the first to be characterized and such role is possible because βcatenin interacts with cadherins and with the actin cytoskeleton via an adapter protein αcatenin (Kemler, 1993)(Figure 1a). The transcriptional function developed as part of the intracellular pathways of the canonical Wnt. In the nucleus β-catenin acts as a cofactor along with TCF/LEF in the upregulation of a variety of oncogenes including cyclin D1 and c-myc (Figure 1d). The canonical Wnt/Wingless signaling pathway plays an important role in embryonic development and tumorigenesis (Morin, 1999; Polakis, 2000; Bienz, 2005).

The transcriptional role of β-catenin is very interesting because it involves translocation from the cytoplasm to the nucleus and initiates the expression of its target genes within it (Nusse, 1997; Akiyama, 2000). In the absence of Wnt binding a macromolecular complex formed by the cytoplasmic protein APC (adenomatous polyposis coli), Axin and disheveled (DSH) stimulate the phosphorylation of β-catenin. Directly responsible for this phosphorylation is the protein casein kinase 1 (CK1) and glycogen synthase kinase 3 (GSK3). Β-catenin phosphorylated is destined to a ubiquitin-mediated degradation of β-catenin (Figure 1 b). So, in the absence of Wnt signaling levels of β-catenin are kept low by the action of Gsk3 and CK1 (Clevers, 2006; McDonald et al., 2009).

Translocation of β-catenin only happens when the receptors of the canonical Wnt pathways are activated and the macromolecular complex is recruited to the plasma membrane proteins with CK1 and GSK3 and thus could not phosphorylate β-catenin (Figure 1 c). The key point in this model is that the activation of canonical pathway leads to stabilization of β catenin. Therefore, Wnt signaling would finally prevent β-catenin degradation, which could then translocate to the nucleus and perform its transcriptional activity (Clevers, 2006). As we

(Kanczuga-koda et al., 2006). The important diagnostic value of IMH is evident in the

Although the role of connexins in the process of metastasis is controversial because some studies indicate that connexin expression is inversely proportional to metastatic capacity of a primary tumor (Nicolson et al., 1988), other studies reveal that connexins might be

At least it is clear that, unlike previously thought, connexins have a tumor suppressor function, but not from a classical point of view, since there are no mutations of this protein associated with carcinogenesis. So, they seem to have different effects on different stages of carcinogenesis, (depending on the connexin isoform or cell type in which it is expressed). Connexins seem to favor cell proliferation when they are downregulated (cytoplasmic localization) and increase the potential for invasion and metastasis when they are overexpressed (initially in the plasma membrane) (for a review of this literature sees Crespin et al., 2008). As we shall see at the end of this chapter, this issue needs to be clarified for a better understanding of subcellular compartmentalization and mechanisms of

The decisive factor in paradigm change regarding proteins with various compartments inside the cell and its relationship with the processes of disease establishment was β-catenin. The protein β-catenin is a transcriptional factor with nuclear function and also a structural component of tight junctions (adherens junctions) in the plasma membranes of the cell. The role of cell adhesion was the first to be characterized and such role is possible because βcatenin interacts with cadherins and with the actin cytoskeleton via an adapter protein αcatenin (Kemler, 1993)(Figure 1a). The transcriptional function developed as part of the intracellular pathways of the canonical Wnt. In the nucleus β-catenin acts as a cofactor along with TCF/LEF in the upregulation of a variety of oncogenes including cyclin D1 and c-myc (Figure 1d). The canonical Wnt/Wingless signaling pathway plays an important role in

embryonic development and tumorigenesis (Morin, 1999; Polakis, 2000; Bienz, 2005).

action of Gsk3 and CK1 (Clevers, 2006; McDonald et al., 2009).

The transcriptional role of β-catenin is very interesting because it involves translocation from the cytoplasm to the nucleus and initiates the expression of its target genes within it (Nusse, 1997; Akiyama, 2000). In the absence of Wnt binding a macromolecular complex formed by the cytoplasmic protein APC (adenomatous polyposis coli), Axin and disheveled (DSH) stimulate the phosphorylation of β-catenin. Directly responsible for this phosphorylation is the protein casein kinase 1 (CK1) and glycogen synthase kinase 3 (GSK3). Β-catenin phosphorylated is destined to a ubiquitin-mediated degradation of β-catenin (Figure 1 b). So, in the absence of Wnt signaling levels of β-catenin are kept low by the

Translocation of β-catenin only happens when the receptors of the canonical Wnt pathways are activated and the macromolecular complex is recruited to the plasma membrane proteins with CK1 and GSK3 and thus could not phosphorylate β-catenin (Figure 1 c). The key point in this model is that the activation of canonical pathway leads to stabilization of β catenin. Therefore, Wnt signaling would finally prevent β-catenin degradation, which could then translocate to the nucleus and perform its transcriptional activity (Clevers, 2006). As we

resolution stage of the disease.

involved in metastasis (Carystinos et al., 2001).

regulation of intracellular signaling.

**10. β-catenin** 

shall see later, this classical interpretation may change when additional information on subcellular compartmentalization is gained.

In clinical practice aberrant changes in the expression of β-catenin in the nucleus have made it possible to suggest the use of this molecule as a complement to the differential diagnosis of various cancers, including cancers of the gastrointestinal tract, lung and tumors of gynecological origin (Montgomery & Folpe, 2005). Also, the absence or loss of nuclear expression of β-catenin expression associated with strong cytoplasmic P-cadherin was associated with melanoma aggressiveness and poor patient survival, establishing an important prognostic value in these types of cancer for β-catenin (Bachmann et al., 2005).

Fig. 1. Canonical and non-canonical Wnt signaling pathway. Crosstalk between Kaiso, Kaiso–p120ctn, β-catenin and Endossomal compartments. a. In the absence of Wnt ligands or in the case of high E-cadherin concentrations, β-catenin and p120ctn associate with Ecadherin, promoting intercellular adhesion. b. In the absence of Wnt binding, a macromolecular complex formed by the cytoplasmic protein APC (adenomatous polyposis coli), Axin and disheveled (DSH) stimulate the phosphorylation of β-catenin. Directly responsible for this phosphorylation is the protein casein kinase 1 (CK1) and glycogen synthase kinase 3 (GSK3). Β-catenin phosphorylated is destined to a ubiquitin-mediated degradation of β-catenin. c. The activation of canonical pathway leads to stabilization of β catenin. Therefore, Wnt signaling would finally prevent β-catenin degradation, which could then (d.) translocate to the nucleus, and perform its transcriptional activity, associate with lymphoid enhancer-binding protein (LEF)/T-cell factor (TCF). e. If E-cadherin is mutated or

Kaiso and Prognosis of Cancer in the Current Epigenetic Paradigm 117

The genes transcriptionally regulated by Kaiso are matrilysin (Spring et al., 2005), c-myc and cyclin D1 (Van Roy & McCrea, 2005), all of them widely known for their involvement in cell proliferation and metastasis and all also regulated by the domain "Zinc finger" of Kaiso (Daniel, 2007). Gene Wnt11 is another important and well- known regulatory target, which

The non-canonical Wnt pathways are involved in cell polarity and cell movements of epithelial-mesenchymal transition observed during gastrulation, and also during the process of metastasis (Wallingford et al., 2002; Veeman et al., 2003). The cytoplasmic molecules involved in the transduction of non-canonical Wnt pathway are DSH (Dishevelled) and DAAM1 (Dishevelled-associated activator of morphogenesis 1) (Habas et al., 2001) that through two independent and parallel pathways lead to activation of GTPases, Rho (Marlow et al., 2002; Habas et al., 2001) and Rac (Habas et al., 2003)(Figure 1 e). Ultimately, the activation of a kinase assorted to the Rho called ROCK would be responsible for the reorganization of the cytoskeleton (Veeman et al., 2003). p120ctn regulates the cell cytoplasm proteins Rho and Rac (Van Roy & McCrea, 2005) and Kaiso would be indirectly related to processes that involve reorganization of the cytoskeleton

The Kaiso protein, unlike other members of the subfamily, appears to be the only factor with bimodal features in their interaction with DNA, being able to interact specifically with methylated CpG island sites and with consensus DNA sequences CTGCNA (Prokhortchouk et al., 2001; Daniel et al., 2002) (Figure 1 f). These interactions are important for the epigenetic silencing of tumor suppressor genes, which is an essential role of Kaiso in colon

Regarding epigenetic silencing, the Kaiso protein also acts as a histone-deacetylasedependent transcriptional repressor (Daniel, 2007). The HDAC (histone deacetylase) catalyzes the deacetylation of histones and these changes facilitate more closed chromatin conformation and restrict gene transcription. The HDAC acts as a protein complex with corepressors recruited. Some of them are directly recruited by Kaiso as NCOR1 (nuclear receptor co-repressor 1) (Yoon et al., 2003) and SIN3A (Van Roy & McCrea, 2005) (Figure 1f). The information on repression of target genes of the canonical and non-canonical Wnt pathways, associated with cancer (including matrilysin and Wnt11) can lead us to think that

Almost all the members of the POZ-ZF family were found to be involved in cancer development. BCL-6 and PLZF are oncoproteins linked to non-Hodgkin's lymphoma and acute promyelocytic leukemia, respectively (Chen et al., 1994; Onizuka et al., 1995). FAZF and ZBTB7 are related to Fanconi's anemia and several other human cancers (Hoatlin et al., 1999; Maeda et al., 2005b; Dai et al., 2002; Pessler et al., 1997). On the other hand, ICH-6 and APM1 are candidate tumor suppressors in various human cancers (Schneider et al., 1997;

Like other members of the subfamily POZ-ZF, the Kaiso protein has been implicated in cancer and the first indirect evidence emerged because the target genes of the Kaiso protein

belongs to the non-canonical Wnt pathways (Kim et al., 2004).

cancer development processes (Lopes et al., 2008).

**12. Kaiso and tumorigenesis** 

Albagli, 2003).

the role of Kaiso in the healthy cell is that of a tumor suppressor gene.

during metastasis.

downregulated, p120ctn become at least partly cytoplasmic. Cytoplasmic p120ctn is stable and modulates small GTPases by stimulating RAC and inhibiting RHO. Both small GTPases are stimulated by non-canonical Wnt signalling. f. Kaiso translocate into the nucleus and within the nucleus kaiso associates with co-repressors (N-CoR) and histone deacetylases (HDAC) and represses genes harbouring KBS (Kaiso-binding sites) or methylated CpG (mCpG) islands in their regulatory domain. Likewise, a NCoR complex with lymphoid enhancer-binding protein (LEF)/T-cell factor (TCF) represses genes with a LEF binding sequence (LBS). g. Translocation of Kaiso in the nucleus and vice versa is mainly under the influence of microenvironmental factors. h. The protein complexes involving the Wnt receptor, Gsk3 and CK1 (among others), are then taken inside the lumen of the multivesicular bodies (MVBs), separating Gsk3 from their cytoplasmic substrates and it also produces the stabilization of β-catenin. APC, adenometous polyposis coli protein; BTB/POZ, broad-complex, tramtrak and bric-a-brac/poxvirus and zinc finger domain; DAAM1, Dishevelled-associated activator of morphogenesis 1; GBP, GSK3-binding protein; LRP, LDL-receptor-related protein (Wnt co-receptor). Wnt signalling pathway modified from Van Roy & McCrea, 2005.
