Expression And Relation Of Beta-Catenin, PTEN Protein And TGF-beta₁ In Squamous Cell Carcinoma And Basal Cell Carcinoma

Background and objection:Both cutaneous squamous cell carcinoma (SCC) and basal cell carcinoma (BCC) are the most common skin tumors in human. However, the pathogenesis of these tumors is still largely unknown.Invasion and metastasis is one of the essential characters of malignant tumors. Before metastasizing to distance, tumor cells must firstly overcome the cell-cell adhesion.As one kind of multifunction protein,β-catenin (β-cat) was originally identified as a molecule capable of epithelial cell-cell adhesion by supporting the connection of actin bundles with E-cadhrin (E-cad). In this case, it has the ability of maintaining morph of normal cells and inhibiting invasion and metastasis of tumor cells. In addition,β-cat also can accumulate in cytoplasm and combine with T cell factor (TCF) and lymphoid enhancing factor (LEF) in nuclei, functioning as a core component of the Wnt signaling pathway. It has been known that the Wnt signaling pathway is relative to proliferation and metastasis of tumor cells. At the present,β-cat has been regarded as a hot spot in researching the mechanism of genesis and development of malignant tumors. Phosphatase and tensin homologue deleted on chromosome 10(PTEN) is a lipid phosphatase that acts a tumor suppressor by negatively controlling the phosphoinositide 3-kinase (PI3K) / protein kinase B (PKB) signaling pathway. Reports have showed that PTEN protein can maintain the E-cad/cat complexes in cytoplasmic membrane through interacting withβ-cat.Oppositing to PTEN protein, transforming growth factor beta₁ (TGF-β₁) can lead to the translocation ofβ-cat from cytoplasmic membrane to cytoplasm through phosphorylating the residues ofβ-cat. In normal epithelial tissues, TGF-β₁ acts as a tumor suppressor via growth inhibition whereas in advanced cancers promotes tumor progression via induction of tumor invasion. The molecular mechanisms through which TGF-β₁ shifts from a tumor suppressor to a tumor enhancer are poorly understood.To investigate the functions ofβ-cat, PTEN and TGF-β₁ proteins in SCC and BCC, this study examined the expression of three proteins in SCC (n=30), BCC (n=20) and normal skin tissues (n=25) by immunohistochemical SP, furthermore, analyzed the relationships between them. One new idea and method that can help to prevent and therapy those diseases was expected to be found.Materials and methods:Both 30 cases of SCC specimen and 20 cases of BCC specimen were obtained from the department of pathology of the first affiliated hospital of Zhengzhou university. The carcinoma tissues were collected from scalp, face, limbs and perineum in 24 male and 26 female patients in 2002 year to 2005 year. The extent of patients' age was from 25 to 88 years old(mean 56.22±17.41).As comparison,25 cases of human normal skin tissues specimen were acquired from non-carcinoma patients' full thick skin grafts of the department of plastic surgery of the first affiliated hospital of Zhengzhou university in 2004 year to 2005 year. According to WHO Class, there were 22 cases of grade1 SCC, 6 cases of grade2 SCC, 2 cases of grade3 SCC. Immunohistochemical SP method was adopted in this study. The known positive tissues were used as positive comparisons and PBS instead of the first antibody were used as negative comparison. The data was analyzed through package of software of SPSS 13.0, and a P value of less than 0.05 was considered statistically. Results:1. The expression ofβ-cat in SCC and BCC: Beta-cat mainly was located on cytoplasmic membrane in normal skin tissue. In SCC,β-cat accumulated in cytoplasm and nucleus instead of expressing on cytoplasmic membrane. Both the deficient expression in cytoplasmic membrane and the ectopic expression in cytoplasm and nucleus were more evident in SCC than those in normal skin tissues (P<0.050) . However, significant relationship weren't found between the aberrant expression ofβ-cat and the pathological grade of SCC (P=0.638>0.050) . In BCC, the expression ofβ-cat on cytoplasmic membrane reduced but markedly increased in cytoplasm and nucleus. The aberrant expression rates were higher in BCC than that in normal skin tissues (P=0.000<0.050) . but the deficient expression on cytoplasmic membrane were not lower than that in normal skin tissues(P> 0.050). The aberrant expression rates ofβ-cat weren't different between SCC and BCC (P=0.599>0.050) .2.The expression of PTEN protein in SCC and BCC: The positive immunostainirig of PTEN protein were mainly located in cytoplasm. The positive rates were 30.00%(9/30) in SCC, and that have no significant relationship with pathological grades of SCC (P=0.215 >0.050) .The positive rates were 60.00%(12/20) in BCC and 92.00% (23/25 ) in normal skin, respectively. The positive rates in normal skin tissues were higher than that in SCC and BCC (P=0.000<0.050, P=0.035<0.050) . And there were significant difference between SCC and BCC (P=0.035<0.050) .3.The expression of TGF-β₁ in SCC and BCC: The positive immunostaining of TGF-β₁ was mainly located in cytoplasm. The positive rates were 73.33% (22/30) in SCC, and there was no significant relationship with pathological grades of SCC(P=1.000>0.050). The positive rates were 45.00% (9/20 ) in BCC and 24.00% ( 6/25 ) in normal skin tissues, respectively. The positive rates in SCC were higher than that in BCC and normal skin tissue (P=0.043< 0.050, P=0.000< 0.050) and there were no significant difference between BCC and normal skin tissues( P=0.138 > 0.050).4. Correlative analysis: Correlative analysis showed the expression ofβ-cat on cytoplasmic membrane had a positive correlation with the expression of PTEN protein (P=0.003<0.050, r=0.419) and a negative correlation with the expression of TGF-β₁ (P=0.018<0.050, r=-0.381) in SCC and BCC. Meanwhile, the expression of PTENprotein were negative relative with the expression of TGF-β₁ (P=0.000<0.050, r=—0.503) .Conclusions:1. The abnormal distribution ofβ-cat, which leads to disruption of cell-cell adhesion and abnormal activation of Wnt signaling pathways, could play an important role in genesis and development of SCC, but haven't direct relationship with cells' differentiation.2. In spite of obvious accumulation ofβ-cat in cytoplasm and nucleus, deficiencies ofβ-cat in cytoplasmic membrane were still seldom in BCC. Those suggest that the genesis of BCC can't be directly caused by the disruption of cell-cell adhesion but the activation of Wnt signaling pathway.3. The absence of PTEN protein and the abnormal strong expression of TGF-β₁ could contribute to the genesis and development of SCC. But they have not evident relative with BCC and differentiation of SCC.4. The cooperation of absence of PTEN protein and abnormal strong expression of TGF-β₁, which promoted the aberrant expression ofβ-cat in cells, lead to proliferation and metastasis of SCC.