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Reduced expression of protein tyrosine phosphatase gamma in lung and ovarian tumors
1Department of Cell Biology and Histology, Faculty of Medical Sciences, University of Nijmegen, The Netherlands. C.Stolwijk@celbi.kun.nl
Abstract:
Based on LOH studies protein tyrosine phosphatasegamma (PTPgamma) has been suggested as a candidate tumor suppressor gene involved in the oncogenesis of lung and renal cancers. In order to assess the involvement of PTPgamma in tumor development we developed a PTPgamma-specific monoclonal antibody (gammaTL1) (IgM isotype) by immunization with a synthetic peptide of 15 amino acids corresponding to the amino acid sequence nos. 1423-1438 just outside the phosphatase domain-II. In line with the fact that the antibody was raised to an intracellular domain of the PTPgamma molecule the antibody labeled the cell membrane of fixed cells but did not stain the outside of the cell membrane in the immunofluorescence assay. The Mab gammaTL1 recognized a full-length baculovirus recombinant PTPgamma protein of 185 kDa, in addition to putative cleavage products of 120 kDa, 114/110 kDa and 80 kDa, on Western blots of lysates of PTPgamma-gene transfected Sf9 insect cells but not of tumor cell lysates. Based on immunoperoxidase and immunofluorescence assays on cryostat sections, however, PTPgamma was expressed in more than 90% of both normal, human tissue samples and in the (non-) tumor cells of carcinoma samples. However, PTPgamma was not found in 28% of the overall lung tumor samples, i.e. in 50% of the lung adenocarcinoma samples, while the expression was weak and heterogeneous in 71% of squamous lung cell carcinomas. PTPgamma was not suppressed in the normal cells between the lung carcinoma cells. The presence of PTPgamma, assayed by immunofluorescence in lung tumor cell lines (H69, H128, H82, C3) was confirmed by RT-PCR assay. Interestingly, the 90% expression score of PTPgamma protein in normal ovarian tissue samples was reduced dramatically to 44 and 38% in both the non-tumorous and tumorous cells, respectively, in ovarian tumor samples. PTPgamma was absent in the HT29 human colon carcinoma cell line both by immunofluorescence and RT-PCR assay. In summary, we have developed a PTPgamma-specific monoclonal antibody, that demonstrated that the expression of PTPgamma is severely reduced (>50%) in lung tumors and ovarian tumors.
Insights
Protein tyrosine phosphatase gamma (PTPgamma) is a potential tumor suppressor. A new PTPgamma-specific antibody revealed significantly reduced PTPgamma expression in lung and ovarian tumors, suggesting its role in cancer development.
Area of Science:
- Oncology
- Molecular Biology
- Immunology
Background:
- Protein tyrosine phosphatase gamma (PTPgamma) is implicated as a tumor suppressor gene in lung and renal cancers based on loss-of-heterozygosity (LOH) studies.
- Understanding PTPgamma's role in oncogenesis requires specific tools to assess its expression levels in tumor tissues.
Purpose of the Study:
- To develop a PTPgamma-specific monoclonal antibody (Mab gammaTL1) for assessing PTPgamma expression in various human cancers.
- To investigate the expression patterns of PTPgamma in normal and cancerous tissues, particularly lung and ovarian tumors.
Main Methods:
- Development of a PTPgamma-specific monoclonal antibody (Mab gammaTL1) using a synthetic peptide.
- Immunofluorescence and immunoperoxidase assays on cryostat sections of normal and tumor tissues.
- Western blot analysis of PTPgamma expression in transfected insect cells and tumor cell lysates.
- RT-PCR assays to confirm PTPgamma presence in lung tumor cell lines and colon carcinoma cell lines.
Main Results:
- Mab gammaTL1 recognized recombinant PTPgamma and its cleavage products.
- PTPgamma was highly expressed in normal human tissues (>90%).
- PTPgamma expression was significantly reduced in lung tumors (absent in 28%, weak/heterogeneous in 71% of squamous cell carcinomas) and ovarian tumors (reduced to 44% in non-tumorous and 38% in tumorous cells).
- PTPgamma was absent in the HT29 colon carcinoma cell line.
Conclusions:
- A novel PTPgamma-specific monoclonal antibody (Mab gammaTL1) was successfully developed.
- PTPgamma expression is severely reduced in lung and ovarian tumors, supporting its role as a tumor suppressor.
- These findings highlight the potential of PTPgamma as a biomarker or therapeutic target in specific cancers.