Identification of calretinin and the alternatively spliced form calretinin-22k in primary pleural mesotheliomas and in their metastases

Background: Antibodies against calretinin represent an established, powerful and reliable immunohistochemical marker in the differential diagnosis between mesothelioma and adenocarcinomas. However, in studies published so far, the exact molecular identity of the immunoreactive protein(s) detected in mesothelioma sections has not yet been determined. Materials and Methods: Tissue biopsies from ten mesothelioma samples,, primary and metastatic, were analyzed by Western blot analysis and reverse transcriptase-polymerase chain reaction (RT-PCR), in addition to immunohistochemical staining. Results: Besides the selective positive immunoreaction in all 10 samples, calretinin was identified by Western blot analysis and by identification of its mRNA by RT-PCR. In addition, we identified the alternatively spliced form calretinin-22k and the corresponding mRNA, previously detected only in neoplastic cells in colon carcinomas and derived cell lines. Conclusion: Our findings demonstrate that the immunoreactivity observed in the mesotheliomas and their metastases investigated in this report is due to the concomitant presence of calretinin and the alternatively spliced form calretinin-22k.