Aberrant Calreticulin Expression Is Involved in the Dedifferentiation of Dedifferentiated Liposarcoma
Masanori Hisaoka, Atsuji Matsuyama. University of Occupational and Environmental Health, Kitakyushu, Japan
Background: Liposarcomas are a representative group of soft tissue sarcomas with variably hampered adipogenesis, which is most exemplified by its dedifferentiated subtype. Despite some characteristic genetic alterations harbored in the subtype, the factors responsible for inhibiting the adipocytic differentiation remains unknown. A recent gene expression profiling study has identified several unique genes that are highly expressed in dedifferentiated liposarcoma, and the gene encoding calreticulin, a major Ca2+-buffering protein that can inhibit adipocytic differentiation, was found to be overexpressed.
Design: We investigated the expression of calreticulin in 45 liposarcomas including 15 dedifferentiated tumors at both the protein and mRNA levels, and compared the levels to those in lipomas and normal fat. The anti-adipogenic function of calreticulin was assessed using a dedifferentiated liposarcoma cell line, FU-DDLS-1, by transfection of siRNA. Fluorescence in situ hybridization (FISH) and quantitative reversed transcription-polymerase chain reaction (RT-PCR) for putative microRNAs (miRNAs) targeting calreticulin were performed to address potential genetic and epigenetic alterations in the calreticulin gene (CALR).
Results: Immunohistochemically, calreticulin was consistently expressed in dedifferentiated areas of dedifferentiated liposarcomas and commonly in atypical stromal cells and/or lipoblasts in their well differentiated areas (87%), whereas large vacuolated adipocytic cells in the tumors or normal fat were essentially negative. The results were further supported by the findings of Western blotting and quantitative RT-PCR analyses. Although abnormalities in 19p13.1-13.2, where CALR is localized, were uncommon in the dedifferentiated liposarcomas examined by FISH, the expression of miR-1257, which was extracted by a computational prediction software program, was significantly suppressed in the dedifferentiated subtype. The downregulation of calreticulin by siRNA could induce adipogenesis in dedifferentiated liposarcoma cells and reduce the cell proliferation.
Conclusions: Our results suggest that calreticulin is aberrantly expressed in dedifferentiated liposarcoma and is involved in its dedifferenitation and/or tumor progression.
Category: Bone & Soft Tissue
Monday, March 19, 2012 1:00 PM
Poster Session II # 5, Monday Afternoon