Our previous study revealed that two
splicing factors,
polypyrimidine tract-binding protein (PTB) and SRp20, were upregulated in
epithelial ovarian cancer (EOC) and knockdown of PTB expression inhibited ovarian
tumor cell growth and transformation properties. In this report, we show that knockdown of SRp20 expression in
ovarian cancer cells also causes substantial inhibition of
tumor cell growth and colony formation in soft
agar and the extent of such inhibition appeared to correlate with the extent of suppression of SRp20. Massive knockdown of SRp20 expression triggered remarkable apoptosis in these cells. These results suggest that overexpression of SRp20 is required for ovarian
tumor cell growth and survival. Immunohistochemical staining for PTB and SRp20 of two specialized tissue microarrays, one containing benign ovarian
tumors, borderline/low malignant potential (LMP) ovarian
tumors as well as invasive EOC and the other containing invasive EOC ranging from stage I to stage IV disease, reveals that PTB and SRp20 are both expressed differentially between benign
tumors and invasive EOC, and between borderline/LMP
tumors and invasive EOC. There were more all-negative or mixed staining cases (at least two evaluable section cores per case) in benign
tumors than in invasive EOC, whereas there were more all-positive staining cases in invasive EOC than in the other two disease classifications. Among invasive EOC, the majority of cases were stained all positive for both PTB and SRp20, and there were no significant differences in average staining or frequency of positive
cancer cells between any of the
tumor stages. Therefore, the expression of PTB and SRp20 is associated with
malignancy of ovarian
tumors but not with stage of invasive EOC.