Constitutive Overactivation of Phospholipase D1/mTORC2 Pathway in Endometrial Carcinomas
Q Shen, RE Brown, ML Stanton, X Duan. University of Texas Medical School at Houston, Houston, TX
Background: mTOR assembles into two complexes. mTORC1 is predominantly cytoplasmic and sensitive to rapamycin, whereas mTORC2 is abundant in both cytoplasm and nucleus, and relatively resistant to rapamycin. Previously we reported mTOR overactivation was consistently seen in endometrial carcinoma (ECa); this activation predominantly occurred in the nucleus, indicating an essential role for mTORC2, not mTORC1 signaling in endometrial tumorigenesis. In line with this, in clinical trials rapamycin shows efficacy against only a limited number of ECa. Recently phospholipase D (PLD) and its metabolite phosphatidic acid (PA) have been shown to regulate the mTOR signaling-binding of PA activates both mTORC1 and mTORC2; the effect of PA is competitive with rapamycin, with much higher concentrations of rapamycin needed to inhibit the PA-mTORC2 interaction than PA-mTORC1. In this study, we evaluated the expression of the two major PLD isoforms, PLD1 and PLD2, and one of the downstream effectors of mTORC2, p-Akt (Ser473) in ECa, proliferative (PE) and secretory endometrium (SE).
Design: A formalin-fixed paraffin-embedded tissue microarray containing 33 ECa, 24 PE, and 21 SE was constructed. IHC was used to detect PLD1, PLD2, and p-Akt (Ser473). Protein expression was quantified with light microscopy regarding staining pattern, cellular percentage and intensity.
Results: PLD1 expression is seen in both cytoplasm and nucleus. Moderate PLD1 expression is noted in 37% ECa but none in PE or SE; moreover, 71% PE and 71% SE show a complete lack of PLD1 expression. PLD2 expression is largely in the nucleus. No differences in the level of PLD2 expression are seen among the three groups. It is known mTORC1 phosphorylates p70S6K at Thr389, while mTORC2 phosphorylates Akt at Ser473. In line with our prior data showing predominant mTORC2 activation in ECa, expression of p-Akt (Ser473) is markedly increased in ECa compared to its non-cancerous counterparts: moderate to strong cytoplasmic and nuclear p-Akt (Ser473) staining is seen in 64% ECa vs 21% PE, and 5% SE. In contrast, there is no significant difference in expression of p-p70S6K (Thr389) among ECa, PE, or SE (prior data).
Conclusions: To our knowledge this is the first report of overexpression of PLD in ECa. Our data show the PLD1/mTORC2 pathway is constitutively overactivated in ECa, and suggest that suppressing PLD activity may represent a means for improving the efficacy of rapamycin in ECa, where the rapamycin-insensitive mTORC2 is the dominant driving force of tumorigenesis.
Monday, March 22, 2010 9:30 AM
Poster Session I Stowell-Orbison/Surgical Pathology/Autopsy Awards Poster Session # 224, Monday Morning