Original Article Morphoproteomic analysis reveals an overexpressed and constitutively activated phospholipase D1-mTORC2 pathway in endometrial carcinoma
Qi Shen, Melissa L Stanton, Wei Feng, Michelle E Rodriguez, Lois Ramondetta, Lei Chen, Robert E. Brown, Xiuzhen Duan
Department of Pathology and Laboratory Medicine, The University of Texas Medical School at Houston, Department of Pathology and Laboratory Medicine, The University of Texas MD Anderson Cancer Center, Department of Gynecologic Oncology, The University of Texas M.D. Anderson Cancer Center.
Received October 20, 2010; accepted November 9, 2010; Epub November 20, 2010; published January 1, 2011
Abstract: The mammalian target of rapamycin (mTOR) assembles into two distinct complexes: mTOR complex 1 (mTORC1) is predominantly cytoplasmic and highly responsive to rapamycin, whereas mTOR complex 2 (mTORC2) is both cytoplasmic and nuclear, and relatively resistant to rapamycin. mTORC1 and mTORC2 phosphorylatively regulate their respective downstream effectors p70S6K/4EBP1, and Akt. The resulting activated mTOR pathways stimulate protein synthesis, cellular proliferation, and cell survival. Moreover, phospholipase D (PLD) and its product, phosphatidic acid (PA) have been implicated as one of the upstream activators of mTOR signaling. In this study, we investigated the activation status as well as the subcellular distribution of mTOR, and its upstream regulators and downstream effectors in endometrial carcinomas (ECa) and non-neoplastic endometrial control tissue. Our data show that the mTORC2 activity is selectively elevated in endometrial cancers as evidenced by a predominant nuclear localization of the activated form of mTOR (p-mTOR at Ser2448) in malignant epithelium, accompanied by overexpression of nuclear p-Akt (Ser473), as well as overexpression of vascular endothelial growth factor (VEGF)-A isoform, the latter a resultant of target gene activation by mTORC2 signaling via hypoxia-inducible factor (HIF)-2alpha. In addition, expression of PLD1, one of the two major isoforms of PLD in human, is increased in tumor epithelium. In summary, we demonstrate that the PLD1/PA-mTORC2 signal pathway is overactivated in endometrial carcinomas. This suggests that the rapamycin-insensitive mTORC2 pathway plays a major role in endometrial tumorigenesis and that therapies designed to target the phospholipase D pathway and components of the mTORC2 pathway should be efficacious against ECa. (IJCEP1010005).
Address all correspondence to: Robert E. Brown, M.D. Department of Pathology and Laboratory Medicine University of Texas Health Science Center Medical School at Houston 6431 Fannin Street, MSB 2.286 Houston, TX 77030 Tel: 713-500-5332 Fax: 713-500-0695 E-mail: Robert.Brown@uth.tmc.edu