The Role And Mechanism Of MTORC2in Adrenal Tumor

Background and Objective:The treatment of malignant pheochromocytoma (mPHEO) is very difficult. Currently,molecular targeting treatment has become a research hotspot for the treatment of mPHEO.mTOR kinase exists in two complexes called mTOR complex1(mTORC1) and mTORcomplex2(mTORC2). It has been demonstrated that mTORC1paly an important role inmPHEO. However, it is not clear whether mTORC2paly an important role in mPHEO. Toilluminate the role of mTORC2in mPHEO and investigate the inhibiting effect andmolecular mechanism by targetting the mTORC2can provide basic theory and guide fortargeting of the mTORC2in mPHEO treatment. In this study, we investigated the role andmechanism of mTORC2in mPHEO in vitro and vivo.Aldosterone-producing adenoma (APA) is one important factor of refractory hypertension,because of secretion of aldosterone. Thus, investigating the secretion mechanism is helpfulto realizing the disease of APA. In this study, we investigated the expression of rictor inthe tissue specimens of APA, and then evaluated the role of mTORC2in APA. In addition,adrenalectomy is usually recommended to improve blood pressure control in APA patients.Many investigators have suggested that hypokalemia is corrected in more than90%ofpatients with APA after adrenalectomy; however, an incomplete hypertension cure isfrequently observed. Therefore, we determined the factors affecting completehypertension cure in patients with APA after adrenalectomy.Materials and Methods:1Immunohistochemical method was used to investigate the expression of rictor in the tissue specimens of mPHEO.2The siRNA (small interfering RNA) was designed and used to down regulate theexpression of mTOR、Raptor and Rictor in PC12cell. We performed functional analysesof PC12cell such as cell proliferation, apoptosis, migration, and invasion assays throughdown regulation the expression of mTOR、Raptor and Rictor by RNA interference.3The signal pathway of PI3-K/AKT/mTORC1was analysed by western blot when theexpression of mTOR、 Raptor and Rictor was down regulated. The mechanism ofpromoting PC12cell apoptosis and preventing PC12cell migration and invasion was alsoinvestigated.4The nude mice with subcutaneous pheochromocytoma cell xenografts were treated withadministration of mTOR inhibitor by gavage. The change in tumor weight was compared.5Immunohistochemical method was used to investigate the expression of rictor in thetissue specimens of APA. The association of the expression of Rictor with the level ofaldosterone was analysed.6The factors affecting complete hypertension cure in patients with APA wereretrospectively analysed.Results:1Immunohistochemical staining of tissue sections demonstrated that Rictor werepredominantly expressed in the cytoplasm of mPHEO and benign tissues.2Both down regulation of Raptor and Rictor can inhibit the PC12cell proliferation, butdown regulation of mTOR can more effectively inhibit the PC12cell proliferation. Flowcytometric analysis found that down regulation of Raptor led to cell cycle arrest, but downregulation of Rictor led to apopotosis and prevent cell migration and invasion.3Down regulation of Raptor can decrease p-S6protein expression. p-AKT (Ser473) protein expression was decreased by down regulation of Rictor and mTOR, but increasedby down regutlation of Raptor. p-4EBP1protein expression was decreased by both downregulation of Raptor and Rictor, but more effectively decreased by down regulation ofmTOR. Down regulation of Rictor and mTOR can decrease Bcl-2protein expression, butincrease Bax protein expression. Down regulation of Rictor and mTOR can increaseE-cadherin protein expression, but decrease MMP2and MMP9protein expression.4Compared with Rap, PP242can more effectively inhibt the tumor growth in nude mice.5Immunohistochemical staining of tissue sections demonstrated that Rictor wereexpressed in the cytoplasm of APA tissues, but no association with the level ofaldosterone was found.6Only duration of hypertension and level of plasma aldosterone were the factors affectingcomplete hypertension cure after adrenalectomy for APA.Conclusions:1Targeting of mTORC2can promote PC12cell apoptosis and prevent migration andinvasion.2The best treatment options for mPHEO patients was combination targeting mTORC1and mTORC2.3That mTORC2play an important role in aldosterone secreation was not found.mTORC2may be play an important role in maintain the tumor proliferation.4Early diagnosis and early surgery are very important to avoid detrimental andirreversible effects on the cardiovascular system.