Objective:
Tamoxifen (TAM) is an important selective estrogen receptor (ER) modulator for treatment of ER positive breast cancer. However, TAM is one risk factor for developing endometrial carcinoma (EnCa). This studyâs aim is to contribute towards our understanding of the molecular mechanisms of TAMâs tissue-specific contrary mode of action between mammary and endometrial tissues.
Materials-Methods:
To determine total and phosphorylated protein expression Immunoblotting was performed on endometrial tissues, and with TAM-treated EnCa and Mamma-Ca cell lines time kinetics were analyzed. Using molecular cloning and transfections, the PTEN status of RL95-2 EnCa cells was rescued.
Results:
We observed deregulation of phosphorylation within the IGF-AKT axis in endometrial tissues from patients with TAM therapy. Protein deregulations occurred in benign pre-stages of EnCa and included increased total protein and phosphorylation levels of ER, AKT, PTEN and mTOR. Kinetic studies following TAM treatment of the PTEN mutated RL95-2 EnCa cell line demonstrated induction of pERα-S118 and pAKT-T308. These effects occurred within minutes, pointing towards an additional non-genomic TAM mode of action. TAM treatment of four EnCa and MaCa cell lines, differing in their ER and PTEN statuses, was performed to compare PI3K-AKT-mTOR signaling with RL95-2 EnCa cells (ER+, PTEN-) showing highest levels of AKT activation following TAM treatment and the Mamma-Ca HTB-26 line (ER-, PTEN+) exhibiting lowest levels.
Conclusion:
We propose that following TAM treatment, the ER and PTEN status of a tissue dictates the level of AKT activation. Ongoing studies to re-express PTEN in RL95-2 cells will provide evidence for the role of PTEN in regulating the response upon TAM. Loss of PTEN occurs in ~80% of EnCa and could result in direct and rapid AKT activation upon TAM. Hence, low-molecular weight inhibitors blocking AKT activation could be an additional treatment benefit for patients under TAM therapy.
