Evaluation of Metadherin Expression in Breast Cancer

Abstract

Metadherin gene (MTDH/ AEG-1/ Lyric) encodes a 582- aminoacid protein, metadherin (MTDH), which is almost undetectable by immunohistochemistry in normal breast tissue. MTDH expression is markedly increased in breast cancer cell lines as well as breast cancer patients which is found to be positively correlated with poor prognosis. The constitutive activation of PI3K/Akt/mTOR pathway triggers MTDH expression via GSK3β inactivation. In this thesis, the effect of PI-103 (dual PI3K/mTOR inhibitor) on MTDH expression in HER2+ breast cancer cell lines was investigated using qPCR and Western Blot. The results indicated different levels of inhibiton for MTDH expression in HER2 overexpressing cells. In MDA-MB-453 cells, incubation with PI-103 decreased MTDH mRNA and protein level significantly (p<0.05) which was considered in quite accordance with Akt dependency of these cells. MTDH mRNA expression decreased in SKBR-3 cells after 8 hours following a slight increase in 24 hours. The protein expression level was also affected moderately from PI-103. Taking into consideration the remarkable PTEN expression in these cells, we may speculate that decreased response to drug inhibitory effect of PI-103 may be attributed to the inverse corrrelation between MTDH protein level and PTEN activity. Finally, BT474 cells did not show significant change for MTDH at mRNA and protein level. In addition to cell lines, serum MTDH level of breast cancer patients (n=80) was evaluated by ELISA. Among molecular subtypes, HER2+ patients (n=9) had significantly high level of MTDH compared to patients diagnosed as Luminal A (n=20), and TNBC (n=32) (p<0.05) . There was no significant difference between HER2+ and Luminal B (n=19) subtypes. MTDH level was found significantly high in metastatic breast cancer (n=13) compared to nonmetastatic group (n=66) (p<0.01). In conclusion, PI3K/Akt targeting therapeutic strategies in HER2+ breast cancer may be involved in suppression of invasion and metastasis through regulation of MTDH expression.