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Tuberous-sclerosis complex-related cell signaling in the pathogenesis of lung cancer

Angela Fuchs13*, Katharina König2, Lukas C Heukamp2, Jana Fassunke2, Jutta Kirfel3, Sebastian Huss5, Albert J Becker4, Reinhard Büttner2 and Michael Majores3

Author Affiliations

1 Department of Cardiology, Angiology and Pneumology, University of Bonn Medical School, Sigmund-Freud-Strasse 25, Bonn 53127, Germany

2 Institute of Pathology, University of Cologne, Kerpener Strasse 62, Köln 50937, Germany

3 Institute of Pathology, University of Bonn Medical School, Sigmund-Freud-Strasse 25, Bonn 53127, Germany

4 Institute of Neuropathology, University of Bonn Medical School, Sigmund-Freud-Strasse 25, Bonn 53127, Germany

5 Gerhard-Domagk-Institute of Pathology, University Hospital Münster, Albert-Schweitzer-Campus 1, Münster 48149, Germany

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Diagnostic Pathology 2014, 9:48  doi:10.1186/1746-1596-9-48

Published: 4 March 2014

Abstract

Background

Hamartin (TSC1) and tuberin (TSC2), encoded by the tuberous sclerosis complex (TSC) genes, form a tumor-suppressor heterodimer which is implicated in PI3K-Akt signaling and acts as a functional inhibitor of the mammalian target of rapamycin (mTOR). Dysregulation of mTOR has been assigned to carcinogenesis and thus may be involved in cancer development. We have addressed the role of hamartin, phospho-tuberin (p-TSC2) and phospho-mTOR (p-mTOR) in a series of non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC) samples.

Methods

We collected 166 NSCLC and SCLC samples for immunohistochemical studies and performed western blot analyses in NSCLC and SCLC cell lines as well as comparative analyses with EGFR phosphorylation and downstream effectors.

Results

In cell lines we found an inverse correlation between hamartin and p-mTOR expression. In surgical specimens cytoplasmic hamartin expression was observed in more than 50% of adenocarcinoma (AC) and squamous cell carcinoma (SCC) compared to 14% of SCLC. P-mTOR and p-TSC2 staining was found in a minority of cases.

There was a significant correlation between p-EGFR Tyr-1068, p-EGFR Tyr-992 and hamartin, and also between p-mTOR and p-EGFR Tyr-1173 in AC. In SCC an inverse correlation between hamartin and p-EGFR Tyr-992 was detected. Phosphorylation of TSC2 was associated with expression of MAP-Kinase. Hamartin, p-TSC2 and p-mTOR expression was not dependant of the EGFR mutation status. Hamartin expression is associated with poorer survival in SCC and SCLC.

Conclusions

Our findings confirm the inhibitory role of the tuberous sclerosis complex for mTOR activation in lung cancer cell lines. These results reveal hamartin expression in a substantial subset of NSCLC and SCLC specimens, which may be due to EGFR signaling but is not dependant on EGFR mutations. Our data provide evidence for a functional role of the tuberous sclerosis complex in lung cancer.

Virtual slides

The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/9274845161175223 webcite.

Keywords:
Tuberous sclerosis complex; TSC; EGFR; Hamartin; Tuberin; Lung cancer