MUC1-associated proliferation signature predicts outcomes in lung adenocarcinoma patients

Abstract

Background: MUC1 protein is highly expressed in lung cancer. The cytoplasmic domain of MUC1 (MUC1-CD) induces tumorigenesis and resistance to DNA-damaging agents. We characterized MUC1-CD-induced transcriptional changes and examined their significance in lung cancer patients.

Methods: Using DNA microarrays, we identified 254 genes that were differentially expressed in cell lines transformed by MUC1-CD compared to control cell lines. We then examined expression of these genes in 441 lung adenocarcinomas from a publicly available database. We employed statistical analyses independent of clinical outcomes, including hierarchical clustering, Student's t-tests and receiver operating characteristic (ROC) analysis, to select a seven-gene MUC1-associated proliferation signature (MAPS). We demonstrated the prognostic value of MAPS in this database using Kaplan-Meier survival analysis, log-rank tests and Cox models. The MAPS was further validated for prognostic significance in 84 lung adenocarcinoma patients from an independent database.

Results: MAPS genes were found to be associated with proliferation and cell cycle regulation and included CCNB1, CDC2, CDC20, CDKN3, MAD2L1, PRC1 and RRM2. MAPS expressors (MAPS+) had inferior survival compared to non-expressors (MAPS-). In the initial data set, 5-year survival was 65% (MAPS-) vs. 45% (MAPS+, p < 0.0001). Similarly, in the validation data set, 5-year survival was 57% (MAPS-) vs. 28% (MAPS+, p = 0.005).

Conclusions: The MAPS signature, comprised of MUC1-CD-dependent genes involved in the control of cell cycle and proliferation, is associated with poor outcomes in patients with adenocarcinoma of the lung. These data provide potential new prognostic biomarkers and treatment targets for lung adenocarcinoma.

Figure 1

Differentially expressed genes in MUC1 transfected cells. A. Expressional clustering of genes expressed at least two-fold differently in (a) MUC1 transfected 3Y1 cells compared with (b) cells transfected with empty vector. B. A functional network involving many of these upregulated (pink) and downregulated (green) genes. Functions include cell cycle, cellular assembly and organization, DNA replication, recombination and repair.

Figure 2

Expressional clustering based on 254 MUC1-CD-associated genes is associated with survival of lung adenocarcinoma patients. A. 3-dimensional representation of the centroids generated by K-means clustering. Each point forming a cloud surrounding the centroid represents a patient assigned to the cluster corresponding to the centroid. B. 5-year survival of patients assigned to each cluster.

Figure 3

ROC curves analyzing the use of expression levels of individual genes, CCNB1, CDC20 and CDKN3, to accurately assign patients to prognostic groups.

Figure 4

Expression of genes in the MUC1-Associated Proliferation Signature (MAPS). Survival and disease-free survival for expressors of the signature (MAPS+, n = 212) compared with non-expressors (MAPS-, n = 229).

Figure 5

Survival in all patients in the database in whom lymph node status is known. Survival is inferior in node-positive patients and in patients who are expressors (MAPS+). MAPS adds significantly to prognostication in both node-negative and node-positive patients.

Figure 6

Expressional clustering of genes in the MAPS signature in a second lung adenocarcinoma database. Survival for these groups is shown in a Kaplan-Meier curve with expressors (MAPS+, n = 52) and non-expressors (MAPS-, n = 32).