Upregulation of SOX9 in lung adenocarcinoma and its involvement in the regulation of cell growth and tumorigenicity

[[abstract]]PURPOSE: SOX9 is an important transcription factor required for development and has been implicated in several types of cancer. However, SOX9 has never been linked to lung cancer to date. Here we demonstrate that SOX9 expression is upregulated in lung adenocarcinoma and show how it is associated with cancer cell growth.EXPERIMENTAL DESIGN: Data mining with 5 microarray datasets containing 490 clinical samples, qRT-PCR validation assay in 57 independent samples, and immunohistochemistry assay with tissue microarrays containing 170 lung tissue cores, were used to profile SOX9 mRNA and protein expression. siRNA suppression of SOX9 in cell lines was used to scrutinize functional role(s) of SOX9 and associated molecular mechanisms.RESULTS: SOX9 mRNA and protein were consistently overexpressed in the majority of lung adenocarcinoma. Knockdown of SOX9 in lung adenocarcinoma cell lines resulted in marked decrease of adhesive and anchorage-independent growth in concordance with upregulation of p21 (CDKN1A) and downregulation of CDK4. In agreement with higher SOX9 expression level in lung adenocarcinoma, the p21 mRNA level was significantly lower in tumors than that in normal tissues, while the opposite was true for CDK4, supporting the notion that SOX9 negatively and positively regulated p21 and CDK4 respectively. Finally, while SOX9-knockdown cells showed significantly attenuated tumorigenicity in mice, SOX9 transfectants consistently showed markedly stronger tumorigenicity.CONCLUSIONS: Our data suggest SOX9 is a new hallmark of lung adenocarcinoma, in which SOX9 might contribute to gain of tumor growth potential, possibly acting through affecting the expression of cell cycle regulators p21 and CDK4