Expression of cyclin D1 splice variants is differentially associated with outcome in non-small cell lung cancer patients

Abstract

Real-time reverse transcription polymerase chain reaction and immunohistochemistry were used to evaluate the messenger RNA (mRNA) and protein expression levels of total cyclin D1 and its splice variants (cyclin D1a and cyclin D1b) in 102 paired malignant and nonmalignant tissues from patients with non-small cell lung cancer, respectively. The expression levels of total cyclin D1 and its splice variants were significantly up-regulated in malignant tissues than in nonmalignant tissues at both mRNA and protein levels. Although the expression levels of cyclin D1a were higher than those of cyclin D1b, the relative expression ratios of cyclin D1b mRNA between malignant and nonmalignant lung tissues were obviously higher than those of cyclin D1a mRNA. Analysis of variance showed that cyclin D1b mRNA expression was significantly associated with the histologic grade, lymph node metastasis, distant metastasis, and tumor stage of patients, whereas cyclin D1a mRNA expression was not related to clinicopathologic characteristics except sex. Patients with cyclin D1b mRNA expression above the median value had shorter survival than those below the median value (P = .033). Similarly, cyclin D1b immunopositivity was also associated with histologic grade, and patients with immunostaining positivity for cyclin D1b showed poor survival (P = .005). Multivariate analysis demonstrated that cyclin D1b immunopositivity was an independent risk factor in survival of patients with non-small cell lung cancer (P = .018). Our data show that cyclin D1b, rather than canonical cyclin D1a, might contribute to the development of non-small cell lung cancer. Cyclin D1b would be a better prognostic indicator for non-small cell lung cancer as compared to total cyclin D1 or cyclin D1a.