Low expression of the putative tumour suppressor spinophilin is associated with higher proliferative activity and poor prognosis in patients with hepatocellular carcinoma

Background: Spinophilin, a multifunctional intracellular scaffold protein, is reduced in certain types of cancer and is regarded as a novel putative tumour suppressor protein. However, the role of spinophilin in hepatocellular carcinoma (HCC) has never been explored before. Methods: In this study, we determined for the first time the expression pattern of spinophilin in human HCC by immunohistochemistry and quantitative reverse transcriptase–PCR analysis. In addition, we performed immunohistochemical analysis of p53, p14 ARF and the proliferation marker Ki-67. Kaplan–Meier curves and multivariate Cox proportional models were used to study the impact on clinical outcome. Small interfering RNA (siRNA) was used to silence spinophilin and to explore the effects of reduced spinophilin expression on cellular growth. Results: In our study, complete loss of spinophilin immunoreactivity was found in 44 of 104 HCCs (42.3%) and reduced levels were found in an additional 37 (35.6%) cases. After adjusting for other prognostic factors, multivariate Cox regression analysis identified low expression of spinophilin as an independent prognostic factor with respect to disease-free (hazard ratio (HR)=1.8; 95% confidence interval (CI)=1.04–3.40; P =0.043) and cancer-specific survival (HR=2.0; CI=1.1–3.8; P =0.025). Reduced spinophilin expression significantly correlated with higher Ki-67 index in HCC ( P =0.014). Reducing spinophilin levels by siRNA induced a higher cellular growth rate and increased cyclin D2 expression in tumour cells ( P