HuR Involvement in PTHrP Expression in Human Lung Adenocarcinoma.
Libero Lauriola, Giovanni Monego, Paola Lanza, Mariangela Novello, Franco Oreste Ranelletti. Catholic University, Rome, Italy
Background: PTHrP posses growth factor-like properties and is involved in the growth and invasion of multiple cancers. We have previously shown that, in lung adenocarcinoma, both PTHrP and cytoplasmic HuR expressions are correlated with a worse clinical outcome. Recently, it has been reported that, in renal cell carcinoma, HuR is involved in PTHrP upregulation, so we studied 54 lung adenocarcinomas, to ascertain whether HuR is involved in the regulation of PTHrP expression.
Design: Immunohistochemical analysis was performed on neoplastic tissue from 54 lung adenocarcinomas, with anti-HuR and anti-PTHrP antibodies. In order to further investigate the role of HuR, in vitro studies were performed on HCC44 human lung adenocarcinoma cell line, by siRNA transfection.
Results: Double immunohistochemical staining revealed that HuR and PTHrP are co-expressed in tumor cells. Moreover, by quantitative immunohistochemistry, we found that the expression of HuR (measured as nuclear/cytoplasmic ratio: N/C) and that of PTHrP are inversely correlated. With a median follow-up of 36 months (range 3-194), metastases occurred in 19 out of 54 cases and 12 out of 54 patients had died of cancer. Cox's regression analysis, using PTHrP as continous covariate, showed that PTHrP levels were directly associated with the risk of death and metastases. We further evaluated whether the adjustement for HuR N/C status of the tumors added information to the relationship between PTHrP levels and the metastases-free and overall survival rates. Plots of the Cox's model estimates of the overall and metastasis-free survival as a function of PTHrP levels, for patients with HuR N/C high or low tumors, showed that, at 5-year follow-up, the estimated proportions of metastasis-free surviving patients, at the mean value of PTHrP, were 90.1% and 70.2% for those with tumors displaying high and low HuR N/C, respectively. Relative to the overall survival, the estimated proportions of surviving patients were 92.5% and 55.0% for those with tumors displaying high and low HuR N/C, respectively. In HCC44 human adenocarcinoma cell line, knockdown of HuR expression by siRNA tranfection reduced cell growth and this effect was partially prevented by addition of exogenous PTHrP; immunocytochemical and western blot analyses revealed that knockdown of HuR reduced the levels of PTHrP.
Conclusions: These observations suggest that in human lung adenocarcinoma the expression of PTHrP is regulated by the RNA-binding protein HuR, adding further interest on HuR, also as a molecular target for tumor therapy.
Tuesday, March 1, 2011 1:00 PM
Poster Session IV # 249, Tuesday Afternoon