Pathogenesis Of Prostatic Small Cell Carcinoma Involves The Inactivation Of The P53Pathway

Background:Prostate cancer (PC) is the most common malignancy in men and thesecond leading cause of cancer-related deaths，Although the majority of patients withadvanced prostate cancer have an initial response to androgen deprivation therapy(ADT)，nearly all patients will eventually progress to a ’castration-resistant’ state.Small cell neuroendocrine carcinoma (SCNC) of the prostate is a variant form ofprostate cancer that occurs de novo or as a recurrent tumor in patients who receivedhormonal therapy for prostatic adenocarcinoma. It is composed of pure neuroendocrine(NE) tumor cells，but unlike the scattered NE cells in benign prostate andadenocarcinoma that are quiescent, the NE cells in SCNC are highly proliferative andaggressive, causing death in months. While P53appears to be wildtype in the NE cellsof benign prostate and adenocarcinoma, immunohistochemical studies show that themajority of the NE tumor cells in SCNC are positive for nuclear p53，suggesting that thep53is mutated. In this study,we provide evidence to support the hypothesis that p53mutation leads to inactivation of the IL8-CXCR2-p53signaling pathway, resulting inthe loss of an important growth inhibitory mechanism and the hyper-proliferation of NEcells in SCNC.Methods:1. we transfected LNCaP cells with pcDNA3-CXCR2plasmid to EstablishLNCaP cell lines stably expressing IL8receptor CXCR2,2. We performed cell proliferation assay of LNCaP and LNCaP/CXCR2cells andexamined their proliferative responses to IL8. We also performed RNA isolation andMicroarray hybridization to examin the transcriptional responses to IL8by comparing thetranscriptional proifles of cells with or without IL8treatment. 3.We used a transient transfection method to introduce siRNA to reduce theendogenous P53level in LNCaP/CXCR2cells to determine whether a loss of P53activity would change the growth response toward IL8treatment.4.Tissue microarrays were constructed from Three hundred cases of prostatectomySpecimens, then, we performed immunohistochemistry to observe p53nuclear stainingin NE cells of benign prostate, prostatic adenocarcinoma, and SCNC. we usedimmunohistochemistry to study p53expression in31cases of prostatic SCNC usingregular histological sections, ifnally, we obtained formalin-ifxed, paraiffn-embeddedtissue from seven cases of prostatic SCNC and extracted genomic DNA from them.Exons5-10of p53were amplified by PCR followed by direct sequencing.Result:1. LNCaP/CXCR2cell lines stably expressing IL8receptor CXCR2. asconifrmed by immunoblot as well as lfow cytometric analysis with antibodies againstCXCR2.2.IL8inhibited the proliferation of LNCaP/CXCR2cells but not the parental LNCaPcells，Functional gene family analysis showed that among the genes whose expressionincreased signiifcantly in response to IL8stimulation were those controlling the Gl/Sand G2/M transition check points. As an important function of p53is in the cell cyclecontrol and growth inhibition,3.IL8treatment of the cells with reduced P53levels resulted in an increase in cellnumber while the control cells showed reduced cell numbers in response to IL8treatment,4.results of immunohistochemical staining and Genomic sequencing of p53exonssuggest that most, if not all, prostatic SCNCs contain mutations in the p53gene.Conclusion: a p53mutation inactivates the IL8-CXCR2-p53pathway that normallykeeps the NE cells in a quiescent state, resulting in hyper-proliferation and aggressivebehavior, features that are characteristic of the tumor cells in SCNC.