Abstract 2451: CD133+ liver tumor-initiating cells promote tumor growth, angiogenesis and self-renewal through activation of the neurotensin / interleukin-8 signaling cascade

Abstract

Abstract A novel paradigm in tumor biology suggests that cancer growth is driven by stem-like cells within a tumor, called tumor-initiating cells (TICs). We have previously identified a TIC population from hepatocellular carcinoma (HCC) that is marked by a CD133 surface phenotype and bears features that include the abilities to self-renew, differentiate, initiate tumors in vivo and resist standard chemotherapy through AKT pathway dysregulation (Ma et al., Gastroenterology 2007; Oncogene 2008 and Cell Stem Cell in press). Our present study aims to investigate the underlying molecular mechanism by which CD133+ liver TICs mediate tumor growth and maintenance. cDNA microarray approach was employed to compare gene expression profiles between sorted CD133 subpopulations in HCC cell lines Huh7 and PLC8024. A dysregulated interleukin-8 (IL-8) signaling functional network was preferentially identified in CD133+ liver TICs. IL-8 was found to be overexpressed at both genomic and proteomic (endogenous and secretory) levels in CD133+ cells isolated from HCC cell lines and clinical samples; while its expression also correlated positively with CD133 expression in a panel of liver cell lines. Functional studies on sorted CD133 HCC cells found enhanced IL-8 secretion in CD133+ liver TICs to possess a greater ability to self-renew and induce tumor angiogenesis and growth in vitro and in vivo. These observations were further validated when silencing of IL-8 in CD133+ liver TICs by knockdown or neutralizing antibody approach led to abolishment of these effects. Subsequent studies in the IL-8 functional network also found neurotensin (NTS) and chemokine ligand 1 (CXCL1) to be preferentially expressed in CD133+ liver TICs. Their expression also correlated with that of CD133 and IL-8 across a panel of liver cell lines. Upon addition of exogenous NTS, both expression of IL-8 and CXCL1 was dramatically up-regulated, with concomitant activation of phospho-ERK1/2, a key player of the mitogen-activated protein kinase (MAPK) signaling pathway. Interestingly, enhanced IL-8 secretion in CD133+ liver TICs can in turn activate an IL-8 positive feedback loop through MAPK signaling. Lastly, we also provide evidence to show that the transmembrane protein, CD133, apart from serving as a liver TIC marker, also plays a critical functional role in conferring TIC properties. Stable repression of CD133 in CD133+ liver TICs by lentiviral based approach resulted in inactivation of the NTS / IL-8 / CXCL1 / MAPK signaling cascade and attenuation of TIC self-renewal and tumorigenic properties. Taken together, these results suggest that CD133+ liver TICs promote tumor growth, angiogenesis and self-renewal through activation of NTS / IL-8 signaling cascade. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2451. doi:10.1158/1538-7445.AM2011-2451