Identification of Galanin and Its Receptor GalR1 as Novel Determinants of Resistance to Chemotherapy and Potential Biomarkers in Colorectal Cancer

Abstract

Purpose: A major factor limiting the effective clinical management of colorectal cancer (CRC) is resistance to chemotherapy. Therefore, the identification of novel, therapeutically targetable mediators of resistance is vital.Experimental design: We used a CRC disease-focused microarray platform to transcriptionally profile chemotherapy-responsive and nonresponsive pretreatment metastatic CRC liver biopsies and in vitro samples, both sensitive and resistant to clinically relevant chemotherapeutic drugs (5-FU and oxaliplatin). Pathway and gene set enrichment analyses identified candidate genes within key pathways mediating drug resistance. Functional RNAi screening identified regulators of drug resistance.Results: Mitogen-activated protein kinase signaling, focal adhesion, cell cycle, insulin signaling, and apoptosis were identified as key pathways involved in mediating drug resistance. The G-protein-coupled receptor galanin receptor 1 (GalR1) was identified as a novel regulator of drug resistance. Notably, silencing either GalR1 or its ligand galanin induced apoptosis in drug-sensitive and resistant cell lines and synergistically enhanced the effects of chemotherapy. Mechanistically, GalR1/galanin silencing resulted in downregulation of the endogenous caspase-8 inhibitor FLIP L , resulting in induction of caspase-8-dependent apoptosis. Galanin mRNA was found to be overexpressed in colorectal tumors, and importantly, high galanin expression correlated with poor disease-free survival of patients with early-stage CRC.Conclusion: This study shows the power of systems biology approaches to identify key pathways and genes that are functionally involved in mediating chemotherapy resistance. Moreover, we have identified a novel role for the GalR1/galanin receptor-ligand axis in chemoresistance, providing evidence to support its further evaluation as a potential therapeutic target and biomarker in CRC.

Physiology, Signaling, and Pharmacology of Galanin Peptides and Receptors: Three Decades of Emerging Diversity

“…Interestingly, the majority of these tumors exhibited significantly higher galanin levels than corresponding noncancerous tissue (Skotheim et al, 2005;Gilaberte et al, 2007;Kim et al, 2007;Sugimoto et al, 2009;Stevenson et al, 2012), similar to observations of human pheochromocytoma (Bauer et al, 1986c). In colon cancers, GAL mRNA levels were observed to increase significantly with tumor size and stage (Kim et al, 2007), and a recent study found a significant correlation between high galanin expression and poorer disease-free survival in colon cancer patients, identifying galanin as a potential biomarker for certain cancer types (Stevenson et al, 2012).…”

“…Increased GAL 1 expression was also observed in human pituitary adenomas relative to levels in normal human pituitaries (Tofighi et al, 2012), suggesting cancer-promoting properties for GAL 1 , at least in these tumors. Recently, GAL 1 was proposed to contribute to resistance to chemotherapeutic drugs in colon cancer, because GAL 1 silencing led to enhanced chemosensitivity of human colon cancer cell lines (Stevenson et al, 2012). This is somewhat contrary to the finding that advanced colorectal carcinomas often display chromosomal alterations with a loss of the GAL 1 locus on 18q (Knosel et al, 2002).…”

“…Indeed, a correlation between the amount of galanin in neuroblastoma and their differentiation status was reported (Perel et al, 2002), although a similar study could not confirm this correlation (Berger et al, 2002) Galanin was also detected in a variety of nonneuroendocrine human tumors of different origin, including glioblastoma and other brain tumors (Berger et al, 2003), melanoma (Gilaberte et al, 2007), head and neck squamous cell carcinoma (HNSCC) (Sugimoto et al, 2009), basal cell carcinoma (Kepron et al, 2009), colon cancer (Kim et al, 2007;Godlewski and Pidsudko, 2012;Stevenson et al, 2012), and embryonic carcinoma (Skotheim et al, 2005). Interestingly, the majority of these tumors exhibited significantly higher galanin levels than corresponding noncancerous tissue (Skotheim et al, 2005;Gilaberte et al, 2007;Kim et al, 2007;Sugimoto et al, 2009;Stevenson et al, 2012), similar to observations of human pheochromocytoma (Bauer et al, 1986c). In colon cancers, GAL mRNA levels were observed to increase significantly with tumor size and stage (Kim et al, 2007), and a recent study found a significant correlation between high galanin expression and poorer disease-free survival in colon cancer patients, identifying galanin as a potential biomarker for certain cancer types (Stevenson et al, 2012).…”

“…Initially, galanin receptors were identified in a hamster pancreatic cell tumor and a rat insulinoma cell line (Amiranoff et al, 1987;LagnyPourmir et al, 1989). In humans, galanin receptors were first discovered in pituitary tumors (Hulting et al, 1993) and were subsequently identified in pheochromocytoma , neuroblastoma (Tuechler et al, 1998), glioma (Berger et al, 2003), prostate carcinoma , colon carcinoma (Stevenson et al, 2012), HNSCC (Misawa et al, 2008), and SCLC cell lines (Wittau et al, 2000).…”

Myenteric plexuses atrophy in the vicinity of colorectal cancer tissue is not caused by apoptosis or necrosis

“…In an in vitro study it was shown that GAL or type 1 G protein-coupled receptor galanin receptor (GALR1) silencing induced apoptosis in drug-sensitive and drug-resistant CRC cell lines. GALR1 silencing caused down-regulation of FLIP1, an endogenous CASP8 inhibitor, and consequently affected the activation of external pathway of apoptosis [16]. This putative apoptosis-protective role of galanin could represent another, as yet unrecognized, aspect of the neuroprotective function of this neuropeptide.…”