Clinical significance of NGAL mRNA expression in human rectal cancer

Background: Emerging evidence has demonstrated that Neutrophil gelatinase-associated lipocalin (NGAL) is up-regulated in multiple malignancies, including oesophagus cancer, and plays a critical role in tumorigenesis and progression.However,till now, little is known about the role of NGAL in human rectal cancer. Its association with clinicopathologic characteristics and expression of MMP-9, one of its target genes, has not been reported systematically in rectal cancer. Therefore,to further determine the potential involvement of NGAL in rectal cancer, we have evaluated the expression level of NGAL mRNA by real time RT-PCR, and further elucidated the correlation of NGAL mRNA expression with clinicopathologic features and MMP-9 in rectal cancer. Methods: 100 paired samples of rectal cancer and adjacent normal tissues obtained from inpatients undergoing surgical operation were allocated into two groups (cancer group and control group).The mRNA expression of NGAL and MMP-9 was determined by real-time RT-PCR. The association between their expression and clinicopathological characteristics of rectal cancer were analysised. Results: Among the 100 rectal cancers, 69 cases of NGAL mRNA up-regulation were observed. NGAL mRNA up-regulation was positively correlated with MMP-9(rs=0.393,p<0.001). In rectal cancer, NGAL mRNA overexpression was associated significantly with depth of invasion(p=0.028),lymph node metastasis(p=0.009), venous involvement(p=0.023) and advanced pTNM stage(p=0.011). Conclusions: In human rectal cancer,NGAL mRNA expression was elevated.NGAL mRNA up-regulation was correlated significantly with tumor progression and MMP-9 mRNA overexpression in rectal cancer, suggesting a more aggressive phenotype. NGAL could be used for rectal cancer characterization. f Background Colorectal cancer(CRC) is one of the common gastrointestinal cancers worldwide and the second leading cause of cancer-related deaths in Europe.[1]In the United States, colorectal cancer was the third most common cause of cancer related death in 2007[2]. About 30% to 60% of patients with colorectal cancer undergoing primary surgery with curative intention still die from metastatic disease[3].Compared to colon cancer, rectal cancer, with worse prognosis, is mainly attributed to higher advanced cancer resulting from progression and metastasis of the tumor, which are two of the most important factors in determining the prognosis of patients with rectal cancers[4].The early diagnosis of rectal cancer is difficult owing to the late presentation of symptom. The scarcity of early biomarkers has considerably hindered our ability to launch preventive measures for this malignancy in a timely manner. So it is important to find superior tumor markers implicated in the progression and metastasis of rectal cancer. NGAL,a 24-kDa glycoprotein,also known as lipocalin-2, belongs to the lipocalin protein family.The rat NGAL homologue, neu-related lipocalin(NRL), was first identified as a gene whose expression was specifically induced in HER-2/neu oncogene-induced rat mammary carcinomas[5]. NGAL exists as monomer (25 kDa), homodimer(46 kDa), and disulfide-linked heterodimer with Matrix Metalloproteinase-9 (MMP-9,135 kDa)[6, 7].As a member of the MMP family, MMP-9 has been implicated to cancer progression by degradation of the molecular components of the basement membrane and extracellular matrix, liberating vascular endothelial cell growth factor (VEGF) from the extracellular matrix and therefore enabling angiogenesis, invasion and distant metastasis[8-10]. Growing evidence has demonstrated that NGAL can form a complex with MMP-9 and improves MMP-9 expression, prevents its degradation, causing increased MMP-9 enzymatic activity, thereby favoring invasive and metastatic potential of cancer cells in vivo and in vitro[11-13]. Elevated NGAL expression has also been detected in a variety of malignancies and involved in the invasion and progression of tumors, including breast cancer, esophageal carcinoma and gastric cancer et al[13-15]. Up to now, however, little is known about the role of NGAL in human rectal cancer. Its association with clinicopathologic characteristics and expression of MMP-9, one of its target genes, in rectal cancer has not been reported systematically. Therefore,to further determine the potential involvement of NGAL in rectal cancer, we detected mRNA expression of NGAL and MMP-9 in matched rectal samples by real time RT-PCR, and further evaluated the correlation between NGAL and MMP-9 as well as clinicopathological features in human rectal cancer.