Urothelial cancer (UC) of the upper urinary tract (UUT) is relatively rare, and accounts for only 5% of all UC; however, its prognosis is very poor. For example, the 5-year survival rate of patients with pT4 or metastasis is only 10% . To improve survival and morbidity, numerous reports on the biological and pathological characteristics of this type of cancer have been published . However, more detailed and accurate information regarding its pathological features, biological markers for outcome, and potential therapeutic targets is warranted to improve follow-up and develop treatment strategies for patients with UC-UUT.
Angiogenesis plays a key role in various physiological and pathological processes . Additionally, angiogenesis is important in tumour growth, metastasis, and prognosis in many types of malignancies, including UC [3, 4]. Thrombospondin (TSP)-1 is a well-known potent inhibitor of angiogenesis in various physiological and pathological conditions, as it is capable of inhibiting proliferation, migration, and formation of tube-like structures in endothelial cells [5, 6]. These anti-angiogenic functions of TSP-1 are also present in various cancers . Conversely, it is thought that TSP-1 can also stimulate angiogenesis in cancer . Indeed, the pro-angiogenic effects of TSP-1 have been previously detected in several cancers including pancreatic cancer and gastric cancer [9, 10]. Thus, TSP-1 has opposing angiogenic functions that are dependent on the cancer type.
In recent years, many investigators have paid attention to lymph angiogenesis, as it has been proposed to play important roles in the dissemination of cancer cells and progression of various cancers similar to angiogenesis [11, 12]. Several reports demonstrated that TSP-1 is significantly associated with vascular endothelial growth factor (VEGF) function in various cancers [10, 13, 14]. Furthermore, VEGF was also reported to be associated with lymph angiogenesis in cancer tissues, including UC . Thus, while there is a possibility that TSP-1 is associated with lymph angiogenesis in patients with cancer, there is no information regarding this issue in human cancer tissues.
TSP-1 can also regulate the production of matrix metalloproteinase (MMP)-9 [15, 16]. MMP-9 is a type IV collagenase of the MMP family that is capable of cleaving a wide range of extracellular matrix components . In fact, increased MMP-9 levels have been reported to be closely associated with high stages of cancer in various human tissues, including UC-UUT [16, 18]. However, as with angiogenesis, TSP-1 appears to have dual roles in the regulation of MMP-9 function in cancer, that is, either as a stimulator [13, 15] or an inhibitor [19, 20]. In regards to TSP-1 and tumour growth, there are several reports suggesting that TSP-1 may inhibit cancer cell proliferation in several cancers [21, 22]. Despite this, TSP-1 was also previously reported to stimulate cell proliferation in colon cancer cells . Thus, TSP-1 is capable of acting as both a stimulator and inhibitor of cancer cell proliferation. It is well-known that TSP-1 can induce apoptosis in endothelial cells . Similarly, several investigators have found that TSP-1 induces apoptosis in malignant cells [24, 25]. However, other investigators reported that TSP-1 has anti-apoptotic effects in thyroid cancer . Thus, the direct function and pathological role of TSP-1 in regards to apoptosis of cancer cells is not still fully understood.
There is a wide range of opinions regarding the pathological role, clinical significance, and predictive value of TSP-1 in cancer patients. For example, there are several reports suggesting that low TSP-1 expression is correlated with increases in malignant aggressiveness and poorer outcomes in several cancers, including bladder cancer, prostate cancer, and renal cell carcinoma [14, 22, 27, 28]. Furthermore, high expression of TSP-1 has been associated with high grade, high stage, and poor prognosis in several cancers [13, 29, 30]. On the other hand, TSP-1 expression has not been associated with the clinicopathological features of renal cell carcinoma and advanced gastric cancer [10, 31]. Consequently, the roles of TSP-1 in the clinicopathological features, malignant aggressiveness, and prognosis of various cancers are extremely confusing. Further studies are necessary to reach a consensus on the pathological significance of TSP-1 in various cancers.
TSP-1 is a disulfide-bonded trimer with several different domains. Specifically, it consists of an N-terminal domain, a pro-collagen homology region, CSVTCG sequences within the type I repeats, a RGD sequence within the type 3 repeats, and a C-terminal domain . As mentioned previously, the regulation of TSP-1 function is complex, and involves direct and indirect effects. To clarify the detailed biological and pathological functions of TSP-1, various synthetic peptides derived from TSP-1, such as peptide from the type I repeats (i.e. KRFK and WSHSPW) and peptides from the N-terminal domain (i.e. GQGVLQNVRFVF), have been used [33, 34]. Interestingly, one report suggests that the 4N1K peptide (KRFYVVMWKK), which is derived from the C-terminal domain of TSP-1, inhibits angiogenesis both in in vivo and in vitro models . 4N1K expression was also reported to be negatively associated with angiogenesis in human renal cell carcinoma tissues . However, the clinical and pathological significance of the 4N1K peptide in urothelial cancer (UC) is still unknown.
In the present study, we paid close attention to the pathological role, clinical significance, and prognostic value of 4N1K expression in patients with UC of the upper urinary tract (UC-UUT), as this cancer is characterized by frequent recurrence after initial treatment. Angiogenesis, lymph-angiogenesis, proliferation, apoptosis, and MMP-9 are known to affect the malignant behaviour, tumour progression, and prognosis of UC-UUT [16, 18]. Thus, the main goal of the present study was to examine whether 4N1K expression correlates with malignant behaviour, clinicopathological features, and prognosis in patients with non-metastatic UC-UUT.