Serum CXCL13 positively correlates with prostatic disease, prostate-specific antigen and mediates prostate cancer cell invasion, integrin clustering and cell adhesion
Introduction
PCa is one of the leading causes of cancer-related deaths among men in US [1]. Despite recent advancements in early diagnosis (e.g., PSA monitoring and digital rectal examination) and treatment, metastasis is still a major cause of mortality in PCa [2]. Unfortunately, the mechanisms involved in the malignant process are not completely understood [3], [4] and PSA cannot be used to solely predict the extent of prostatic disease [5]. Introduction of PSA as a screening tool has had a dual effect – dramatically decreasing the incidence of advanced PCa and increasing the number of new cases of PCa [6]. However, men with normal levels of total serum PSA can have PCa. Indeed, 15% of PCa cases with positive biopsies had PSA levels <4 ng/mL and a weak association of PSA with tumor volume [5], [7]. Taken together, these studies demonstrate the great need for additional biomarkers to improve or complement the use of PSA that might also correlate with advanced disease.
Bone metastases are frequent complications of many cancers and occur in up to 70% of patients with advanced PCa [8]. The exact incidence of bone metastasis is unknown, but it is estimated that 350,000 people diagnosed with cancer die with bone (osteolytic or osteoblastic) metastases annually in the US [9]. PCa lesions are predominantly osteoblastic [10]. Tumor cells produce adhesive molecules that allow them to bind bone marrow (i.e., stromal cells, bone matrix proteins, etc.). These adhesive interactions cause tumor cells to colonize in this environment as well as increase the production of angiogenic and bone-resorbing factors for enhanced tumor growth. In this regard, studies from our laboratory and others indicate that multiple chemokines and their corresponding receptors (including CCR5, CCR7, CCR9, CXCR3, CXCR4, CXCR5, and CXCR7) may be involved in the multi-step and dynamic process of PCa cell metastasis [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22]. In this study, we show that CXCL13 and IL-6 is highly elevated in PCa patient sera and positively correlated with serum PSA. Surprisingly, serum CXCL13 levels seem to be a better predictor of advanced disease than PSA. We also show that HBME cells and OBs secrete CXCL13 after IL-6 stimulation, which is known to be highly elevated in the sera of patients with metastatic disease [23]. Lastly, we demonstrate that the CXCR5 axis is involved in αvβ3 integrin clustering for adhesion of PCa cells to HBME cells.
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Cell lines and cell culture
PC3 cell lines were obtained from ATCC, Dr. Kenneth Pienta (University of Michigan) provided HBME cells, human OB and OC cell lines were obtained from Clonetics. PC3 cell lines were cultured in Ham’s F12 K medium with 2 mM l-glutamine and adjusted to contain 1.5 g/L sodium bicarbonate (ATCC) with 10% fetal bovine serum (FBS) (Sigma). After five passages in Ham’s F12 K media, PC3 cells were switched to RPMI-1640 with 10% fetal bovine serum FBS. HBME cells were cultured in Dulbecco’s Modified Eagle
Serum CXCL13, PSA, and cytokine levels in subjects with prostatic disease or healthy donors
Serum CXCL13 was significantly (p < 0.001) higher in PCa patients compared to patients with HGPIN or BPH and NHD (Fig. 1). As expected, total PSA levels in PCa patient serum was significantly higher (p < 0.001) than compared to HGPIN, BPH, and NHD subjects (Fig. 1B). Interestingly, CXCL13 serum levels seemed to provide a better distinction among PCa, BPH, HGPIN, or NHD subjects than PSA (Fig. 2A). All PCa patients had serum CXCL13 levels >75 pg/mL, which clearly differentiated PCa from other cases
Discussion
Despite recent advances in the treatment and diagnosis of cancer, PCa remains the second leading cause of cancer-related deaths among men in US. Detecting PCa at earlier curable stages has been facilitated by the measurement of the PSA in serum [32]. The American Urological Society, the American Cancer Society, and the American College of Physicians recommend that PCa screening to be discussed with all men over 50 years of age, as well as men over the age of 40 with additional risk factors such
Conflicts of interest
None declared.
Acknowledgments
The content of this manuscript benefited from many fruitful conversations with members of the Morehouse School of Medicine, University of Alabama at Birmingham, Emory University, and the University of Louisville. This work benefited from the cooperation between investigators from the Morehouse School of Medicine and the Wallace Tumor Institute at the University of Alabama at Birmingham via the National Cancer Institute sponsored “Comprehensive Minority Institution/Cancer Center Partnership”.
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