Abstract
BackgroundIdentifying cellular signaling pathways that become corrupted in the presence of androgens that increase the metastatic potential of organ-confined tumor cells is critical to devising strategies capable of attenuating the metastatic progression of hormone-naïve, organ-confined tumors. In localized prostate cancers, gene fusions that place ETS-family transcription factors under the control of androgens drive gene expression programs that increase the invasiveness of organ-confined tumor cells. C-X-C chemokine receptor type 4 (CXCR4) is a downstream target of ERG, whose upregulation in prostate-tumor cells contributes to their migration from the prostate gland. Recent evidence suggests that CXCR4-mediated proliferation and metastasis of tumor cells is regulated by CXCR7 through its scavenging of chemokine CXCL12. However, the role of androgens in regulating CXCR4-mediated motility with respect to CXCR7 function in prostate-cancer cells remains unclear.MethodsImmunocytochemistry, western blot, and affinity-purification analyses were used to study how androgens influenced the expression, subcellular localization, and function of CXCR7, CXCR4, and androgen receptor (AR) in LNCaP prostate-tumor cells. Moreover, luciferase assays and quantitative polymerase chain reaction (qPCR) were used to study how chemokines CXCL11 and CXCL12 regulate androgen-regulated genes (ARGs) in LNCaP prostate-tumor cells. Lastly, cell motility assays were carried out to determine how androgens influenced CXCR4-dependent motility through CXCL12.ResultsHere we show that, in the LNCaP prostate-tumor cell line, androgens coordinate the expression of CXCR4 and CXCR7, thereby promoting CXCL12/CXCR4-mediated cell motility. RNA interference experiments revealed functional interactions between AR and CXCR7 in these cells. Co-localization and affinity-purification experiments support a physical interaction between AR and CXCR7 in LNCaP cells. Unexpectedly, CXCR7 resided in the nuclear compartment and modulated AR-mediated transcription. Moreover, androgen-mediated cell motility correlated positively with the co-localization of CXCR4 and CXCR7 receptors, suggesting that cell migration may be linked to functional CXCR4/CXCR7 heterodimers. Lastly, CXCL12-mediated cell motility was CXCR7-dependent, with CXCR7 expression required for optimal expression of CXCR4 protein.ConclusionsOverall, our results suggest that inhibition of CXCR7 function might decrease the metastatic potential of organ-confined prostate cancers.Electronic supplementary materialThe online version of this article (doi:10.1186/s12885-015-1201-5) contains supplementary material, which is available to authorized users.
Highlights
Identifying cellular signaling pathways that become corrupted in the presence of androgens that increase the metastatic potential of organ-confined tumor cells is critical to devising strategies capable of attenuating the metastatic progression of hormone-naïve, organ-confined tumors
C-X-C chemokine receptor type 7 (CXCR7) is a key regulator of C-X-C chemokine receptor type 4 (CXCR4)-dependent motility [17,18,37,38,39], and we have previously shown that it is an androgen-sensitive microsomal protein in the LNCaP prostate-cancer cell line [40]
PAbCXCR7 immunoreactivity was specific for CXCR7, as immunoreactive bands were competitively removed when pAbCXCR7 was preincubated with the C-terminal CXCR7 peptide, but not with the non-competitive androgen receptor (AR) peptide (Figure 1A, right panel versus left panel)
Summary
Identifying cellular signaling pathways that become corrupted in the presence of androgens that increase the metastatic potential of organ-confined tumor cells is critical to devising strategies capable of attenuating the metastatic progression of hormone-naïve, organ-confined tumors. The role of androgens in regulating CXCR4-mediated motility with respect to CXCR7 function in prostate-cancer cells remains unclear. Given that current therapies are ineffective at curing these more advanced cancers, it has become common to treat patients at the organ-confined stage of disease. This results in the significant overtreatment of lowrisk, organ-confined prostate cancer, as the majority of the early-stage tumors are indolent [2]. Identifying biomarkers linked to the metastasis of prostate tumor cells will be critical to distinguish tumors with a high risk of progression from those that are truly indolent
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