17beta-estradiol promotes breast cancer cell proliferation-inducing stromal cell-derived factor-1-mediated epidermal growth factor receptor transactivation: reversal by gefitinib pretreatment

Induction of Kruppel-like factor 5 expression by androgens results in increased CXCR4-dependent migration of prostate cancer cells in vitro

Advanced prostate cancers preferentially metastasize to bone, suggesting that this tissue produces factors that provide a suitable microenvironment for prostate cancer cells. Recently, it has become clear that even in antiandrogen-resistant cancers, the androgen receptor (AR)-signaling axis is required for prostate cancer progression. Therefore, we hypothesized that AR may be involved in the regulation of pathways that are responsible for the homing of prostate cancer cells to select microenvironments. In support of this hypothesis, we have determined that chemokine (C-X-C motif) receptor 4 (CXCR4), the receptor for the chemokine CXCL12, is up-regulated in prostate cancer cells in response to androgens. Given that the levels of CXCL12 are elevated at sites of known prostate cancer metastases such as bone, these results suggest that androgens may influence prostate cancer metastasis. Specifically, we demonstrate that androgens increase the levels of both CXCR4 mRNA and functional protein in LNCaP prostate cancer cells. Importantly, androgens enhanced the migration of LNCaP cells toward a CXCL12 gradient, an effect that could be blocked by the specific CXCR4 antagonist AMD3100. Interestingly, CXCR4 is not directly regulated by androgens but rather is positively up-regulated by Krüppel-like factor 5 (KLF5), a transcription factor that we have shown to be an early, direct target of AR. Further, KLF5 is both required and sufficient for androgen-mediated CXCR4 expression and migration toward CXCL12. Taken together, these findings demonstrate that AR can utilize the CXCL12/CXCR4 axis through induction of KLF5 expression to promote prostate cancer progression and highlight the potential utility of CXCR4 antagonists as prostate cancer therapeutics.

AMD3100 is a CXCR7 ligand with allosteric agonist properties

The bicyclam AMD3100 is known as a small synthetic inhibitor of the CXCL12-binding chemokine receptor CXCR4. Here, we show that AMD3100 also binds to the alternative CXCL12 receptor CXCR7. CXCL12 or AMD3100 alone activate beta-arrestin recruitment to CXCR7, which we identify as a previously unreported signaling pathway of CXCR7. In addition, AMD3100 increases CXCL12 binding to CXCR7 and CXCL12-induced conformational rearrangements in the receptor dimer as measured by bioluminescence resonance energy transfer. Moreover, small but reproducible increases in the potency of CXCL12-induced arrestin recruitment to CXCR7 by AMD3100 are observed. Taken together, our data suggest that AMD3100 is an allosteric agonist of CXCR7. The finding that AMD3100 not only binds CXCR4, but also to CXCR7, with opposite effects on the two receptors, calls for caution in the use of the compound as a tool to dissect CXCL12 effects on the respective receptors in vitro and in vivo.

Trastuzumab-induced HER reprogramming in "resistant" breast carcinoma cells

Although trastuzumab (Herceptin) is an important advance in the treatment of breast cancer, a significant proportion of patients do not respond to trastuzumab either alone or in combination with chemotherapy. In this study, we observe that epidermal growth factor receptor (EGFR) and HER3 expression is substantially increased after long-term trastuzumab exposure of HER2-positive breast carcinoma-derived cell lines that show primary resistance to trastuzumab. Furthermore, long-term trastuzumab exposure of trastuzumab-resistant cell lines induces de novo sensitivity to the EGFR-targeted agents gefitinib or cetuximab in two of three cell lines accompanied by increased EGFR expression. Together, these results indicate that primary trastuzumab resistance is not synonymous with lack of responsiveness to trastuzumab and, importantly, suggest that trastuzumab priming may sensitize trastuzumab-resistant tumors to other HER family-directed therapeutics.

Different response of human glioma tumor-initiating cells to epidermal growth factor receptor kinase inhibitors

Because a subpopulation of cancer stem cells (tumor-initiating cells, TICs) is believed to be responsible for the development, progression, and recurrence of many tumors, we evaluated the in vitro sensitivity of human glioma TICs to epidermal growth factor receptor (EGFR) kinase inhibitors (erlotinib and gefitinib) and possible molecular determinants for their effects. Cells isolated from seven glioblastomas (GBM 1-7) and grown using neural stem cell permissive conditions were characterized for in vivo tumorigenicity, expression of tumor stem cell markers (CD133, nestin), and multilineage differentiation properties, confirming that these cultures are enriched in TICs. TIC cultures were challenged with increasing concentrations of erlotinib and gefitinib, and their survival was evaluated after 1-4 days. In most cases, a time- and concentration-dependent cell death was observed, although GBM 2 was completely insensitive to both drugs, and GBM 7 was responsive only to the highest concentrations tested. Using a radioligand binding assay, we show that all GBM TICs express EGFR. Erlotinib and gefitinib inhibited EGFR and ERK1/2 phosphorylation/activation in all GBMs, irrespective of the antiproliferative response observed. However, under basal conditions GBM 2 showed a high Akt phosphorylation that was completely insensitive to both drugs, whereas GBM 7 was completely insensitive to gefitinib, and Akt inactivation occurred only for the highest erlotinib concentration tested, showing a precise relationship with the antiproliferative effects of the drug. Interestingly, in GBM 2, phosphatase and tensin homolog expression was significantly down-regulated, possibly accounting for the insensitivity to the drugs. In conclusion, glioma TICs are responsive to anti-EGFR drugs, but phosphatase and tensin homolog expression and Akt inhibition seem to be necessary for such effect.

Signal integration: a framework for understanding the efficacy of therapeutics targeting the human EGFR family

The human EGFR (HER) family is essential for communication between many epithelial cancer cell types and the tumor microenvironment. Therapeutics targeting the HER family have demonstrated clinical success in the treatment of diverse epithelial cancers. Here we propose that the success of HER family-targeted monoclonal antibodies in cancer results from their ability to interfere with HER family consolidation of signals initiated by a multitude of other receptor systems. Ligand/receptor systems that initiate these signals include cytokine receptors, chemokine receptors, TLRs, GPCRs, and integrins. We further extrapolate that improvements in cancer therapeutics targeting the HER family are likely to incorporate mechanisms that block or reverse stromal support of malignant progression by isolating the HER family from autocrine and stromal influences.

Overexpression of stromal cell-derived factor 1 and its receptor CXCR4 induces autocrine/paracrine cell proliferation in human pituitary adenomas

PURPOSE

Hypothalamic or locally produced growth factors and cytokines control pituitary development, functioning, and cell division. We evaluated the expression of the chemokine stromal cell-derived factor 1 (SDF1) and its receptor CXCR4 in human pituitary adenomas and normal pituitary tissues and their role in cell proliferation.

EXPERIMENTAL DESIGN

The expression of SDF1 and CXCR4 in 65 human pituitary adenomas and 4 human normal pituitaries was determined by reverse transcription-PCR, immunohistochemistry, and confocal immunofluorescence. The proliferative effect of SDF1 was evaluated in eight fibroblast-free human pituitary adenoma cell cultures.

RESULTS

CXCR4 mRNA was expressed in 92% of growth hormone (GH)-secreting pituitary adenomas (GHoma) and 81% of nonfunctioning pituitary adenomas (NFPA), whereas SDF1 was identified in 63% and 78% of GHomas and NFPAs, respectively. Immunostaining for CXCR4 and SDF1 showed a strong homogenous labeling in all tumoral cells in both GHomas and NFPAs. In normal tissues, CXCR4 and SDF1 were expressed only in a subset of anterior pituitary cells, with a lower expression of SDF1 compared with its cognate receptor. CXCR4 and SDF1 were not confined to a specific cell population in the anterior pituitary but colocalized with discrete subpopulations of GH-, prolactin-, and adrenocorticorticotropic hormone-secreting cells. Conversely, most of the SDF1-containing cells expressed CXCR4. In six of eight pituitary adenoma primary cultures, SDF1 induced a statistically significant increase in DNA synthesis that was prevented by the treatment with the CXCR4 antagonist AMD3100 or somatostatin.

CONCLUSIONS

CXCR4 and SDF1 are overexpressed in human pituitary adenomas and CXCR4 activation may contribute to pituitary cell proliferation and, possibly, to adenoma development in humans.

The critical role of SDF-1/CXCR4 axis in cancer and cancer stem cells metastasis

Chemokines exert their multifunctional role in several physiologic and pathologic processes through interaction with their specific receptors. Much evidence have revealed that metastatic spread tumor cells may use chemokine-mediated mechanisms. In particular, an involvement of stromal cell-derived factor-1 (SDF-1) in growth of primary tumors and in metastatic process has been demonstrated. Indeed, it has been suggested that CXCR4 expression by tumor cells, plays a critical role in cell metastasis by a chemotactic gradient to organs expressing the ligand SDF-1. Moreover, CXCR4 overexpression correlated with poor prognosis in many types of cancer. In physiologic condition, SDF-1 also plays an essential role modulating stem cell proliferation, survival, and homing through its canonical receptor CXCR4. Recently, several studies have demonstrated the existence of a small subset of cancer cells which share many characteristics with stem cells and named cancer stem cells (CSC). They constitute a reservoir of self-sustaining cells with the ability to maintain the tumor growth. In particular, most of them express CXCR4 receptor and respond to a chemotactic gradient of its specific ligand SDF-1, suggesting that CSC probably represent a subpopulation capable of initiating metastasis. This review focuses on the role of SDF-1/CXCR4 axis in cancer and in the metastatic progression by tumoral cells, as well as the role of CSC in tumor pathogenesis and in metastatic process. A better understanding of migratory mechanism involving cancer cells and CSC provides a powerful tool for developing novel therapies reducing both local and distant recurrences.

Characterization of oligoadenylate synthetase-1 expression in rat mammary gland and prostate: effects of 17beta-estradiol on the regulation of OAS1g in both tissues

OAS1 belongs to a protein family of interferon-induced enzymes characterized by their ability to catalyze the synthesis of 2'-5'-linked oligomers of adenosine from ATP (2-5A). 2-5A bind to the latent Ribonuclease L (RNase L), which subsequently dimerizes into the active form, acquiring the capacity of cleaving cellular and viral mRNA. Several studies indicate that OAS1 is an important inducer of apoptosis in human cancer cells and that it may be regulated by 17beta-estradiol (E(2)). The aim of this study was to characterize OAS1 gene expression in rat mammary gland and prostate, and to analyze its regulation by E(2) in both tissues. It is demonstrated that OAS1g is the most abundant OAS1 gene expressed in both tissues, and that OAS1 protein is present in the nucleus of rat mammary gland and prostate epithelial cells. In addition, it is shown by Real Time PCR that OAS1g is up-regulated by E(2) in rat mammary gland, but down-regulated in prostate, suggesting that the OAS1g gene may be related to estrogen dependent pathways in rat mammary gland and prostate physiology.