The chemokine receptor CXCR4: A homing device for hypoxic cancer cells?

Pharmacologic increase in HIF1α enhances hematopoietic stem and progenitor homing and engraftment

Hematopoietic stem cell (HSC) transplantation is a lifesaving therapy for a number of immunologic disorders. For effective transplant, HSCs must traffic from the peripheral blood to supportive bone marrow niches. We previously showed that HSC trafficking can be enhanced by ex vivo treatment of hematopoietic grafts with 16-16 dimethyl prostaglandin E2 (dmPGE2). While exploring regulatory molecules involved in dmPGE2 enhancement, we found that transiently increasing the transcription factor hypoxia-inducible factor 1-α (HIF1α) is required for dmPGE2-enhanced CXCR4 upregulation and enhanced migration and homing of stem and progenitor cells and that pharmacologic manipulation of HIF1α is also capable of enhancing homing and engraftment. We also now identify the specific hypoxia response element required for CXCR4 upregulation. These data define a precise mechanism through which ex vivo pulse treatment with dmPGE2 enhances the function of hematopoietic stem and progenitor cells; these data also define a role for hypoxia and HIF1α in enhancement of hematopoietic transplantation.

Nef from SIV(mac239) decreases proliferation and migration of adenoid-cystic carcinoma cells and inhibits angiogenesis

The HIV/SIV accessory protein Nef is known to down-modulate cell surface receptors that are required for virus entry such as CD4, CCR5 and CXCR4 to block lethal viral superinfection of the infected cell. The chemokine receptor CXCR4 also plays an important role in promoting cell proliferation, metastasis and tumor angiogenesis. Therefore it was of interest to evaluate if Nef can down-regulate CXCR4 in tumor cells since this could affect these critical prognostic parameters. The CXCR4-expressing cell line ACC3 that was derived from a salivary gland adenoid cystic carcinoma (ACC) of the head and neck was transfected with Nef from SIV(mac239) and cell surface expression of the receptor was monitored by FACS analysis. Real time proliferation of cells was measured with the xCELLigence system (Roche, Mannheim, Germany). Cell migration was detected by an in vitro scratch assay. Similarly, COS-7 cells were co-transfected with CXCR4 and Nef and were treated as described for ACC3. In vitro tube formation was deployed to assess the effect of Nef on angiogenesis. siRNA was used for CXCR4 knockdown. Cell surface down-modulation of endogenous CXCR4 could be observed in ACC3 cells after Nef-transfection as well as in COS-7 cells after co-transfection of CXCR4 and Nef. Proliferation as well as migration of Nef-transfected ACC3 tumor cells appeared significantly reduced. In vitro tube formation was significantly lowered after Nef-transfection or CXCR4 knockdown with siRNA. SIV-Nef could serve as an interesting tool to study the biologic behavior of CXCR4-expressing tumors such as ACC. Deploying SIV-Nef thereby could help in the discovery of new therapeutic approaches for the treatment of ACC and other CXCR4-expressing tumors.

How lithium treatment generates neutrophilia by enhancing phosphorylation of GSK-3, increasing HIF-1 levels and how this path is important during engraftment

Lithium is commonly used in psychiatry for mood stabilization. Lithium treatment results in neutrophilia, increased platelets and increased circulating CD34+ haematopoietic stem cells, HSC. This paper outlines the newly discovered mechanism by which this occurs. Glycogen synthase kinase-3, GSK-3, phosphorylates and thereby inactivates hypoxia-induced factor-1, HIF-1. HIF-1 is a transcription factor triggering transcription of multiple genes related to adaptation to hypoxia, among which is CXCL12. CXCL12 forms the primary homing gradient for CD34+ HSCs towards the hypoxic, trophic bone marrow niche to which they must go to thrive. Lithium inhibits GSK-3 thereby increasing active HIF-1 that results in a stronger CXCL12 homing gradient. Trophic niche function is enhanced, ultimately resulting in increased production of neutrophils, platelets and CD34+ cells. Sitagliptin is a new drug to treat diabetes that coincidentally inhibits destruction of CXCL12. Thus, lithium and sitagliptin enhance CXCL12 by different paths, potentially increasing trophic niche function. Awareness of this path is important in HSC transplantation.

Hypoxia, gene expression, and metastasis

Hypoxia poses many problems to the treatment of cancer. Hypoxic tumors are more resistant to chemotherapy and radiation. In addition, hypoxia induces a number of genes responsible for increased invasion, aggressiveness, and metastasis of tumors. The augmented metastatic potential due to hypoxia-mediated gene expression is discussed in this section. Particular attention is given to recent studies of specific genes involved in the key steps of metastasis, including extracellular matrix interactions, migration, and proliferation.